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Credit: Susan Ting
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Interview of Samuel Ting by David Zierler on 2020 July 24,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/44898
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In this interview, David Zierler, Oral Historian for AIP, interviews Samuel C.C. Ting, Thomas D. Cabot Professor of Physics at MIT and Guest Professor of the Director General of CERN. Ting describes his long-term, unpaid affiliations with CERN and DESY, he recounts his childhood in Michigan, and he describes the opportunities that led to his parents to pursue graduate degrees at the University of Michigan. He explains why he returned with his parents to China before the Second World War, and he describes his family’s experiences during the war. Ting describes his own decision to return to the United States for his undergraduate studies after his family fled from the mainland to Taiwan in 1948, where he lived for eight years, before enrolling in the engineering program at the University of Michigan. He conveys his love for Michigan football, his near brush with the draft, and he explains his decision to remain at Michigan for graduate school. Ting explains his decision to focus on experimentation after initially considering theory, and he discusses his work on the Bevatron at the Lawrence Radiation Laboratory in Berkeley. He describes his dissertation research on pion proton elastic scattering, and his contribution to the finding that that diffraction peak of this scattering does not shrink with increased energy. Ting explains the opportunities that led to his work at CERN to work on proton-proton scattering with Giuseppe Cocconi, and his positive experiences as a junior faculty member at Columbia University. He explains his collaboration with Stanley Brodsky and this connection with his work at DESY, and he relates Feynman’s humorous congratulatory telegram shortly after he won the Nobel Prize on the J particle. Ting explains the significance of this work, and that of Burt Richter at SLAC whose work was entirely independent from Ting’s. He explains his decision to deliver his Nobel acceptance speech in Mandarin, he describes the challenges of distraction owing to the recognition, and he explains how he became interested in space-based experiments. He discusses his increasing involvement with NASA and the Department of Energy (DOE) in pursuing his goal of large-scale experiments, where he has concentrated on measuring the spectrum of electrons. He explains the origins and outlook for the Alpha Magnetic Spectrometer (AMS), and he projects that attaining higher energies will continue to advance fundamental discovery which will serve as complements to land-based accelerator experiments. Ting discusses the discovery of the gluon by the Positron-Electron Tandem Ring Accelerator (PETRA) collaboration, and the influence of his research on the standard electroweak model, and he reflects on what it will take to understand dark matter. At the end of the interview, Ting expresses gratitude for the support he has received from MIT over the course of his career, and he makes the case for why governments should continue to support basic science research, even in fields for which no immediate benefit to humanity is readily apparent.
Okay, this is David Zierler, Oral Historian for the American Institute of Physics. It is July 24th, 2020. I'm so happy to be here with Professor Samuel C.C. Ting. Sam, thank you for being here with me today.
It's a great honor. I'm waiting for you to ask questions.
Okay, so we'll start with an easy one. Please tell me your title, and all of your current institutional affiliations.
My title is Thomas D. Cabot Professor of Physics at MIT and Guest Professor at the European Organization for Nuclear Research (CERN). There are other honorary titles, but I do not remember the exact names.
So, your affiliation with CERN is in what capacity?
I'm a Guest Professor of the Director General, but non-paid.
How long have you been in that position?
I first went to CERN — let me think, March 31st, 1963, before you were born. I've been there for a long time. I've had that position, must be, '77 or '78. Around that time.
And in the same role. You've been working hard at CERN ever since.
Not working for CERN as a CERN employee. CERN really supports us even though United States is not a member nation of CERN. I've been spending my entire career in Germany at DESY and in Switzerland at CERN, with the exception of the International Space Station and one experiment at Brookhaven National Laboratory in the U.S. Both DESY and CERN know me well and treat me as one of them.
It tells me how much you must love the science at CERN to be working in an unpaid capacity for all of these decades.
I am solely supported by MIT as a professor and the U.S. Department of Energy supports my research. CERN provides the use of the accelerators and technical facilities and the title of Guest Professor of the Director General.
Well, Sam, let's take it all the way back to the beginning. Let's start with your origins and your parents. Tell me a little bit about your parents and where they were born in China.
They were born on the opposite side of the Pacific from California, a province called Shandong. I don't remember when they were born, but I think around 1910 or 1911. They met as undergraduates at university.
What university did they go to?
Guanghua University in Shanghai. My mother was very active. She was in theater productions and was a university basketball player. She studied psychology and was a very attractive lady. Later on, she told me many boys were very interested in her, but she wanted to marry somebody intelligent. My mother noticed that my father always seemed to be getting top grades. Later on, they both went to the University of Michigan as graduate students, were married there, and then later I was born at the University of Michigan hospital.
Were your parents the first in their families to go to college, or was there a tradition of higher education even before them?
My mother's father studied civil engineering in Japan. When he returned to China, he worked on the trans-Asiatic railroad. This was the time of the Qing Dynasty. When he looked at China and observed the extremely poor conditions, he decided to sell all his family belongings and organize a revolution. A few hundred people joined him, but the revolution failed. He went into hiding in a Catholic church but was betrayed by the French priest, who had been his friend. He was subsequently caught and beheaded in front of the church. Today, there is a plaque in front of the old church commemorating this event. After that, my mother's mother, my grandma, who was then in her 20s and living in a village, had no more belongings because her husband had sold everything. She decided “I'm not going to stay in this village. I have only one daughter who is 3 years old so, I'm going to leave.” So, she left. She was a devoted Christian and knew a few Presbyterian missionaries from the United States, so she went to work with them and gradually learned how to read and write. Eventually, she became a principal of a grammar school herself. My mother grew up in poor conditions. My father, on the other hand, came from a different part of Shandong province. The Ting family has been there for many centuries, since around 1368, and were quite wealthy. At that time, in large Chinese families, the family history was recorded but only the male names and accomplishments were included. Upon marriage, only the family name of the bride was recorded. Around 1920, my father's father made a tour around China and came back and told his wife, my grandmother, that the Chinese society will soon collapse. "The only way we're going to save ourselves is to make sure all our children have education." My grandfather decided to sell part of his land so that my father, my uncle, and my four aunts all had good educations. Because of this single act, during this period of turmoil, they managed to survive. My father told me when he went to the United States, at that time, there was no Pan Am, no United airlines. He took a steamship, the President Cleveland, and he bought himself a first-class suite. At that time, China was quite poor. No one had ever seen a twenty- year old sitting in first-class before. Unfortunately for him, he had very serious motion sickness, so from Shanghai to Yokohama, and Yokohama to Los Angeles, every day he ate only one apple. He couldn't do anything because of the motion sickness. So, that's how he went to Michigan. My mother arrived shortly afterwards. They were married at the University of Michigan and later on I was born at the university hospital.
Sam, what were the opportunities that allowed your family to come to Ann Arbor?
I do not know. The University of Michigan always had a tradition to accept students from the Far East.
So, your parents came there as students, not as professors.
As graduate students.
Was their intention to be there to take a few courses, or were they supposed to finish their degrees there?
They wanted to finish their degrees. My mother was quite nationalistic because her father was killed during the revolution. There was no question that they'd go back to China. I was only a few months old, so I had nothing to say. That's how I was brought back to China.
Sam, how was your parents' English when they got to America?
I have no way to know. Later on, I noticed my mother had many American friends, even when they were in China during World War II, and later on in Taiwan. My father was more introverted. He didn't have too many friends.
Did you gain American citizenship by virtue of being born here?
Yes, because I was born in Michigan on January 27, 1936. It must have been late in 1936 that my parents went back to China and I went along with them. The war had started with Japan, and so I started at a young age taking a lot of trips, but as a refugee. My earliest memory was being in a sampan sailing on the Yangtze River. On both sides, there were laborers pulling the boat up the river to Chongqing. When I was young, there were a lot of Japanese planes which came over for visits. So I had very little chance to go to school. Most of the university communities where my parents worked stayed in the caves because of the Japanese bombings.
Sam, how badly did your family suffer during the Sino-Japanese War, and the war in general?
During the Sino-Japanese War, I stayed in Chongqing. That was the wartime capital of China. I remember quite a few times I was on the critical list in the hospital. The first time I remember was I was in a hospital for contagious diseases, and a nurse came in and tied a red ribbon around the bed. I noticed my mother’s face changed, and she seemed to have tears in her eyes. After I recovered, I asked her what happened. She said, "A red ribbon means you were on the critical list." Another time, I had pneumonia, my lungs had stopped functioning. The doctor told my parents, "Why don't I give him some sleeping pills so he can pass away peacefully?" My parents said, "No, absolutely not.” So, that was not the best time in my life, mainly because everyone was really fighting for survival. At Chongqing, I did go to school on and off for a very short duration. Occasionally, the school was filled with wounded soldiers in rather bad shape. After World War II, we went to Nanjing, which was once again the capital of the Nationalist government and I tried to go to school, but then the Communists came and I had to leave there in 1948.
Sam, was this your first exposure to formal education?
No, my first exposure to formal education was in Chongqing. I remember I went to a school, and sat on a chair in the third row. The local students spoke a different dialect, and I couldn't understand it. So, I found it very, very boring, so I just left.
Were your parents okay with that?
The school belonged to the university where my mother was a professor and a dean. The teachers apparently knew who my mother was and didn't tell her until the end of the term. She found out I never showed up to school. I just went out to play and tried to avoid school. So, I really started my education formally for a short time in Nanjing, in 1946-48.
Sam, I want to ask if you have any recollection of hearing about the atomic bomb attacks of Hiroshima and Nagasaki.
I remember three things. The first, Pearl Harbor. I remember that one day in Chongqing my parents were quite excited because they realized that China was now no longer alone. Indeed, after Pearl Harbor, the frequency of the visits of the Japanese planes was markedly reduced as they had a bigger enemy to fight. The second thing I remember is the atom bomb. I asked my father what was an atomic bomb and he explained it to me. The third thing was the Japanese surrender in 1945 and the whole city of Chongqing went wild with relief.
Sam, I wonder if even at such a young age, hearing about the atomic blasts impressed upon you the power of physics, or at least science, generally.
I would say the following: what was important for me, even though I didn't go to school, was my father and my mother always told me stories of physicists. Isaac Newton, Michael Faraday, James Clerk Maxwell, and also, I've heard the names of Rutherford, Darwin and Freud. I was familiar with these scientists. My father was a professor of civil engineering and fluid mechanics. He taught simultaneously in two or three universities. Because of the low salary of professors in those days, you were allowed to take two or three jobs at the same time. One of the universities belonged to the military. They had an exhibit of machines. I remember visiting with my father. That was an important visit because I was very curious about what I saw and how they worked. Also, my mother's mother lived with us throughout the years. She was quite nice and always sat with me on summer nights in the backyard and we looked at the stars together. We tried to imagine whether there are lives on different planets. But I didn't have really a formal education. I was definitely not the best student.
Did your father involve you in his scholarly work at all? Did you learn about engineering or mechanics from him?
Most of his friends were mechanical engineers, and civil engineers both in China and later on in Taiwan. This is the reason why, when I first went to Michigan, I went to the College of Engineering to study mechanical engineering, not knowing anything better.
Did you admire your father? Did you want to follow in his footsteps to pursue engineering?
I admired his intelligence and his memory but I always had some disagreement with him. He came from a very wealthy family, and although he was well educated, he was brought up in a traditional way. I always had a different opinion, and he always thought one should respect old traditions because China has a long history and long civilization. I always felt one should move forward. So, we often had rather intense discussions on this, ever since I can remember.
But this is about history and politics. It's not about science.
No, not politics, just tradition, just life. I think one should move forward.
Sam, can you tell me about the circumstance leading to your own decision to pursue education in the United States?
Yes. We went to Taiwan in 1948. So, that really was the first time I had a stable education.
Now, when you say you went to Taiwan, were you escaping mainland China at that point?
Why? Tell me about your family's politics and why they would have had to escape.
Not politics, but my mother, because of her father, belonged to the Nationalist party. Because her father was killed as part of the Nationalist revolution, she naturally was very sympathetic to the Nationalists. That's why we went to Taiwan. My father basically followed her.
So, they had no loyalty to Chiang Kai-shek. That was not part of it.
My parents never talked to their children about politics.
Did you know your parents to be anti-Communists?
In 1948, they may have been. Otherwise, they would not have left. I think another reason they left was because my father came from a rather wealthy family that had a lot of land. I think probably that was a reason. I was not consulted.
Wealthy people with a lot of land generally are not Communists. Sam, what were your impressions of Taiwan when you got there? Did it feel like it was part of China, or did it feel like a different country to you?
When I landed in Taiwan, I noticed in the streets there were a lot of fruits; papayas, guavas, a lot of tropical fruits which I had never seen before. That was my impression.
It must be a new country with all of these delicious, exotic fruits.
But the written language is the same, same customs, same traditions, and same people.
Same people — you mean Han Chinese?
Han Chinese. In Taiwan, there are also some Aborigines but I did not know any. Let's put it this way: I was there from 1948 to 1956. I first went there as a fifth grader, and then sixth grade, and then I went to junior high and then high school. After high school, I spent a term in a provincial engineering college in the southern part of Taiwan. Around that time, my mother reminded me that I was born in Michigan. She was the president of Michigan Alumni Association of Taiwan. So, I went to the U.S. Embassy — at that time there was an embassy — and got my passport and prepared to go to Michigan. I took a flight on Northwest Orient from Taipei to Okinawa, Okinawa to Tokyo, Tokyo to Anchorage, Anchorage to Seattle, Seattle to Minneapolis, and Minneapolis to Detroit. I arrived in Ann Arbor on September 6th, 1956.
What were your ambitions in coming to America? Did you intend to make a life for yourself, or you just thought this was the best place for an education and you'll go back to China at the right time?
I did not think of that at all at that age.
Did you feel like your abilities as a student, even though you didn't have the formal education, your natural aptitude was such that you would be best served in the United States?
Well, when I arrived there, I went to see the Dean of Engineering, G.G. Brown, who my parents knew.
He was very generous to your family.
I think my mother, because she was the head of the Alumni Association in Taiwan, knew him. Soon after I arrived in Ann Arbor I went to see him and talked with him. I mentioned that I was going to study mechanical engineering. He said, "I have four sons. They all have grown up and left. We have a lot of room, and you can stay with us."
Sam, how was your English at that time?
Rather limited. Actually, I'm rather limited in any language. During the wartime, I was traveling to different places in China. Different places, each with different dialects. I never mastered any of them. While I was in Taiwan, I was not able to speak the local language but the written language was the same. Anyway, I went to the University of Michigan School of Engineering. At that time, there were very few students from foreign countries. I think the total population of people of Chinese origin must have been very small in Michigan. Also, there were hardly any European students at the time. At the beginning, because of the time change, I often fell asleep in class. The professor would call my name because I was asleep in the front row, and I'd wake up and everybody would laugh thinking “There's this guy who doesn't know anything, who could hardly talk, who is always asleep.” After a while, my classmates noticed — this strange guy somehow, always gets his paper back first, with the highest mark. At the University of Michigan, every month, there were exams, called the blue books. The instructors passed out the blue books and gave the exams. The student who got the highest grade got his blue book back first. Classmates began to talk to me, and I began to get to know my classmates.
Sam, when I asked you about your early impressions of Taiwan, obviously it was the fruit that sticks out in your memory. What were some of your early impressions of Ann Arbor that stick out in your memory?
My earliest impression was the University of Michigan versus UCLA football game. Since I lived with the Dean of Engineering, he mentioned to me that it was important to go to the games. Also, at that time, every student must purchase a set of season tickets. One Saturday, I went to the first home game. I was immediately impressed because it didn't take me long to figure out what was going on. It is because of that, even today, after so many years, I always try to go back once a year to see a game (but not this year).
Really? It must have been unlike anything you had ever seen before.
It was something I enjoyed and could understand. I also noticed — actually, it takes special skills to be a player, because you have to make a decision very quickly. Otherwise, the consequence could be rather unfortunate. Anyway, I enjoyed the game.
Sam, at what point did you switch your focus away from engineering and more towards mathematics and physics as an undergraduate?
I think it was the end of the first year, my advisor was Professor Robert White (who was a very distinguished engineer. I think he had his picture on the cover of Life Magazine in the '40s), I went to see him, and he took a look at my grades, and said, "You're no mechanical engineer." At that time, there were no computers, mechanical engineers had to make precise drawings with a top view, a side view, and an end view of engineering elements, which I found difficult and I also couldn't draw my lines straight.
You can't be an engineer if you can't draw a straight line.
In the engineering college, there's also an engineering physics degree, and an engineering math degree. Professor White, after looking at my grades, suggested that I pursue engineering physics and engineering math degrees simultaneously, and also said, "I don't think you're going to pass sociology, and all these soft courses. You just concentrate on mathematics and physics. And also, why don't you skip the undergraduate courses. Why don't you start taking courses in the graduate school?" So, the first year I was 20 years old. I was the oldest in my class. The second year, I began to take courses in graduate school, I was no longer the oldest in the class. After three years, I got a degree in engineering physics, and a degree in engineering math.
Sam, I want to ask you, what area in physics, over the course of your undergraduate, did you feel most comfortable in, and that you thought that you would pursue in graduate school?
The courses were interesting, but I did not develop a particular focus on any one of them. I went through all the courses rather quickly.
So, it was just a matter of broad exposure for you.
Yes. However, I never missed a single football game!
Sam, at what point did you realize that you would not be going back to China any time soon, and that you would want to stay in America to pursue a graduate degree in physics?
After I graduated in 1959, the first thing I received was a notice from the draft board. At that time, there was a draft. The years I was in China, Taiwan and the years I was in Michigan, I never heard from this board. But the day I graduated, they sent me a note that I had to go to Okinawa and later on I guessed to Vietnam. First, I had to have a physical exam in Okinawa. I wrote to them, "I live in Michigan. Why do I have to go to Okinawa? I'm no longer in Taiwan." At the same time, because of the launch of Sputnik by the Soviet Union, the U.S. Atomic Energy Commission was sponsoring a nationwide competition for university graduates in hard sciences. I participated in that national competition because if you were selected, you could go to any university, very good universities (Chicago, Harvard, Princeton, MIT, or Michigan, …) for graduate work. The Atomic Energy Commission will pay the tuition, and you will also get $2000 a year as a stipend, which at that time was quite a bit of money. Fortunately, I passed that exam. I think it was quite important for me. I wrote to the Atomic Energy Commission mentioning I went to New York for a physical exam by the U.S. Army and was classified as 1A, ready to be drafted. The Atomic Energy Commission wrote a letter to my draft board, and said, "You should not draft this guy. He's very important to U.S. national interests." And then I heard back from the draft board that I am exempt for life. This is how I managed not to serve in Vietnam. Then I went to visit the University of Chicago, I went to Princeton, I went to Columbia, but finally decided I should stay in Michigan, because I was familiar with the university and I don't have to take any courses. I already took a lot of graduate courses, and I probably could get my degree quickly. That's why I stayed at Michigan.
Did you think about other graduate programs at all, or that was your focus? You wanted to stay put.
I remember a very impressive conversation with Robert Dicke of Princeton on cosmology. When I decided to stay in Michigan, like all the physics students with good grades, I wanted to do theoretical physics. I began my research with Professor George Uhlenbeck. You know who he was, of course.
Uhlenbeck, after I was with him about a month or two, had an afternoon meeting with all of his graduate students. There were three or four of us. He said, "If I were to live my life over again, I would be an experimentalist rather than a theorist." I was very surprised. I discovered that one of the great theorists of the 20th century wanted to be an experimentalist. I asked him why? He said, " Whereas an average experimentalist is very useful because every measurement is useful, an average theorist is not. You can count on your fingers how many theorists made a difference in the 20th century." A few hours after this conversation, I went back to see him and said, "You're right. I should leave you, and I should try to do experiments." That's how I became an experimentalist.
What were his research projects at that time?
Statistical mechanics. I was doing okay, but it is a good thing I left.
And in your decision to become an experimentalist besides the negative decisions for why you felt you couldn't go into theory, what did you learn about yourself in terms of what you were good at that suggested that you would find success with experimentation?
I decided to become an experimentalist and, in the spring of 1960, talked to different professors including Marty Perl and Larry Jones. Do you know them?
Yes. These are famous people.
Yes. They had an experiment on high-energy pion proton elastic scattering at the 6 billion electron volt Bevatron at Berkeley, California. The Bevatron, at the time, was the highest energy accelerator in the world. I had no idea what is the pion and no idea what is elastic scattering or what is the instrumentation involved. But they said, "If you join us, this summer you can work with us at the Lawrence Radiation Laboratory in Berkeley." That was motivation strong enough for me to go with them to Berkeley. So, I went to the Bevatron accelerator floor, and in a very short time, I discovered I knew absolutely nothing. But gradually, I managed to learn. I realized that in order to do experiments, I had to figure things out myself.
When you say, "figure out yourself," does this mean that you were not doing a lot of your learning in courses? This was you working on your own?
Yes, during the summer of 1961 at Berkeley, I learned the techniques. What is a coincidence circuit, how it was designed, what's so special about it, what photomultiplier tubes are and why they only operate at certain voltages, and so forth.
Sam, how did you go about developing your dissertation topic?
That was on pion proton elastic scattering at 3, 4 and 5 GeV. At that time, it was considered an important topic. Our experiment in the summer at Berkeley had a hydrogen target and many optical spark chambers. We photographed the scattering process produced when the 3- 5 billion electron volt pion beam hit the hydrogen target. It's a two-particle elastic scattering, so there were two particles coming out. Once the two final state particles were identified, we knew everything. Initially, we were scanning the photographs manually. I asked myself why don't I develop an automatic scanning machine and let the machine measure and record the elastic scattering process. I designed the scanning machine and had it built and installed very quickly. This enabled us to finish the data analysis very quickly and our results were published in Physical Review Letters on December 1, 1962. The results showed, contrary to the theory at that time, that the pion proton elastic scattering diffraction peak does not shrink with increased energy. This was recognized as an important result. In late December 1962, we were preparing for Christmas vacation. Marty Perl said to me "It's time for you get your degree. Why don't you spend Christmas vacation finishing your dissertation?" On December 23rd I started writing my thesis, and on December 27th or 28th I finished. Perl said, “It was a very important dissertation.” Perl, who had been a student of I. I. Rabi, was extremely supportive of me and I got my degree right away. He then said, "You should go to Columbia University. There are many great physicists there. You can learn from them." He wrote a letter of recommendation to Columbia and that is where I went to start my career.
Sam, I want to ask. At this point, when you defend your dissertation and you're starting to develop an identity as a physicist, professionally, what did you learn about your skills and your interests and what you thought you might have to offer in terms of the biggest questions that were being asked in physics at that time?
I did not think about that in Michigan, I was more interested in getting a degree and watching the football games. I really did not think about that. What was important were my years at Columbia. I was invited there in the spring of 1963 to give a talk on my work.
When did you go to CERN? Did you go to CERN before you got to Columbia, or that was after?
Let me comment on that. I gave a talk at Columbia, and at that time there was no PowerPoint, there were no transparencies. You wrote on the blackboard. So, I described my experiment in front of a distinguished audience of well-known scientists such as I. I. Rabi, Charlie Townes, T.D. Lee, Polykarp Kusch, Jack Steinberger, Leon Lederman, C.S. Wu, Mel Schwartz and others. I remember when I was giving the talk, everybody was listening except for one person in the front row. A very young professor was continuously shaking his head, meaning my talk was rubbish. I realized this must be Professor T.D. Lee because he was very young. Nevertheless, the other professors had different opinions, so they offered me an instructor job. During the discussion with Professor Kusch, who was the head of the department, Kusch said, "Mr. Ting, we just let go of Carlo Rubbia, we will give you a try.” That was the first statement I got from him. I thanked him and said that I just received a Ford Foundation Fellowship to work at CERN for one year and, since I had never been to Europe, I wanted to go to CERN for a year before starting at Columbia. He said "Fine" so that's how I went to CERN.
What did you know about CERN that compelled this interest in you?
Nothing. I'd never been to Europe before.
So, you weren't particularly interested in accelerators, or particle physics, or any particular project that was going on at the time?
When I went to CERN, since I had done the experiment on pion proton scattering, I found that there was a group doing pion-proton, proton-proton scattering led by Giuseppe Cocconi who used to be a professor at Cornell. I worked with him, and began to learn many things from him. I found him to be a very gifted physicist, looking in great detail about every aspect of the experiment. Also, he was a very cautious person. I remember he always mentioned to me, "You have to suspect everything. You need to assume it could go wrong at any moment." I used to take night shifts with him, and he would tell me of his experiences as a physicist and his experiences working with many other distinguished physicists. During the year at CERN, I also worked in another group. In that group I worked with a French physicist named Marcel Vivargent, and two German physicists, Klaus Winter and Gustaf Weber. After that, I went back to Columbia. That experience at CERN was very important to me.
How was your year in CERN important?
Because I really learned what doing an experiment means. What instrumentation means. What accelerators mean.
Also, perhaps, Sam, you learned what collaboration means.
On that note, who were the most important people that you worked with at CERN?
Giuseppe Cocconi, Klaus Winter, Marcel Vivargent, and Gustaf Weber.
So, besides what you learned, Sam, what did you achieve there in terms of your research and pushing physics ahead?
Instrumentation. I really learned the importance of instrumentation and that it has the possibility to malfunction at any moment.
Looking back, did CERN have the most advanced instrumentation at that point in the world?
No. At that time, CERN had just completed the construction of the highest energy Proton Synchrotron (PS). Many physicists were looking at what experiments were done in the U.S. and tried to repeat them. The U.S. already had many years of experience at Berkeley, and at Brookhaven.
What did you learn about instrumentation that was so important? Was it calibration, was it building? What exactly?
Everything. Because of my experience at CERN, until recently, almost all the electronics for triggering and data collection in my experiments were designed and tested by me. This involved knowing when the signals arrive, how long the signal cables should be, under what conditions is there a coincidence between the signals, and when do you collect the data. These features have to be thoroughly tested and understood to ensure the experimental results are correct. There's always something to check and double check.
In what ways did your experience at CERN really advance your abilities as a physicist?
I think I really developed an interest in the importance of instrumentation. Because I know about the limits of instrumentation and always cautious that signals could go wrong. A redundant backup system is essential.
Sam, when you got back to Columbia, how did you go about establishing a research agenda?
I worked with Leon Lederman. Do you know him?
So you did not interview him.
He passed away recently.
I know. It's very sad.
Yes. At that time, T. D. Lee had a model of quarks with integer charge. Not fractional charge, but integer charge, with heavy mass. Leon and I decided to search for Lee’s integer charged massive quarks at the just completed highest energy accelerator, the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory. To reach the optimal sensitivity, we decided that we had to direct the entire AGS proton beam to our target. I moved to Brookhaven and started talking to the accelerator staff about how to do this. Our detector was composed of two nearly identical magnetic spectrometers in tandem. Each spectrometer measured independently the momentum, mass, and charge of the particles produced by the collision. The two spectrometers were separated by a strong magnet. In this way, if a false signal from the first spectrometer comes from a particle collision from an edge of the magnet, it will not be measured by the second spectrometer. Only if you have the coincidence of an identical signal in the first measurement and in the second measurement, you know it is genuine. The result of the experiment ruled out the existence of integer charge quarks, but we did discover anti- deuterons.
Did you work with T. D. Lee directly?
How was your experience at Columbia overall? Was it a warm department to work in?
It was a very good experience. That's where I met Rabi, Steinberger, Schwartz, Lederman, Lee and I also met the famous experimentalist Madame C.S. Wu. These were really great physicists.
Your affiliation there was as a post doc, or as a faculty member?
First as an instructor, and then later on I was promoted to assistant professor.
Who among the senior faculty did you consider to be mentors to you?
No mentors. If anyone, perhaps I. I. Rabi. We were from different generations, but he had a unique way of looking at things.
Can you talk about that? In what way was his perspective unique?
He always had a way of getting to the point in a penetrating way.
Was he approachable? Would you be nervous around him?
No. He was very approachable. At least, with me.
What was his research? What did you see that he was working on during your time together?
During my time, he was already retired. He received his Nobel Prize in 1944 for MRI.
Sam, can you talk about your work at DESY in Germany? How did that come together?
While I was at Columbia, I did a theoretical paper with Professor Stanley Brodsky. Do you know who he is?
Do you know him well?
He is a professor of theoretical physics at Stanford Linear Accelerator Center (SLAC). We did a calculation on trident production from electrons. In this process, the electron scatters from a nuclear target and produces a virtual photon which transforms into an electron-positron pair. So, in the final state we have the original electron, plus an electron-positron pair. Now, you have two electrons in the same state. Then the question is: are they governed by Bose-Einstein statistics or by Fermi-Dirac statistics? By measuring the rate, you will know which statistics determine the final state. We did this paper and I began to realize the elegance of Quantum Electrodynamics (QED) as formulated by Feynman, Schwinger and Tomanaga. At that time, there were two important results announced of a violation of Quantum Electrodynamics, one from an experiment at the Cambridge Electron Accelerator (CEA, jointly managed by Harvard and MIT) and the second from the Cornell electron accelerator. Both experiments studied the photoproduction of an electron-positron pair in the field of a nucleus, the Bethe-Heitler pairs. These experiments tested Quantum Electrodynamics by measuring the size of the electron. Both experiments found, that at a distance of 10 to the minus 14 centimeters, Quantum Electrodynamics is incorrect. The rate is much higher than QED would predict. I looked at these results carefully and I decided to drive from New York to Cambridge to talk to Professor Frank Pipkin of Harvard. He was the leader of the experiment at the Cambridge Electron Accelerator. Unfortunately, there was an enormous electricity breakdown. The whole Cambridge area was dark, so I talked to him, and never saw his face. He and his team were very polite to me, but they also made it clear saying, "You are alone, by yourself, with no budget. You've never done an electron experiment. You're welcome to join us." Then, I went back to Columbia and got in touch with my friends with whom I had worked at CERN; Klaus Winter and Gustav Weber. They said, "Well, we are just building an accelerator in Hamburg. “We're looking for people. Why don't you come to Hamburg to do this QED experiment? We will help you to obtain the support”. So, I went to talk to Columbia, and they said, "We'll give you a year’s leave and support your salary for one year." That was very kind of them.
You saw this as a very special opportunity.
Yes. So, I went to the Deutsches Elektronen Synchrotron (DESY) laboratory in Hamburg, Germany. I talked to the founding director, Willibald Jentschke, about my idea of redoing this important experiment. He quickly decided to support me and provide the funding, instrumentation and technical support. In a short time a few graduate students, Martin Rohde, Ulrich Becker, A.J.S. Smith joined me for the experiment and later Gary Sanders joined us. We benefitted enormously from working together with talented technicians, Ingrid Schulz and Peter Berges.
We worked on a different design of an experiment from those used at CEA and Cornell. The main point was if you want to do an accurate experiment, you must know the detector acceptance and therefore the volume from which particles are measured after production. You cannot use the edge of a magnet to define your acceptance, because additional particles can be produced by scattering from the edge of the magnet. All the detectors must be designed and built to be smaller than the aperture of the magnet in order to accurately define your acceptance. Of equal importance, because of the large pion pair background compared to electron positron signals, you must clearly separate electron positrons from pion pairs with multiple redundancy. This was accomplished by having two independent but identical magnetic spectrometers, one for positrons and one for electrons, each measuring the signal twice. The first time you measure the momentum, and this must agree with the second measurement of the energy. For a genuine electron positron signal, energy and momentum must match at high energies. This agreement ensures that your signals are genuine and not a misidentification of pions as electrons. Is that clear to you?
The pair spectrometer design used in this experiment was gradually refined to do the leptonic decays of vector meson experiments which required a separation power of electrons and positron pairs from pion pairs of 1 in 100 million. Ultimately, the design principle and the operational experience of the pair spectrometer was used in the construction of the J particle experiment at Brookhaven National Laboratory a few years later which required a separation power between electron positron pairs and pion pairs of 1 in 10 billion.
In less than a year of running my first experiment at DESY, we produced results which were in complete agreement with the prediction of Quantum Electrodynamics.
Which tells you what, when this is in agreement?
It means the theory of Feynman is correct. I remember in 1966, there was a high energy physics conference at Berkeley. At that time, it was called the Rochester Conference. I went with the DESY group to this conference. I was not on the schedule to speak. Nobody knew who I was. Nobody knew my experiment existed. Willibald Jentschke and I went to talk to the session chairman, W. K. H. Panofsky. You know Panofsky?
Panofsky said, "The schedule is full. We have a detailed presentation on the QED experiment from Harvard, followed by another presentation from Cornell which confirmed the Harvard result. But we can give you ten minutes at the end." After these two presentations, I was given ten minutes. I showed the design of my experiment and examples of how the trajectory was defined, how the momentum was measured, and how the energy was matched to the momentum. I also presented many experimental checks of our results. Finally, I showed that our results were in complete agreement with Quantum Electrodynamics. This was a very important presentation for the DESY laboratory, because that's the first time people realized the laboratory was doing good work. After the session, I met with Pief Panofsky, Dick Feynman, and I. I. Rabi, all of whom were quite pleased with my results. Those were the physicists with whom I have always kept in constant contact, particularly before I start a new experiment.
What would you learn from them? What kind of advice would you get from them?
I'd just tell them about my experiment, and they would listen carefully.
Of course, they were very interested in what you were doing. Why do you think that's so? What was so significant about your research that it would gain their attention?
This I do not know. I have great respect for these physicists.
But of course, it's more that they just like you. They understand that what you're doing is important.
I remember the last time I saw Dick Feynman in Pasadena; he was already quite sick. He came out of the hospital to talk to me. That was about my experiment, L3, at CERN with the large electron positron collider, LEP. I explained it to him, and I asked him, "What do you think of this experiment?" He said, "Well, Sam, what else are you going to do if you don't do this?"
That's a very Feynman thing to say, right? Sam, I've heard it said of Feynman that even at the end of his life, he still maintained his boyish wonder of the world.
Yes. Such people are really rare.
So, you continued on with the research. He gave you good advice.
Yes. The third day after I received the Nobel Prize, I got a telegram from him. The telegram said, "Congratulations Sam, but why do they give prizes to guys who discover things that I didn’t expect and don’t understand? Please don’t let the prize go to your head. I challenge you to discover something that I can easily understand.”
Meaning that it shouldn't be used as a platform for you to talk about things —
That's what he said.
What was the day like when you received that news?
It was nearly noontime and I was at CERN doing an experiment in the Intersecting Storage Rings (ISR). There was a phone call from Sweden from the Secretary General of the Nobel Committee informing me that I had received the Nobel Prize in Physics along with Burt Richter of the Stanford Linear Accelerator Laboratory (SLAC). The MIT community was very happy and had a big party that day in Cambridge. There was a big celebration, but the only person who was not present was me because I was at CERN.
Sam, was this news a total surprise to you? I've talked to some Nobel Prize winners who thought the news might be coming. Everybody is humble, and they can't be certain, of course, but sometimes there's so much buzz around the research that it seems like a good possibility. Did you sense that there was buzz around your research that might lead to this recognition, or was this really a shot out of the blue?
When I was at Columbia University, I noticed there were many great physicists who have done very important work which deserved a Nobel Prize. Every year around October, they appeared to be very nervous, and very tense. After the J particle announcement, I decided I have done my work, and if the Nobel Committee thinks it's worth it, they will tell me. I was not thinking about it. Also, the Nobel Committee made their decision rather quickly. Normally, they let you wait for many years.
Sam, you're such a humble person, and you downplay the significance of your work. I wonder if you ever felt badly that you received this recognition when you're aware of so many people who did equally impressive work in your mind, and who never received this level of recognition.
I would say the Nobel Committee has been very careful. If you look at the physics awards, the ones who received the award really have done important work. But as you just pointed out, there is also a large group of people who really have done very good work, and deserve it. I hope they will get it.
But who never did.
Well, they're still alive.
Sam, in what ways did receiving the Nobel Prize make your life more difficult?
The first congratulation telegram was from Rabi. Rabi said, "Well, Sam, from now on, you will find that funding will be easier." Indeed, this is the case. It has not made my life more difficult, mainly because I always just work on my experiments. I don't get involved with things I'm not familiar with.
So, you were able to continue on with your research and not become too distracted.
No, I'm not distracted at all. I think one reason, probably, is because when I received the Nobel Prize, I was 40 years old. Not ready to retire.
You had a whole life ahead of you.
Sam, I know this is going to be hard for you to explain, but I have to ask. The Nobel Prize Committee didn't just make up why they decided to give you this award. So, can you explain the significance of your research and why it would be recognized at this level?
Before my experiment, with the exception of electrons, positrons, protons, and anti- protons, all the other elementary particles have a very short life. Very, very short life. After the discovery of this particle, which I called J and Richter called Psi, a family of new particles was discovered. The members of this family have a lifetime ten thousand times longer than the rest of the elementary particles. This is equivalent to if someone went to a village somewhere in South America and found in that village that everyone has an average age, not around 100 years old, but a million years old. This means the people in this village are definitely different from the rest of the population. It means something new and unexpected has happened. No one predicted this. In the citation by the Nobel Committee the award was given “for the discovery of an elementary particle of a new kind”. A particle with extraordinarily long lifetime doesn't follow expectations. Now, physicists believe the J particle is from the bound state of a charm quark and an anti-charm quark. Before this discovery, physicists thought there were only three types of quarks. This is because three types of quarks can explain most of the existing physics phenomena at that time. With this discovery we're at four, and later on a fifth type was found followed by a 6th type. Currently, physicists think there are only six types of quarks. Of course, if you don't do experiments, you will never find how many types of quarks really exist and, more importantly, if the quark model is really correct. When I proposed this J particle experiment, it was rejected by CERN and rejected by Fermilab. Most theorists believed it was a useless experiment, and most experimentalists believed it was too difficult to carry out. In the proposal (BNL-598) of this experiment to Brookhaven National Laboratory, I didn't use the search for new quarks as the motivation. I used the fact that, when I was at DESY, my group did a series of experiments on the relationship between photons and massive photons (vector mesons). Vector mesons are particles (Rho, Omega, and Phi), which have the same quantum number as photons but each with a mass of about 1 billion electron volts. At high energies, a photon would be expected to transform into a Rho, into an Omega, or into a Phi which then can transform back into a photon and then to an electron-positron pair. Consequently, whereas Rho’s – which are a two-pion resonance, and Omega’s – which are a three-pion resonance, and Phi’s – which are two-kaon resonance will not interfere with each other in their normal decay process. But, they could interfere with each other in the electron-positron final state with a probability of one in a million. This phenomenon was expected but very difficult to observe. I spent quite a few years at DESY studying the relationship between photons and vector mesons (Rho, Omega, and Phi). They, indeed, do transform into each other and do interfere with each other with a probability of one in a million. Therefore, to reduce the background to 1%, the original QED pair spectrometer was designed to have a separation power between electron-positron pairs and pion pairs of one in a hundred million. After completing this series of experiments, I thought, “Why are there only three vector mesons?” and “Why do they all have a mass of one billion electron volts?”, “Shouldn’t there be heavier vector mesons?” That was the reason to do the experiment that I gave in the proposal to BNL. As stated in our proposal to BNL, the reason we didn't propose to perform the experiment at an electron-positron collider was that at an electron-positron collider, you need to know exactly what the mass of the particle is, because the energy of the electron- positron collider must be well defined. To search for particles you need to vary the electron- positron collider energy continuously in very fine steps. But with a large acceptance electron positron pair spectrometer, like I used at DESY, you can cover a large range of masses of new particles so you do not need to know the mass beforehand. Going to the Brookhaven proton accelerator (AGS), enabled us to cover higher masses than at DESY.
Sam, how closely did you work with Burt Richter, and how long was that collaboration?
No, we worked totally independently.
Totally independent. You didn't even correspond.
I had no idea what he was doing.
You didn't know what he was doing, and as far as you can tell, he didn't know what you were doing.
Yes. He graduated from MIT long before I went there.
When did you find out about his work? Was it only as a result of the Nobel announcement?
No. On November 11th, 1974.
So, would you say that you were part of the so-called November revolution but from the outside?
Yes. Panofsky had a program committee meeting at SLAC and invited me to be a member. Panofsky is a person I cannot say no to. I had never accepted to serve on any committee before. So, on November 11th, I went to SLAC to attend the committee meeting, and then I learned that Richter’s group had the exact same result that we had. You can find the history of the discovery in a recollection written by Martin Deutsch, then the Director of the Laboratory for Nuclear Science at MIT, published in Science magazine on September 3, 1975.
What was your decision about delivering your acceptance speech in Mandarin?
When I was young, I often had disagreements with my father. My father followed Chinese philosophy and believed that those who respected ancient tradition are more important than those who develop new ideas. I had a totally different opinion from him. I also noticed that in Chinese culture; people who use their mind come before people who use their hands. Therefore, at that time, there were not so many people of Chinese origin doing experiments. That's why I decided to give the speech in Chinese stating that natural science is an experimental science. A theory, however elegant, if there is no experimental verification, is not meaningful. Only when experiments disagree with theory, do you realize the need for new theories.
Do you think that it had an inspirational effect on young Chinese students who were interested in pursuing science?
This, I do not know. I only remember the U.S. Ambassador to Sweden came to see me, and said, "You are American. U.S. and China relations are very tense." That was 1976. "Why would you use the Chinese language?" I said, "Using Chinese language does not mean I support any political ideas. The Chinese language is one of the oldest written languages”. That was acceptable to him.
You didn't feel any pressure from the ambassador?
No. It was totally harmless. I should mention that I invited some of my key collaborators to the Nobel ceremony and banquet including Marcel Vivargent. He and I had designed and built our four ultra-precise hydrogen gas Cerenkov counters at CERN for the Brookhaven J particle pair spectrometer experiment. These counters enabled us to cleanly separate electron positron pairs from pion pairs to the level of 1 in 10 billion. The four counters each measured one meter in diameter and four meters in length. They were each equipped with a light collecting system consisting of one meter diameter three-millimeter-thick specially designed mirrors, two spherical and two elliptical. Each of these mirrors focused and deflected the Cerenkov light generated by electrons and positrons in the radiator to a parabolic mirror. These counters were the most important instruments in the experiment for discovering the J particle.
To prevent a pion knocking out an atomic electron in the Cerenkov radiator or in the material in the entrance and exit windows, which would result in a pion and an electron travelling forward together resulting in the misidentification of a pion as an electron, we used hydrogen gas as the radiator and 125 microns of plastic foil for the material in the windows. These counters were very difficult to build and had to be completely leak proof as hydrogen gas is explosive. In addition, in the double arm identical spectrometer, each of the Cerenkov counters were separated by a strong magnet so the knock-on electrons which have low energy are swept away and cannot enter into the second Cerenkov counter. Vivargent also sent one of the best young physicists from France, Jean-Jacques Aubert, to Brookhaven to set up and calibrate the four Cerenkov counters.
I also invited my MIT colleagues, Ulrich Becker, Joseph Burger and Min Chen, each of whom made important contributions to the experiment. In particular Becker contributed greatly to the design and construction of the proportional chambers to measure particle coordinates to a millimeter accuracy in high radiation background. Min Chen contributed to the data analysis and Joseph Burger oversaw the entire assembly of the detector.
At what point, Sam, did you feel like you were able to return to your normal life after all of the excitement had died down?
Quite some time. It did really help me a lot. Like the experiment I'm currently doing on the International Space Station (ISS), the Alpha Magnetic Spectrometer (AMS) experiment. It was proposed, reviewed and accepted, and scheduled for launch on a Space Shuttle to the ISS. Suddenly, after the Columbia accident in 2003, the Space Shuttle fleet was retired and science on the ISS was canceled by the White House. Thus, there was no way to get AMS to the ISS. One day in the fall of 2005, I received an invitation from the U.S. Senate Committee on Commerce, Science, and Transportation to testify in a hearing on the future of science in the U.S. They invited four Nobel laureates to give their views. I normally never accept these things, so I was just about to write a letter to thank them but decline because of previous engagements. But my wife Susan said, "This would be a good time for you to remind the Senators how important it is to utilize the Space Station for fundamental science." My ten-minute testimony with a few PowerPoint slides turned out to be very useful as many Senators (Kay Bailey Hutchison, Bill Nelson, among others) attended this meeting and realized the importance of AMS on the ISS. Subsequently in 2008, legislation was unanimously passed (HR6063) to add an additional shuttle flight to the manifest to deliver AMS to the Space Station. In this way, it was very useful to have the Nobel Prize.
Had you considered this area of research before, or this was your entree into this new field?
Space, in terms of starting to think about space.
After the Superconducting Super Collider (SSC) was canceled, I was walking in my garden near Geneva where I have a house near CERN. I was thinking, years ago I did the work on the discovery of anti-deuterons. If the universe had come from the Big Bang, there should be equal amounts of matter and antimatter at the beginning. Now the universe is 14 billion years old, where is the other half of the universe made out of antimatter? I also realized; I'd never done anything in space before and I have no experience on performing an experiment in space. I decided, this is what I should do: to look for antimatter, to study the origin of cosmic rays with a precision magnetic spectrometer in space. This is the origin of AMS.
What were some of the big questions in this new endeavor that you wanted to focus on?
This has been one of the most complex and technically challenging experiments I have ever done. No one has ever put a magnetic spectrometer in space. This is because a magnet in space behaves like a magnetic compass. One side will point North and the opposite side will point South. Thus, with the AMS magnetic spectrometer onboard, the Space Shuttle and the Space Station will experience a large torque and lose control. The key is to design a magnet so that it does not rotate in space. The magnet also must be lightweight so it can be carried by the Space Shuttle. In addition, it must have no magnetic field leakage, so astronauts can be close to the detector without affecting their life support systems. This was accomplished by designing a magnet with two counter-rotating fields, so that the outside fields cancel each other and the inside field add together. In this way, there would be no torque and no field leakage. It took 40 years to figure this little thing out.
Why so long? What's so difficult about it?
I have no idea. When I first proposed this, I went to see Academician Sagdeev. Do you know Roald Sagdeev?
I talked to him, yes. I know him well.
How is he?
Thank goodness, he's doing great.
I talked to him. I invited him to come to MIT, and asked, "Could we do such an experiment on the Russian MIR Space Station?”
Why did you go to Roald? Was he the premier researcher in this field?
He is the former director of the Space Research Institute of the USSR Academy of Sciences. He was the one I knew who has a deep knowledge about performing physical science experiments in space. So, I talked to him and asked if I could try to do an experiment on the MIR Space Station. He said, "You will not survive the Russian bureaucracy. Why don't I introduce you to Dan Goldin, the Administrator of NASA." I think it was May 9th, 1994, I went to see Goldin with Sagdeev and a few of my international collaborators. Goldin listened to my presentation, and afterwards said, "Well, this an ideal experiment for the Space Station, but NASA has already many excellent science programs in space. We have no funds to support a new field. Who will support you?" I said, "The Department of Energy has always supported me.” Goldin said, "There's an agreement between NASA and DOE, just like NASA has agreements with NSF and other government agencies. If DOE makes a request to NASA to install AMS on the Space Station, NASA will honor it. Why don't you have DOE review this experiment and get support from DOE?" I went to DOE and talked to Dr. John O’Fallon who was in charge of the DOE sponsored high-energy physics programs. His first answer was, "We have supported you for a lot of experiments at accelerators, but you have no experience in space. Are you sure you know what you're doing? And the DOE Office of High Energy Physics has never supported a large-scale experiment in space." I replied, "This is very simple. Why don't you organize a Blue Ribbon Panel to review this experiment and provide you with a recommendation? Please choose the best committee you can find from members of the National Academy of Sciences and distinguished engineers" DOE organized such a committee to review AMS and the conclusion was that this is an important experiment to support. Therefore, DOE approved it. Over the years the Blue Ribbon Panel committee has reviewed AMS regularly. The committee members have included Jim Cronin, George Smoot, Barry Barish, and Saul Perlmutter and many other outstanding physicists. When DOE first approved the experiment it was under the condition that they do not increase our budget and we would have to find most of our support from our international partners in Europe and Asia. I want to point out that the composition of the Blue Ribbon Panel committee and their strong support has helped us enormously in obtaining support world-wide.
It's easy to approve with no money.
Yes. DOE initially stated, "We will support you with your existing budget." However, over the last twenty-five years, John O’Fallon, and later Robin Staffin, Dennis Kovar, and presently Jim Siegrist, Directors of the U.S. DOE High Energy Physics programs, have provided extra financial support to ensure the MIT group fulfilled its international obligations. My international collaborators: the Italians (Roberto Battiston, Bruna Bertucci, Giovanni Ambrosi, Andrea Contin, Giuliano Laurenti, Marco Incagli, Franco Cervelli, Bruno Borgia, Piergiorgio Rancoita); the French (Jean-Pierre Vialle, Sylvie Rosier, Guy Coignet, Laurent Derome); the Germans (Klaus Luebelsmeyer, Stefan Schael, Thorsten Siedenburg); the Swiss (Maurice Bourquin, Martin Pohl, Hans Hofer); the Russians (Yuri Galaktionov,) the Chinese (Hesheng Chen, Lin Cheng, Yifang Wang); the Taiwanese (Shih-chang Lee, Yuan-hann Chang); the Spanish (Manuel Aguilar, Javier Berdugo, Carlos Mana); the Portuguese (Fernando Barao); the Mexicans (Arturo Menchaca), and the MIT group (Ulrich Becker, Mike Capell, Peter Fisher, Joseph Burger, Vitaly Choutko, Andrei Kounine, Xudong Cai, Vladimir Koutsenko) all worked together on this experiment. Indeed, all the detectors of AMS were constructed in Europe and Asia, assembled at CERN and tested at the European Space Agency Test Facility. The MIT group’s contribution was mostly in electronics and data analysis.
When we first started, it really reminded me of the first day I was a graduate student at Berkeley. I knew absolutely nothing. I remember Dan Goldin asked me how much the detector weighed, and I did not provide an answer. It did not occur to me, but in transport to space, weight is everything. To support us, Goldin organized a project management team at Johnson Space Center (JSC) composed of excellent space engineers who guided us on how to do things in space. That is how we managed to do this experiment. Just to give you an example: since nobody has ever put a magnet on the space station, we actually built ten magnets. One of them, we tried to destroy to see under what conditions the magnet will fall apart. We found that we could not destroy it. That's really important, because when the space shuttle leaves the ground, it has tremendous accelerations and vibrations, and you don't want your magnet to fall apart and destroy the shuttle. Over the last twenty-five years, the NASA leadership, particularly Dan Goldin and William Gerstenmaier and the managers of the AMS Project Office at JSC (starting with Bill Hungerford, then Jim Bates, Steve Porter, Trent Martin, and now Ken Bollweg), have been most important to the success of the experiment. After a successful ten day engineering flight in June 1998, AMS was launched to the Space Station on space shuttle Endeavour in May 2011. Up to now, we have published eighteen new results in Physical Review Letters. Most of the publications have been selected by the American Physical Society as “Editors’ Suggestions” to signify their importance to the field. The most important thing to emphasize is that none of the results agree with current theoretical predictions. This is, perhaps, because AMS has a large acceptance, high resolution, and a long exposure time. Before AMS, most of the space experiments were carried out on balloons and satellites with non-magnetic calorimeters. Balloon experiments are limited by the short exposure time. Non-magnetic calorimeter experiments on satellites cannot measure the momentum and the sign of the charge of cosmic rays. AMS is a very precise detector in space which can carefully examine all the properties of cosmic rays directly. It is like you're looking at an object with your eye, or with a microscope. You see different things. That's how we gradually changed our understanding of the origin of cosmic rays. We have systematically published results on the electron spectrum, the positron spectrum, protons, antiprotons, and many of the elements on the periodic table.
What have been the major answers that you've gotten so far on the research questions that were originally posed that caused this massive experiment to start?
So far none of our results are what we expected when we first started the experiment. For electrons, we have measured its spectrum from very low energy to a few trillion electron volts based on 30 million electrons. For unknown reasons, this spectrum can be precisely described by just four parameters. Nobody thought this was possible or why it is so. For positrons, the spectrum cannot be explained by these four parameters. The spectrum is totally different than electrons. Unexpectedly, when the positron energy reaches about three hundred billion electron volts, the spectrum suddenly cuts off and decreases quickly with energy. This could be due to the positrons produced by dark matter collisions. We need to continue to collect data to be sure. For antiprotons we found that the spectrum is very much like the positron spectrum. The antiproton spectrum cannot originate from astrophysical objects like pulsars. A sharp cut off, which comes from energy-momentum conservation starting from a dark matter collision with finite mass is the best explanation of the positron and antiproton spectra. For cosmic rays, we have measured the spectra of many different types, from helium up to iron, as a function of rigidity (rigidity means momentum per unit charge). Before AMS, there were very limited rigidity measurements of cosmic rays with 30 to 50% or larger errors. Now, we can study cosmic rays with an accuracy of 1%. For each cosmic ray element we have collected tens of millions of data with energies up to multi-trillion electron volts. Cosmic rays were believed to have two classes. The first class are primary cosmic rays (helium, carbon, oxygen, …) which are produced from nuclear fusion in stars and accelerated by supernova explosions. Then there are secondary cosmic rays (lithium, beryllium, boron, …) which are produced from the collision of primary cosmic rays with the interstellar media. Unexpectedly, AMS discovered that at high rigidities, primary cosmic rays actually have two classes, each class contains elements with unique but identical rigidity dependence. AMS also found that the secondary cosmic rays have their own rigidity dependence which is very different from the two classes of primary cosmic rays. These phenomena were not predicted. It's really, very strange.
When you say it's strange, what would you expect otherwise?
It's not in any theory. When you go through the periodic table, where all the elements are listed, the question is why do the elements behave as they do. Nobody knows this. Nobody has reached such an accuracy at such a high energy.
There are no other magnetic spectrometers in space in the foreseeable future. In AMS, the collaboration is always divided into two or three teams to analyze each subject independently and simultaneously. It is only when the teams agree with each other within the systematic error of 1% that we publish the results in Physical Review Letters. This is because, when you have an error of 1%, there is always a judgment call on what is signal and what is background. Since we have no competition, we try to do this as carefully as we can.
Sam, what does this experiment tell you about what we now know that we didn't know before, and how that might inform the next generation of experiments?
Well, there are a number of things we know that we didn't know before. The functional behavior and the properties of all the cosmic rays that we measured, we did not know before. We knew of their existence, but we did not know their behaviors or their properties.
So, my question is, based on this, what might next generation experiments look like to move the field even further ahead?
We'll go to higher energy. We now go to a trillion electron volts. If you can go to 100 trillion electron volts, you may find different physics. Remember, if you don't search, you never know.
Now, going to these energies, are you convinced that they are scientifically feasible?
Yes. They require the development of superconducting magnets. Large superconducting magnets exist now and are used on the ground but not in space. There is probably a way to do that. We actually built a large superconducting magnet for AMS, but then NASA announced the retirement of the space shuttle fleet so we would not have been able to refill the superfluid liquid helium every three years required for a superconducting magnet. That's why, finally, we chose a permanent magnet.
Do you see AMS as effectively supplanting, or replacing the very real possibility that high-energy accelerator physics that are land based are not going to be a part of our future? In other words, the SSC got canceled, the future of the ILC is very much up in the air. What do you see the AMS contributing as a fully advanced substitute for land base accelerator projects and collider projects?
I think they are complimentary instruments. The future of accelerators on the ground going to higher energies is fundamentally important as you are probing smaller and smaller distances. Despite the theory, you never know what you're going to observe. In space, you don’t know either, but you are probing larger and larger distances at energies that cannot be produced by accelerators.
Had the SSC been built, or if we had the ILC, in what way would that have advanced what the AMS has been able to achieve so far?
So far, what the SSC would have discovered, and what AMS is observing are not directly related. The only thing, is if SSC had been built, the Higgs particle would have been discovered in the U.S. and high energy physics probably would be centered in the U.S.
What has it been like to work on such a massive project with over 500 scientists?
You really need to realize your ability is limited. You need to listen to everyone. Particularly, the young graduate students and young post docs. But also, you need to realize sometimes what we know on the ground, the experience we have on the ground, does not apply in space. The simple fact is that you cannot go there to check and to replace anything and this keeps you worried all the time. But the most important thing for me is to realize my ability is limited and I need to be careful all the time.
I want to ask you, Sam, some more specific questions about various discoveries that you were involved in. What has been the long-range value of the discovery of the gluon, and what work remains to be done in this field?
The gluon was an excellent discovery by our group at PETRA. The gluon is the key particle in Quantum Chromodynamics (QCD). The gluon’s existence had been long predicted and seen indirectly in many experiments. While it's an important discovery, if it had not been predicted the discovery of the gluon would have been even more important. In this way it was different from the discovery of the J particle. No one had ever expected the J. The history of the gluon discovery was recorded in a paper by the Director General of DESY, Herwig Schopper, DESY publication 79/79, December 1979) and in an article in the New York Times, September 2, 1979, and in Physics Today, February 1980.
Were you ever in touch with Weinberg, Glashow, and Salam in your work on muon charge asymmetry?
Yes, I know both Steve and Shelly quite well. When I first came to MIT, I would often meet with Shelly and Steve. We would always go to have lunch together. One of the experiments I did at the electron-positron collider PETRA at DESY was to measure the muon pair asymmetry. The muon pairs from the electron-positron collision should have been symmetric, but we found that they are not, and this is because of the existence of the intermediate vector boson from the Glashow-Weinburg-Salam theory. This was before the discovery of the intermediate vector boson (Z). Both Steve and Shelly were quite excited about our result. (See, Physics Today, August 1982). I seldom talked to Abdus.
In what ways has your work, experimentally validating the standard electroweak model, in what ways has that stood the test of time, and in what ways has that model changed?
I spent 20 years, 1983-2003, doing the L3 experiment at the electron-positron collider LEP at CERN. We published 300 papers in Physics Letters. All the results agreed with the standard model. That is rather unfortunate, because when an experiment agrees with the model, what you learn is limited. When an experiment disagrees with a model, you learn much more, obviously. After 20 years, we've found the electron has still has no measurable size, it is less than 10 to the minus 17 centimeters.
L3 was an experiment involving the collaboration of 20 countries. It was the first large-scale scientific collaboration between the United States, China, the Soviet Union, India, East and West Germany. In total there were 600 physicists working together for 20 years (1983-2003). The experiment had a 300-ton uranium hadron calorimeter with 300,000 detection channels of proportional chambers as well as a six story high, 10 thousand ton electro-magnet. Most of these were constructed and tested in the Soviet Union. It was one of the largest international collaborations in the Soviet Union led by Yuri Galaktionov. In addition to the Soviet Union, the hadron calorimeter was built with Aachen University in Germany, led by Klaus Luebelsmeyer, by ETH/Zurich, led by Hans Hofer and the University of Michigan, led by Larry Jones and Byron Roe. The silicon vertex detector was made in Italy, under the leadership of Roberto Battiston of Perugia University with important contributions from Giovanni Ambrosi and Bruna Bertucci, and by the University of Geneva in Switzerland, under the leadership of Maurice Bourquin and Pierre Extermann. The scintillation counter system was developed at Bologna University under the leadership of Antonino Zichichi with important contributions by Andrea Contin. The muon chamber system was made at MIT by Ulrich Becker, Marion White, and Joseph Burger. The trigger system was designed and built by Masaki Fukushima, Wu Xiaoshiang, Mike Capell, and myself of MIT. One of the most important technical achievements was the development of 12,000 BGO crystals each weighing 1 kilo for a total of 12 tons. When we started the experiment the world’s production of BGO crystals was 4 kilograms per year. The Shanghai Institute of Ceramics under the leadership of the late Dongshen Yan and Zhiwen Yin were able to develop a new technology to produce the 12,000 crystals for L3 in three years time. BGO crystals are now widely used in industry, medicine and science. Marcel Vivargent of LAPP, Annecy, France made major contributions to the supporting structure of the 12,000 crystals and Pierre Piroue of Princeton developed the electronics system along with Bruno Borgia of Rome. Many physicists contributed to the success of the experiment. I recall Harvey Newman, J.J. Blaising, Manuel Aguilar, Shih-chang Lee, Fernando Feroni, Gregor Herten, Jim Branson, Bob Clare, Divic Rapin, David Stickland, Yuan-hann Chang, Keith Riles, Vitaly Choutko, Andrei Kounine, Bolek Wyslouch, Andre Rubbia, Peter Fisher, Susan Ting, Christoph Pauss, Alexei Vorobiev, Joachim Mnich, Thomas Hebbeker, Xudong Cai, Chris Tully, Patricia McBride, Javier Berdugo, Carlos Mana, Wolfgang Wallraff, Sylvie Rosier, Guy Coignet, Laurence Barrin, Manfred Steuer, Thorsten Siedenburg, Tiesheng Dai, Maurice Bourquin, Guoming Chen, Simonetta Gentile, Jasper Kirkby, Yifang Wang, Tofi Azemoon, Hesheng Chen, Yanis Karyotakis, Pier Giorgio Rancoita, Dong Chui Son, and Wolfgang Lohmann. Most are now successful physicist on their own. I am sure there were many others whose names I cannot recall but who also contributed greatly.
Many people in cosmology and astrophysics today believe that it's more likely that major advances will be made in the discovery of dark matter than in the discovery of dark energy. Do you agree with that, and in what ways does AMS push the field forward on dark matter?
So far, our measurements from AMS of antiproton spectrum and positron spectrum can both be easily explained by the existence of dark matter particles with a mass of about 1 trillion electron volts. But we need more data to make sure this is the only explanation.
When will you know, or what will it look like to understand what dark matter is?
If dark matter is a particle, let's say it's a particle with a mass of 1 trillion electron volts, then when two dark matter particles collide, they are going to produce positrons and antiprotons among many other particles. Of all the particles produced by the dark matter collisions, positrons and antiprotons are the easiest to identify because their yield from ordinary cosmic ray collisions is very small. In addition, with the finite mass of dark matter, the spectrum of the positron (or antiproton) must display an energy cutoff. For example, two dark matter particles, each with a mass of 1 trillion electron volts moving slowly and colliding cannot produce a positron or an antiproton with an energy of 3 trillion electron volts. This is just the conservation of energy and momentum. AMS has now observed the positron spectrum cutoff. But still, we need more events to make sure we are definitely observing positrons from dark matter collisions.
More events meaning what? How many more, and how long might that take?
I don't know, at least until 2028 or later.
Well, that's not so long away.
You do not know how long the Space Station will last.
So, maybe you're a little nervous all the time.
Currently during the Pandemic, I use Zoom for four to five hour meetings every day with my colleagues at CERN to review every aspect of the experiment. You cannot take things for granted. The fact that things did not go wrong for ten years does not mean it will not go wrong in the next day.
So, every day you sort of prepare that something can go wrong.
Yes. Fortunately, we have 200-400% redundancy for the key electronics, because in space, there is intense radiation. Radiation can destroy the electronics components. We selected the components by putting them in accelerators in order to choose the most radiation resistant ones. Even with this massive effort, mostly conducted by Mike Capell, Vladimir Koutsenko, Andrei Kounine, Xudong Cai and Yuan-hann Chang, once in a while an electronics component in AMS will suddenly go dead. Then, it will automatically switch to the next redundant element.
Have your fears ever borne out? Has there ever been any significant technical issues that have caused you to wonder if the experiment is in existential danger?
No, but the reason we had the four EVAs — you know what EVA means?
Two astronauts conducted four extravehicular activities, space walks, to replace part of the cooling system which had been designed for three years of operation. In AMS, we have a silicon detector, with 200,000 channels which dissipate 144 watts of power. To keep the temperature of the silicon detector constant (at 10+/- 3oC), the heat must be removed. In space, the heat has nowhere to go. We developed a two-phase (liquid to gas), CO2 cooling loop to dispel the heat. This is the first time anyone has used a two-phase CO2 cooling system in space through phase transition.
Sam, is space debris a concern for your research?
Yes, but that part so far has been very good. To protect the space station, NASA has a very effective system to avoid the debris.
So, you're fairly confident that this is well managed in the future.
Nothing bad has happened to us.
Sam, without the pandemic, where would you be right now? How would your day-to- day be different?
Well, I would be in my office. My office is just on top of the control room.
You're talking about where, at CERN?
At CERN. In front of my office there's a rather large window, and I can look directly to the entire control room which monitors all the detector systems of AMS in space.
The AMS has been doing amazing things for nine years. Can you give a sense of what a very productive day looks like versus an unproductive day? How do you know when the AMS is really sending back quite valuable data?
We check all the time. There is a group of people constantly checking the quality of the data 24 hours a day 7 days a week. Everyday is productive because unproductive days means you are in trouble - the detector is not working. It's different from the accelerators. As I mentioned in the beginning, the Space Station doesn't stop. The Space Station orbits the Earth every 93 minutes continuously without stopping. AMS is always there transmitting data.
How do you know that you're receiving new information? What's new that can come to the AMS day in and day out for all of these years?
For this you have to wait and analyze, because the system has 300,000 channels of information about each passing particle such as coordinates, pulse height, timing and temperature information. Everything has to be taken into account. We have a massive computer network mostly at CERN, some in the United States, some in France, some in Germany, some in Taiwan, and some in China. Every participating country will analyze the data at the same time.
What are some of the advantages of working on such a multi-national project?
You can do things carefully. You're not restricted by resources. Also, in an ideal case, of course, if you're clever enough, you do things by yourself. Such is not the case, because everyone's ability is limited. You have the collaborations because of necessity. Also, it's a good thing to work with people you respect. Most of the people who work with me have been collaborating with me for more than 20 years. Some of them, 40 years already. It is very important when you lead a collaboration to realize you have not done everything by yourself. You need to give credit to the people who have made important contributions, otherwise, nobody will work with you.
You have to be generous and humble.
Yes. Respect for your collaborators is really the most important thing to ensure their contributions are recognized.
Sam, is there an overall concrete goal that is understood that if the AMS reaches that milestone, it will be sun-setted eventually, or do you know not know, eventually in the long term, what the AMS will discover, and that alone is reason to keep it active for as long as it's able to bring back data?
We began to see some indication of heavy antimatter. We have a few signals, and we need more data to see that this is not due to something we did not understand. We did many checks of what we found – so far, we cannot find the reason that this signal is due to an instrumentation effect. We need to collect more data to see how many kinds of heavy antimatter nuclei we can find.
Sam, what are some of the major theoretical implications that come out as a result of AMS?
I do not know. There are many theories. I think it's correct to say you can adjust the parameters in any model to fit one AMS result, but the same set of parameters cannot explain all the other results. I think we have a long way to go to find the correct model to explain all the AMS results which have an accuracy of approximately 1%. It is most likely that AMS data will require a new comprehensive theory of charged cosmic rays to be developed.
Sam, you mentioned earlier that you see large accelerator programs on the ground as being complimentary to this project. In what ways are major telescope and satellite projects complimentary to AMS?
Telescopes measure light rays. We measure charged particles. They're totally different things. The results of telescopes have made fundamental contributions to our understanding of the cosmos. The existing satellite experiments use non-magnetic calorimeter techniques to measure the energy and value of the charge of the cosmic rays but cannot measure the momentum or sign of the charge. So satellite experiments are important but different from AMS which is a magnetic spectrometer.
Do you see a next generation of AMS? Do you see opportunity for a new experiment with new technology doing things in the long term that AMS could never achieve?
Yes. My colleagues in Germany, under the leadership of Stefan Schael of Aachen University, are thinking of building a very large AMS called AMS-100, with high temperature superconducting magnets, and going to the Lagrange point.
What does it mean to go to the Lagrange point?
The Lagrange points are locations where the gravitational forces between the Earth, Sun, Moon and other planets in our solar system balance. This means there is zero gravitational force on the instrument. Also, the environmental temperature is fairly low so you don't need a cooling system for a high temperature superconducting magnet. AMS-100 is a good experiment.
What is your feeling of the long-term prospect of all of these governments continuing to support this research? Do you feel good about that?
I have not heard any negative feedback from any funding agency. In fact, recently, three well-known groups, one from the Moscow Engineering Physics Institute (MEPhI), and one from Oulu, Finland, and one from Kiel, Germany, joined us. The reason people join is because they realize this is a precise instrument probing the unknown. Physicists join AMS because the results are interesting.
Sam, if you ever have the opportunity to testify before Congress, again, in your capacity as a senior scientist and an eminent physicist in this field, with the goal of ensuring ongoing American support of these projects, what would you say to that broad audience in Congress that might not understand the specifics of the physics that you're working on, but would appreciate how this work adds to our understanding of the universe? If you had that opportunity, what would you say in support of ongoing government funding for this and future projects?
The advancement of science is driven by human curiosity. 200 years ago, we thought the Earth was flat and the Earth was the center of the universe. After 200 years of scientific research, we realized we're not in the center of the universe, and our existence is an accidental thing. If you don't do research, you would never know.
When you say our existence is accidental, that's to say you believe there's no creator of creation.
I never thought about that. In the 20’s and '30s, we studied quantum mechanics and atomic physics without which we would not have modern day communication, computation and information technologies. We built accelerators in the '50s and '60s. At that time, it was for pure research, and now we use it for medicine, for producing radioactive isotopes and for energy sources. From discovery to application, there is sometimes a time lag of many years. If you don't do research, you will not know how it is possible to improve life on Earth. If the United States does not support basic research, other countries will support it. In the last 100 years, the U.S. has supported research, and this has made the U.S. the world leader in science and technology. It really would be good if we continue this leadership.
Sam, I'll ask you a question that's pure speculation, and of course, you can't know about it. I wonder, if 200 years ago we thought the Earth was flat, do you think it's possible that in another 200 years, scientists will look back at 2020 and think about how primitive our understanding of the universe was? It's another way of asking, how little do we really understand now?
I totally agree with you. When I started doing physics, electrons, pions, and protons were the basic elements of the universe and the most interesting subject in particle physics. No one thought that, after half a century, the basic elements are quarks and leptons. After another 200 years, our views may be completely different. Curiosity is what drives the scientists forward and society benefits.
So, there's so much more that we don't understand, of course.
Yes. If you don't probe, you will never know.
So, what, in your mind, are the biggest questions that remain unanswered?
I normally don't think about this. I normally concentrate on my experiment. Since Dick Feynman, Pief Panofsky, and I.I. Rabi all passed away, I now discuss my research with the Directors General of CERN (Herwig Schopper, Rolf Heuer, Fabiola Giannoti). All of them are very good physicists with extraordinary vision. I also occasionally discuss our physics results with Steve Weinberg, Dan Goldin, and William Gerstenmaier. But most of the time, I'm alone.
Sam, looking back on your career, do you see any one particular research project that was more fundamental than any others, or do you tend to look at everything as one large story of all of the experiments that you've been involved in?
20 or 40 years from now if people will look back at what I have done, the only thing that is worth mentioning is probably the AMS experiment. The challenge, to put a magnetic spectrometer in space, was really quite difficult. No one would have thought it could be done before we did it and all our results are completely unexpected.
So, long term, you see that achievement as more fundamental, even than anything else you were involved in, because of the difficulty.
Because of what we have seen was so different from what could be seen before. Difficulty is something else. You can measure the distance from MIT, from my office, to the surface of the moon to an accuracy of a micron. That is very difficult, but has no meaning, mainly because the result cannot improve our understanding of the cosmos.
So, this is to say that perhaps all of your discoveries, and your involvement in discoveries in the world of particles, was incremental, but your contributions in this area were a quantum leap, if you will.
Quantum leap is too much. I would say, unpredicted. Nobody knew that cosmic rays behaved like the AMS has observed. No one has measured them with such accuracy. As I mentioned, in comparison of AMS resolution with that of balloon experiments, it is like looking at an object with your eyes and looking at it under a microscope, you see different things.
Sam, you mentioned before what a pleasure it is to work with all of the post docs in this project. What is some general advice that you have for some of the most promising young physicists working in the field today? What are the kinds of things that they should be looking out for over the course of their careers in the future?
Before I do that, let me tell you a story. I was doing an experiment at the ISR, Intersecting Storage Rings, at CERN. There was a young post doc. I think he received his PhD, at age 16 or 18. When he came to work with me as a post doc, it was before he was 20. After working with me for two years, he came to see me and said, "I'm not interested in physics. I find it's boring. I want to do something different." So, I told him, "You should leave right away. What are you interested in?" He said, "Medicine." I helped him to get into medical school, and now he's making a major contribution at the Mayo Clinic in Minnesota. To do this type of physics as a post doc, you really need to think this is the most important thing in your life. Most of the time is collecting data, monitoring instruments, and unless you truly appreciate the significance of the unique physics results and think this is the most important thing you want to do, you won’t be satisfied. Otherwise, it is perhaps best to find a different career.
How was that advice taken?
It worked out pretty well. I should add that coming to work with me often means you will get a Ph.D. degree in a short time, two or three years. Indeed, normally I don't keep students for a long time, because what they can learn from me, I consider very limited.
In what ways has your long-time affiliation with MIT been useful for your research in experimentation?
MIT has been very supportive. After I worked in Hamburg, the director of the German laboratory, DESY, Willibald Jentschke, asked me whether I would accept a position as Director of Research and become a professor in Hamburg University. At that time, it was very difficult for a foreigner to be a professor in Germany. He said they would be willing to go to Bonn, the capital, and petition for this. I told them, "No, thank you very much. I'm American. I would like to go back to the United States." Jentschke said, "I will help you find a job." So, I had many offers. All the offers were with tenure. The only offer without tenure was from MIT. The head of the physics department at MIT, Viki Weisskopf, told me, "We don't offer Associate Professorships with tenure." At that time, I had no concept of what tenure was. It also meant nothing to me. I did make a request to Viki Weisskopf. You have heard about Viki Weisskopf. Do you know who he was?
Of course. I know one thing about him more than anything was the culture that he fostered of support and collaboration that made so many different kinds of physicists so comfortable in doing their work.
Yes. I had a conversation with Viki Weisskopf, and he said, "This is fine. Tenure has no meaning to me." Basically, I didn't understand what it meant. "But I want to have a condition, and that is you will allow me to choose my experiment, no matter where the location is." This is how MIT has always supported my working in Europe. After a few months, I was at a faculty lunch. After the lunch, most of the faculty went to a meeting, and I was not invited. It was explained to me that it was only for tenured faculty members. Then I realized what it meant.
You finally got it.
Then, I told Viki, now I understand what tenure means, and during these few months I was at MIT, I had some papers published in Physical Review Letters that were considered important. Also, I had not yet said “No” to all the other universities who were interested in me. But Viki said, "Well, don't move" and within two months I received tenure and shortly afterwards I was promoted to full professor. So, since the beginning, MIT has always been very supportive of my research.
I'll ask the same question of CERN. In what ways has your affiliation with CERN provided an ideal backdrop to conduct your research?
I suspect some people over the years at CERN, such as Herwig Schopper, Fabiola Gianotti, Rolf Heuer, Robert Aymar, Steve Meyer, Franco Bonaudi, and others have found my work interesting and have actively supported us. They have provided the facilities, technicians, and enormous amounts of computing time. CERN also have provided logistic and administrative support and built a special building for the AMS control room, even though we are only a “Recognized Experiment” and not a CERN Experiment. Of particular importance, CERN has provided two extraordinarily gifted persons: Dieter Schinzel and Corrado Gargulio, to help us assemble and test AMS before its launch. Both of them, together with Trent Martin and Ken Bollweg of NASA, possess unusual insight and experience in precision instrumentation which was key to the success of AMS.
Sam, do you look back at your career as having major phases? Do you see a particle phase, and then a cosmological phase, or do you not tend to make those divisions?
The closing down of the Superconducting Supercollider (SSC) was a very important phase change in my career.
Meaning that had the SSC gone through, it's likely that you never would have gotten involved in AMS.
Most likely. We'll never know, but most likely.
Right. So, it's such an interesting topic of conversation what would have happened if the SSC had been created. Had it gone through; what do you think you would have done?
I do not know.
But you do know that whatever it was, it would have been big enough to occupy you.
I would imagine that the 2000 American physicists working on LHC now probably would have stayed in the U.S., at Waxahachie.
Sam, what are some of the major disagreements in the world of experimental physics over the years, and where do you see yourself situated among any of those differences in opinion?
I do not know. You need to be more explicit. If you give an example, I would be able to tell you.
I guess I don't want to be specific in the sense that if you can't think of anything in particular, that's what's significant for your answer, if there are no major differences of opinion that you feel are important.
No. Also, I'm not sensitive to that. I should like to mention that most of my major experiments, such as the J particle experiment at Brookhaven, the AMS experiment on the Space Station, had strong opposition from the community because most of the physicists thought they were too difficult to be carried out. In addition, many people considered the results of these experiments, if any, would be meaningless. I have learned to distance myself from controversies and concentrate on what I believe in.
And perhaps you learned early on in life from your parents and your family experience, young, that politics has its place, and science has its place.
With the exception of Panofsky's program committee at SLAC, I have seldom served on scientific program committees.
Is that another way of saying that the regard in which you held Panofsky, that you made this special exception?
I find it's difficult to say no to him. He's was a very good person. Both Panofsky and Rabi — and Feynman. How was your interview with Glashow? How did it go?
Oh, it was wonderful, of course. We had a great time. Just like with you. Sam, I think for my last question, I want to ask you something that's forward looking. That is, we've talked so much about the broad range projects that you're involved in, and these will go on for a long time to come. But I want to ask, specifically for you, time can be a limited resource, finances can be limited resource, what are the most important things for you, personally, that you want to accomplish for the rest of your career?
Fortunately, there's no retirement at MIT.
And physicists never retire anyway, I've learned.
They never retire. I spend all my time watching the performance of AMS and analyzing the data of AMS. I've always limited myself to one experiment at a time. Many physicists are able to do several experiments at the same time. I've never been able to do that. I always dedicate my time and energy to doing one thing at a time. As long as I'm able, I'll just concentrate on AMS.
Sam, is it fair to say that physics has kept you young?
Keeps me curious. That's why many people find me boring. Besides physics, my other knowledge is very limited.
Well, that has certainly served the field of physics very well, that you have decided to concentrate all of your powers in this area. Well, Sam, on that note, I want to say, I have not found you boring whatsoever. I have been transfixed throughout this interview, and I'm honored that you've spent this time with me. To state the obvious, your recollections and your stories over your many decades in the field will be a truly tremendous and unique addition to the historical record. I'm just so happy that we connected, so I really want to thank you for our time together.
Thank you. Particularly interesting for me was you asked about my childhood. I had forgotten about that for a long time.
That's where it always starts.
Okay, thank you sir.