Yifang Wang

Zierler:

Okay. This is David Zierler, oral historian for the American Institute of Physics. It is September 14, 2020. I am absolutely delighted to be here with Dr. Yifang Wang. Yifang, thank you so much for joining me today.

Wang:

Thank you. Glad to do it.

Zierler:

Thank you. So, to start, Yifang, would you please tell me your title and institutional affiliation?

Wang:

I’m a professor and the Director of the Institute of High Energy Physics, Chinese Academy of Sciences.

Zierler:

What other connections does the Institute have? Is it connected with a university? Is it an arm of the government? What are the broader connections with the Institute in China?

Wang:

Well, it’s an institute under the Chinese Academy of Sciences, which has something like 100 research institutions, and we are one of them.

Zierler:

I see. Okay, Yifang, let’s take it all the way back to the beginning. I’d like to hear a little bit about your parents. Tell me about them and where they are from.

Wang:

My parents are from a city called Nanjing. It’s in Jiangsu Province. They were not born there, but they worked there when they were young, so I was born in Nanjing. My father is a doctor of Chinese medicine, and my mother is a nurse.

Zierler:

Tell me a little bit about your education growing up. What kind of school did you go to?

Wang:

I went to schools in Nanjing from elementary schools to middle schools all very much close to my home. Then I went to university, the Nanjing University, which is also something like less than 5 km from my home, so from my elementary school, middle school to high school and all the way up to university in the same area, say, not more than 5 km in diameter.

Zierler:

Now, your father being a doctor and your mother being a nurse, you grow up in a science-oriented household. Did you always know that you wanted to pursue a career in science?

Wang:

No. I have to say that when I was very young, I actually had no idea what I should do. That was actually during the Cultural Revolution, so actually, for young kids, we all knew that when we grew up, we were going to become either a farmer or a factory worker. We were actually not able to choose our career at that time, but things had been changed dramatically when I was 14 when Deng Xiaoping took power and decided that all the young kids or students could go to university as they wished. So, that completely changed our life.

Then, of course, at that time I did not have really, say, a dream of what I would like to become, but we all knew that we had to be good at school in order to enter university. So, we didn't have really a motivation, but we all knew that we had to do a good job in school. At that time in schools, you had to learn math, physics, and chemistry, etc. So, I decided to go to physics because I’m not very good at chemistry and biology because those—you need to remember a lot of things. I’m not very good at it, so I think that’s not something I would like to do, and same for the medicine. Indeed, my father told me that “You may choose to become a doctor if you wish.” Then I say, “No, I don't like to remember all these kinds of strange names.” While for physics, you don't have to remember. I mean, there’s logic there. You can just derive and very little you have to really use your memory, so I decided to go to physics.

Zierler:

Yifang, tell me about the entrance exams that you took in order to be able to go to college.

Wang:

Oh, at that time there was a national exam, so everybody had the same exam you had to take, and then you got your final score. According to your result, you choose, say, from a good university all the way down to a not so good university. My score was not terribly good nor terribly bad, so I managed to go to the Nanjing University at that time, which was actually between the top five to top ten universities in the country. So, not terribly bad, but also not number one. [Chuckles]

Zierler:

Were you able to live at home? Was it close enough to continue living at home with your family?

Wang:

No, I didn't. Of course, I could. It’s only, say, 5 minutes by bike, but I decided to stay in the university dorm with all the classmates because I believed that was better. I mean you don't have to stay with your parents all the time. So, I thought it was better to stay with my friends, my classmates, and so on.

Zierler:

Now, how does it work there? Did you declare the major in physics right away, or is there a general education requirement first?

Wang:

No. When you choose your university, you have to choose your major also, so I chose physics. Of course, physics is the most difficult and mostly wanted subject. If you choose, for example, geology or biology, the requirement of the score was not so difficult or as stringent. So, you had to declare.

Zierler:

Yifang, pardon me one second. I have to close the window. It’s noisy. I’ll be right back.

Wang:

Okay.

Zierler:

Okay. Yifang, tell me a little bit about the lab work that you did in physics at university.

Wang:

I think in my time, of course we had a little bit of the lab, but that’s only in a very low level for the education purpose. Indeed, I hadn't done any real, say, lab works or research when I was a university student.

Zierler:

Do you get close with professors? Do you start to work on a one-on-one basis with professors as an undergraduate, or you still have to wait until graduate school for that?

Wang:

In the last semester before my graduation, we had half a year kind of lab work, and we had to work with the professor to have a “research” topic, which was of course very simple, not so difficult a topic. We got the chance to work with a professor to do some research. That was a requirement. Every student was required to have some lab work or some research before the graduation for half a year.

Zierler:

Yifang, as you were learning more and more about physics in college, what kind of physics were you becoming most interested in and what kind of physics did you realize you had the greatest talents for?

Wang:

I think it’s hard to say. When I was chosen to be a student of the physics department, I was already assigned to the major of nuclear physics, so indeed, there’s no way to choose from. And of course, when I learned more and more, indeed, I do like nuclear physics and also particle physics. However, at that time there was very little subject of particle physics taught in China. Nuclear physics is something which it’s closest to. Indeed, I like it, so it is, in the end I would say, the best choice for me, although it was done by somebody else, but I think it was the right choice.

Zierler:

Now, why is the system such that nuclear physics would be chosen for you?

Wang:

I’m not sure. I guess it was random because at that time in our physics department, there were four different majors you could choose from. They didn't ask us to choose, but they just, I believe, randomly distributed to people. I have no idea how the system works. I was informed that “You are a nuclear physics major.” [Laughter]

Zierler:

Yifang, I’m curious to hear your perspective on how international your understanding of physics was in college. In other words, were you aware of what was going on at places like CERN or at SLAC, or was it a very Chinese-centric approach to physics where you really only learned about things that were going on in China as they related to physics?

Wang:

I have to say I knew very little about international kind of physics work. Of course, we had some visitors from time to time. For example, I remember very clearly that we had Madame Wu visit our university several times. We heard her speech or presentations, and she actually told us what she was doing, what she did in the past. But I would say more in the past than the future. We really didn't have any, say, physicists from CERN or from SLAC to give us a talk, at least not in my memory. I never heard of this. Of course, we heard the names of Sam Ting, T. D. Lee and C. N. Yang, and so on, so we know what they did, but we really didn't know what the exact research they were doing, or very little.

Zierler:

Yifang, I’m curious with nuclear physics. Did you ever think about pursuing a career with the military or with the government in terms of using your degree to increase Chinese military capacities?

Wang:

I think in the ’80s we all had the kind of mind that the military kind of research was less and less important. So, of course, most of us didn't want to go to that kind of, say, industry because we knew it was a declining industry. It was not our choice, I would say. Of course, we knew there was a great past, but we all knew that it was not going to be a great future. [Chuckles]

Zierler:

When you graduated, what did you want to do? What opportunities were available to you?

Wang:

We had a few choices. First of all, graduate school where you can learn how to use the nuclear technologies for applications, say, in industry and in medical kind of devices and so on. We also had people going to a nuclear power plant, and we also had people going to some research institutions in other cities, other places. But my first choice was to become a graduate student, again in the same university, in Nanjing University where I can use the nuclear technologies to, say, measure some kind of useful parameters such as isotope types or densities for applications.

Zierler:

So, you went on straight to graduate school from undergraduate in Nanjing.

Wang:

Right, right, right. It was about to happen, but not really, because then I was chosen by Sam Ting to go to CERN, so I didn't pursue the graduate study in Nanjing University.

Zierler:

So, that was the plan, but then Sam Ting reached out and that’s how you got to CERN.

Wang:

Right, right, right.

Zierler:

How did you first meet Sam?

Wang:

At that time, we were told by the University that we had a chance to be selected by Sam Ting, so we went to an exam. First of all, a written exam and presumably I got a reasonably good result. Then we were told that we would have an interview. We went to Shanghai and then we were interviewed by Sam Ting, so that was the first time I met him.

Zierler:

What was it like to interview with Sam when you first met him? What do you remember from that?

Wang:

Well, very interesting, I would say. Of course, we heard his name and we also saw his pictures from time to time in the newspaper, but for the first time to see him in person, it was a very interesting experience because actually [seeing him], he was, say, much younger than his age. So, at least for us, it was a surprise because we thought he must be, say, much older than he appeared when we saw him. [Laughs] And, of course, he asked us questions, I mean, the kind of questions we…Indeed, some can and some cannot answer. But in the end he chose me for whatever reason. He just decided to pick me. [Chuckles]

Zierler:

Yifang, what was your sense of what Sam’s research at CERN was? Did you have a good idea what you’d be getting involved with when you accepted his offer?

Wang:

Yes. We all knew that he worked on particle physics, and this is something that we didn't learn. We had no idea exactly what it was, but we all knew that particle physics, or high energy physics, is something very difficult and very costly and it’s not going to be something that China could do. If we chose this direction to work with him, when we went back to China, we probably couldn't find a job in China. That was the kind of sense that a lot of people had. Of course, I had some hesitation, but then I thought that this was really a great chance to work with the greatest scientist of our century, I should not lose the opportunity. So, I decided whatever the future is, I should go for now. [Laughs]

Zierler:

Now what kind of government support or administrative support did you need in order to leave China and go to CERN? Did somebody need to sponsor you? Did you need approval from the government or your university? How did that work out?

Wang:

To be honest, I don't know exactly in detail. I just worked with the University; everything had been sponsored by the University. So, all that I needed for the applications, passport, visa, and so on, the University actually sponsored me. They did most of the administrative work for me.

Zierler:

When did you arrive at CERN?

Wang:

I actually arrived first in Italy, in Florence, because Sam Ting had his L3 experiment which consisted of something like 40 or 50 institutions from all over the world, one of which is the University of Florence. So, he picked out these five to ten students a year and distributed them to different institutions of his L3 experiment. For whatever reason, I was chosen by somebody to be in Florence, so then I first went to Florence in October 1985. I stayed there for several months, and the first time I went to CERN, I believe was in the beginning of ’86, a few months after I arrived in Florence for test beam experiments. I went there to help on the test beam.

Zierler:

Now Yifang, before I ask if this is your first time out of China, I must first ask is this your first time out of Nanjing as well?

Wang:

No, of course not. I had been to other cities in China, Beijing, Shanghai, and so on. Of course, this was the first time I was out of China.

Zierler:

And I’m curious. What were the language expectations? I’m assuming that once you get to Europe, you're going to be expected to speak languages other than Chinese.

Wang:

Yes, of course. We learned English from school—actually, from the middle school, the first year of the middle school. So, indeed, before I entered university, I had six years of experience of English study, and then I had four years in the University. So, my English, to be honest, compared to other Chinese students at that time, was reasonably good. But still I couldn't speak, even though I had ten years of experience of English study. [Laughs] So, I still had a lot of difficulties to talk to people in English, and on top of that, in Italy, obviously you can imagine that I had to learn some Italian because in the group and in the street, everybody spoke Italian, so I cannot just speak English.

Indeed, before I went to Italy, the University knew that I had to go to Italy. We actually had Italian students there in the Nanjing University, so the University paid me to have one-on-one kind of oral study with Italian students. So, I studied Italian with her for roughly half a year. That was actually a very good beginning; otherwise, I could not have started from…I couldn't really speak Italian there. When I arrived in Italy, the University of Florence also paid me to study Italian for another half a year through some language schools, so indeed, after this kind of training, I could speak some Italian.

Zierler:

How long were you in Italy?

Wang:

In total, six years.

Zierler:

Six years. Did you go back and forth from there to CERN?

Wang:

Yes, yes, yes. So, to be honest, I think in those six years, half of my time was actually at CERN.

Zierler:

What were the major projects that you were involved with? First, let’s talk about Italy and then we’ll get to CERN. What were the major projects in Italy that you were working on?

Wang:

I was working on the hadron calorimeter of the L3 experiment. At that time, Florence was responsible for the so-called muon filter of the hadron calorimeter, in other words, it’s the tail catcher of the hadron showers in the hadron calorimeter. So, we were working on that from the simulation, construction of the detector, readout electronics, the test beam, and so on. Most of my time in Florence was devoted to this calorimeter construction. Of course, I had to follow courses, and also, before the detector installation, to work on the software like data acquisition and monitoring. Mostly, my time was on the detector.

Zierler:

Who were some of your major collaborators in Italy?

Wang:

It was Professor Piero Spillantino, Professor Bianca Monteleoni, and Professor Anna Cartacci. These were the three main advisors. Of course, I worked with a lot of, say, classmates, students, and also the post-docs. They also helped me a lot for my time in Florence.

Zierler:

Now, you're operating essentially as an undergraduate—I mean, a graduate of college. You're not yet in graduate school.

Wang:

No, I was in the graduate school.

Zierler:

Oh, so this is—it’s also—

Wang:

I mean, they recognized my graduation in Nanjing University.

Zierler:

So, this is part of your graduate work, what you're doing in Italy.

Wang:

Yes, yes.

Zierler:

What is the home institution for your graduate school?

Wang:

University of Florence.

Zierler:

Oh, I see. I see. And these are the people who are also on your committee who you just referenced?

Wang:

Yes, yes.

Zierler:

Aha. I see. How did you go about developing your dissertation? Was it directly related to this research?

Wang:

Yes, this was a part of my dissertation. When L3 started the data taking in 1990, I actually spent more of my time at CERN working on the data analysis. So, I’d been working on the search for excited leptons, including excited electrons, muons, taus, and also neutrinos. So, that was actually my main thesis topic, the search for excited leptons.

Zierler:

Now, how did you develop that interest in excited leptons?

Wang:

I think just by chance. I was there during the L3 time. Very often in the corridor I talked to different people, and one day, a young faculty from the University of Naples, said to me this topic. He was actually one of the analysis coordinators of the L3 experiment, he told me that, “Oh, look. This topic, you may be interested. Nobody’s working on it. Why don’t you just work on it?” Then I said, “Okay. Interesting.” I took it. [Laughs]

Zierler:

So, most of your dissertation research actually took place at CERN.

Wang:

Right, right. For the data analysis, yes.

Zierler:

What were some of the experiments that you were relying on for the analysis of this data?

Wang:

We just took the data from L3, it was all the L3 data we did this analysis. Yeah.

Zierler:

Can you talk a little bit about L3—how it started, how well developed it was by the time you started working on the project?

Wang:

L3 is one of the four experiments at LEP. In 1985, when I started my study in Europe, I think L3 had been already well established. The detectors had been designed and the tasks had been distributed to different universities, so Florence already had the responsibility, as just mentioned before, of the hadron calorimeter. By the time of 1990, data taking started, and everybody tried to get their analysis topics by themselves. That was not, say, organized, so everybody tried to get their own research topic on the data analysis. So, I picked out one. I did that. For the detector part, say, before I entered everything had been set more or less.

Zierler:

Yifang, if we could zoom out a little bit, what are some of the larger research questions that L3 and the related projects are seeking to understand?

Wang:

I think there were a few hot topics at the time. First of all is the Higgs search, so a lot of people were working on the Higgs search. Of course, nobody had seen it because there was not enough energy to produce the Higgs at this accelerator. Then there were people working on the number for neutrinos. That was the hot topic because we knew that at that time we had three generations of neutrinos, so a very obvious question was: does there exist a fourth generation of neutrinos? That involved a lot of people working on the cross-section measurement and so on. That was a hot topic, yeah. To be honest, the excited lepton search was not a hot topic. Not very many people were working on it.

Zierler:

[Laughs] But there’s also opportunity there for you to work on something that not many other people were working on.

Wang:

Indeed. So, once you did it, you became famous in the collaboration then. I was a student; nobody knew me, but if you did this kind of research independently, then, of course, people notice you. So, in the end I think it was very good for me.

Zierler:

Yifang, what were some of the principal conclusions in your data analysis from L3 that informed your dissertation?

Wang:

We didn't see, of course, the excited leptons, so the composite model and also these types of new particles didn't exist. We set the limit of cross-section of mass and so on.

Zierler:

What did you want to do after you defended? What was next available for you?

Wang:

So, my next job was tau polarization because I finished this new particle search. I thought that I should work on something which really existed. I mean, new particles that don't exist—you cannot always be working on something which doesn't exist, so I thought I should do something real. So, tau polarization does exist. It’s standard physics, but it’s very difficult because from, say, detector design, a lot of people believed that the L3 detector could not identify the tau-hadron decays, so you were not able to measure the polarization. I did on this. I had a new method to identify the final states of tau decays, and I managed to measure the polarization.

Zierler:

Were you in close contact with Sam Ting at this point? Were you still working with him?

Wang:

Yes. When I was a student at University of Florence, I did this search for excited leptons, and then when I was on the tau polarizations, it was half and half. It was half of my time in Florence and half my time as post-doc. So, Sam knew that I should finish my thesis and I’m supposedly looking for a job. He asked me where I planned to go. I said, “No, I haven't decided on any opportunities,” and he said, “Why don't you come to MIT?” I said, “Okay, yes.” [Laughs] So, I decided to go. It was quite easy. So, I didn't even write any applications, real applications looking for a job; I got this offer. Then when I finished all the technical details of the thesis, I moved to CERN permanently to become a post-doc at MIT. Then I worked on the tau polarization and also the QCD studies of hadrons from jets.

Zierler:

So, you split your time equally between MIT and CERN at this point?

Wang:

No, almost 100% at CERN.

Zierler:

Oh, I see.

Wang:

Yeah. Most of the people at MIT are actually working at CERN. You don't have to stay at MIT.

Zierler:

Right. So, who were some of the people that you were working with at this point as a post-doc?

Wang:

I continued to work with people at L3, not really with people from MIT. Indeed, at MIT I was more or less independent. I just worked for myself. Yeah, I was of course reporting to Sam.

Zierler:

What were some of the major research questions that you were pursuing at this point?

Wang:

There were actually two questions. One is this polarization. I thought that was something interesting. It’s Standard Model physics, and people were trying to understand whether the Standard Model was actually correct in every detail of your data. So, we tried to measure this parameter. It’s one of the Standard Model parameters.

Then afterwards, I actually was interested to look for glueballs. I had the idea that the gluon jet should have a higher probability to have glueballs in it, so I was trying to look for glueballs in a gluon jet. That was actually a very difficult task, and nobody actually had done this before ever, and nobody even talked about this, even by theorists. So, I tried and in the end did not really see glueballs, but we managed to measure some of the neutral hadrons like pions and the etas, ?0, the etas, and so on in the gluon jet. We tried to analyze these kinds of QCD predictions and compare it with the data to see whether there was any excess.

Zierler:

What were your findings with this research?

Wang:

We found that the QCD and the Standard Model worked pretty well, so we didn't see anything strange. [Laughs]

Zierler:

It’s always good to confirm the Standard Model.

Wang:

Indeed. I was hoping to see something strange or new things like glueballs, but unfortunately, we didn't see anything strange.

Zierler:

Now, what might be some of the theoretical underpinnings had you seen something to challenge our understanding of the Standard Model?

Wang:

Well, the glueballs are always something people have been looking for, even nowadays. We didn't see them. It is actually a very natural, say, prediction of the QCD. You could claim this is still part of the Standard Model, but they have not been seen by experimental data. But it’s something very interesting. The question has not yet been answered even today.

Zierler:

When did you complete your post-doc? What year was that?

Wang:

It was 1996. So, I finished my PhD in 1991, and in 1992 I moved to CERN/MIT. It took me four years. During that time, also I worked with Sam Ting on the design of AMS. That was actually the very beginning of the AMS thinking, design, and also the construction. So, I worked on the design and the Monte Carlo simulation of the AMS. Then I realized that I’d been working at CERN and in L3 for more than ten years. It was quite long, and even as a post-doc it had been already four years; I had to do something different.

I looked around and indeed, I was looking for something, say, an experiment which was small enough so that I was able to put my hands on by myself initially because L3 was already something well defined when I entered. If you go to a big experiment, you always find out that things have been decided by someone else and you are not able to change or even able to know why it is this way.

So, I decided to go to a small neutrino experiment at Stanford, and there, actually this was at the very beginning. The group was very small; it was only 20 people. So, I believed that this could be a great opportunity for me to know the details of an experiment and also its idea, why the experiment was such. I also could do whatever I wanted to change the design, to change the construction, so that was my thinking at that time. I decided to leave, so I told Sam Ting that I would like to leave. Firstly, he thought that this was not a good idea and he asked me to think again. After a week or two, I went back, saying, “Sorry. [Chuckles] I made up my mind. I would like to leave,” so he said, “Okay. Yes.”

Zierler:

Sam wanted you to stay on with AMS.

Wang:

Right, right.

Zierler:

Can you talk a little bit—before we get to Stanford, what were some of the major goals of AMS? What was it looking to achieve?

Wang:

The main goals of the AMS were looking for antimatter because in the past, we had a lot of experiments in space, but never with a magnet. If you have a magnet, you can determine the charge and then once you know the charge, you can determine whether this is matter or antimatter. We always had this mystery that we have no antimatter in the universe, so the idea is that maybe you didn't have a chance to detect it. If you have a detector with a very high sensitivity, maybe you can see them. They may exist there. So, that was the main idea.

Sam decided to have this magnet made of a permanent magnet. In the past, there were ideas making a superconducting magnet. It was extremely difficult, and they all failed, so that was the reason why there were no magnets. People all thought that a permanent magnet was too heavy, too low the field strength, and that you shouldn't use that. Sam came up with the idea that you can have a permanent magnet in space with a reasonably good or lightweight and reasonably strong magnetic field, so that was a great idea. In the end, we had this permanent magnet in space for the first time, so this was really, I would say, a great breakthrough.

Zierler:

It must not have been easy for you to say no to Sam Ting, and so what was so exciting about Stanford that convinced you that this was the right move for you?

Wang:

First of all, this was a new experiment. Neutrino was interesting—a lot of ambiguity, a lot of different experimental results—and so I believed there could be some chance. Also, to be honest, I really liked to change my life a little bit. I didn't want to continue my life in one particular form for more than, say, ten years. I thought I didn't like it. [Laughs]

Zierler:

When you got to Stanford, was this a second post-doc?

Wang:

Yeah, indeed.

Zierler:

Who were you working with there and where were you working?

Wang:

I was working with Giorgio Gratta. He was a new professor there at Stanford, and he was actually collaborating with Felix Boehm from Caltech on this Palo Verde reactor neutrino experiment, and that was the idea started in 1992, I believe. So, by the time of 1996, it had already been pursued for four years, but went pretty slow, to be honest. So, Giorgio joined the group and he had different ideas. He wanted to push the experiment in a slightly different way, and of course he wanted people to join. I knew him before, so he wanted me to join. I didn't really look for a job, which is to say good pay or high level of position and so on. I just wanted to look for a good experiment, a right experiment, and I believed this was a good one, a right one. So, of course, this was still a post-doc position, but I liked it.

Zierler:

Now, this was your first time in the United States on a sustained basis?

Wang:

Yeah, yeah. Right.

Zierler:

What did you think of California and Stanford when you got there? What were your first impressions?

Wang:

Well, indeed, I had a visit to California before and indeed, I liked very much the atmosphere and also the university. I also visited Stanford University before, so indeed, the atmosphere was something I really admired. That’s also one of the reasons I chose to go to Stanford. I liked the place.

Zierler:

Can you talk a little bit about how you got your research started at Stanford? How far along was it before you got there, or did you really help start it from the ground up?

Wang:

When I went there, the experiment already had something like four years of history, so people had been working on it. But it was, say, designed, organized, and also to be constructed, we believed, slightly different from, say, high energy physics community. [Chuckles] It was mostly, I would say, nuclear physics community. So, it was very much…of course, a lot of things are similar, but there are some cultural differences. So, we started differently. For example, we had a very different Monte Carlo simulation. We had a different way of thinking to analyze the data, and we had our own way of designing the trigger and the electronics. So, of course the concept was still the same, but the way to realize the concept was very different.

Zierler:

Yifang, I’m curious if at some point you thought that you might make a career, a long-term career not in China, but perhaps in the United States or Europe. Can you talk a little bit about when you might have been thinking along those lines, or did you always know at some point that you would return home?

Wang:

To be honest, I actually was open to all the possibilities. I never made my mind up to the point that I decided to go back to China. So, indeed, when I was in Europe, I’d been looking for jobs (before Stanford) in different places. In the end, I chose Stanford, of course. When I finished my experiment at Stanford, actually, I had been looking for jobs here and there, but I didn't find anything ideal. Either the experiment was not ideal or the job itself or the place or many other things—so I never found anything which was just perfect and everything fit my thoughts or my hope.

Then, of course, Beijing, the Institute of High Energy Physics gave me an offer and they told me that there are opportunities. Also, they were talking about the possibility to shoot a neutrino beam from J-PARC to Beijing. I thought this was a great idea, and I made my own calculation and it attracted me a lot. I thought this was a great experiment, so I came up with a design of a detector and so on. It could certainly measure the CP phase of neutrino mixing, and so on. All this could be perfectly measured, so I thought, this is a great experiment. I should go. Then I decided to go to IHEP for this experiment. Of course, the experiment didn't realize for many other reasons.

Zierler:

Yifang, before we get back to Beijing, I’m curious. How did your research at Stanford end? What were some of the principal conclusions that you and your colleagues came to?

Wang:

Yeah. We were looking for the reactor neutrino oscillations. At that time, actually nobody knew what the Δm²₂₃ is. What does the atmospheric neutrino anomaly in the neutrino oscillation parameter space look like. It was all blinded. So, at that time, reactor neutrinos could reveal the Δm²₂₃ and also sin²2θ₂₃. But, of course, we didn't see anything. It was the wrong baseline and the wrong energy. Nowadays we realize that, and this is actually a right distance, a right energy for Δm²₁₃, not for Δm²₂₃. But at that time, we didn't know, so the experiment at Stanford concluded that there is no neutrino oscillation. That’s it. I mean, we didn't see anything.

Zierler:

How did the connection back at Beijing happen? Did you get a call? Was Sam Ting involved in this? How did that all come together for you?

Wang:

I knew these people when I was at CERN. These are the same group of people working with Sam Ting on L3. So, I knew them very well, and we had contact from time to time. Also, I believe in 2000 or maybe 1999, there was a conference at SLAC, lepton-photon. There was a large group of Chinese physicists that went to this conference, and of course I knew them before, so we had dinner together. We were talking about…and they actually tried to recruit me and talked to me about all the possible futures in Beijing. So, then I accepted. I thought that was a good opportunity.

Zierler:

Yifang, were you paying attention during your many years away from China some of the developments in China in physics? Were you sort of staying on top of the literature, or when you came to Beijing, this was essentially a whole new world for you that you had not been involved in for a long time?

Wang:

This was a group of people that I knew well, for more than ten years, so even though I didn't have close contact with them all the time, it was enough to say hello every two years. So, we’d known each other for quite some time. To be honest, it was not a total surprise, but also it was not something that I knew very well. Of course, there were small surprises here and there, but China is my home country, I had gone there every two years to see my family. So, it was not a surprise for me in many ways. I did talk to people.

Zierler:

Yifang, at this point I’d like to ask a more general question, and that is the extent to which you see physics in national terms as a competition. In other words, in the United States, when the SSC was not built, there was concern that Europe would become the leaders in high energy physics or now that China is one of the places where perhaps the ILC will be built, that China might become the leader in this area of physics. Because of your background and the fact that you’ve worked in China, in the United States, and in Europe, do you tend to see these things in national terms and in competitive terms?

Wang:

I think both. Of course, sometimes we are in the position to compete with each other, but in most cases, we also have to collaborate. I’ve been working in China, working in Europe, working in Japan. Actually, I worked in the KamLAND experiment in Japan when I was at Stanford, and I worked in the United States. So, I actually know people everywhere, and we know that being a scientist, we actually wanted to pursue the science itself. We really want to have, say, good knowledge, a good understanding of the nature as a human being, so not necessarily, say, this is only good for China or only good for the United States. But of course, sometimes you need a little bit of competition because without competition, you never get funding from your government, right?

Zierler:

Right! That’s a great point.

Wang:

Being a scientist, I think when we come to the real work, we collaborate. Of course, even within the collaboration, different groups have some competition. I think this is good. You cannot say that we don't want to have any competition. In the group, having different groups compete on the same topic sometimes actually pushes things much faster and makes your analysis and results much more reliable, more believable. But on the other hand, we also have to collaborate just like a collaboration that we always have to work together in a kind of fair competition.

So, in the future, my dream will be that every continent like Europe, China, United States, Japan—everybody will have their own big project, big accelerators for different purposes. So, we compete in the one way, but also, we collaborate on the other way. In this case, we have a good development in all the different regions, and we are able to pursue with our own government to move quickly. I mean, if you don't have competition, your government is not going to move quickly, so this is not a good thing. Of course, now in high energy physics as accelerators become much more expensive, a lot of people believe that it’s hard to have four large machines in the world. But I think if we are not able to have four, we need to have at least two to compete a little bit with each other. Otherwise, if the world was left with only one machine completely dominated by, say, one country or one region, it’s going to be very bad for our science.

Zierler:

So, Yifang, on that note, when you got to the Institute in Beijing, what were some of the major projects there that embodied that mix of healthy competition, but also collaboration? In other words, what were the things going on at the Institute for which China was looking to distinguish itself as a leader, and what were those areas where the Institute needed collaborators internationally in order to continue and succeed with its research?

Wang:

I think at that time, say 20 years ago, nobody in China was talking about being a leader. We were always talking about how to catch up faster. [Chuckles] There was only one experiment that people were trying to get support from the government, which is the Beijing Electron-Positron Collider. That one was firstly started in 1984 and completed in 1988. By the time of 2020, it is pretty old. The community had been talking about upgrades for almost four or five years and didn't get anywhere, so the community at that time was struggling to get support for the upgrades. Nobody was talking about being a leader in the world. If you said that, people would look at you with a very strange eye. [Laughing]

The reason that then I went there was the possible neutrino beam from Japan to China, so I saw this as a way for China to do something distinct from the past and visible to the world. I mean, being a physicist, we always want to do something which is visible to others as a great experiment, so I thought that that was an opportunity. That’s the reason why I went there.

Zierler:

What were you looking to accomplish professionally when you got to the Institute?

Wang:

It’s very simple. I just wanted to make my own experiment a success. So, I wanted to have a reasonably big, important experiment under my leadership, and hopefully it would be successful. That was my dream at that time.

Zierler:

Yifang, in the Institute, are there opportunities to teach physics or to take on graduate students?

Wang:

The Institute has graduate students, but not everybody has to teach. So, I choose not to teach because I’m not a good teacher. I decided to do the research. In my first year, I was trying to come up with a design to detect neutrinos from J-PARC, a neutrino beam, but that quickly died because we realized that there was no hope to get the beam from Japan. I think Japan at that time was struggling with their own difficulties and troubles of funding for their own experiment, T2K. So we realized that having a beam to Beijing was too difficult, too expensive, and too complicated.

Zierler:

So, the difficulties were bureaucratic and economic. They were not scientific difficulties. In other words, in a perfect world, you could have gotten the beam from Japan and have pursued this project.

Wang:

Right, right, right. It’s purely, say, a complication of the funding, politics, and also competition with T2K, for example. People from T2K didn't want this kind of project, for example, to compete with them, so there were a lot of complications. But—

Zierler:

Now, this project in T2K, were they after the same questions or were they separate in that regard?

Wang:

Oh, the same questions. They were actually working on the same subject, theta_13 and also the CP phase of neutrino oscillation.

Zierler:

So, the politics were what exactly, that the Japanese government did not want to share the beam?

Wang:

It’s not politics in that sense. I think the politics were among the scientists because people were competing for the limited funding. People already had their own groups and their own experiments. They certainly didn't want somebody else to change their paths; they had their paths already defined. They didn't want these things being changed. Also, building a detector in China and having all this complicated…it’s also politically difficult and complicated. They had no confidence that China could do this. I think it was also a very, very reasonable concern for them, yeah.

Zierler:

Did you ever consider? Was the opportunity available for you to go to Japan and work on their project?

Wang:

I think I understood that it’s very hard for Chinese to get a permanent job there in Japan. I did work there on the KamLAND experiment as staff of Stanford, but I never tried to take a permanent job there. I think that was probably too difficult.

Zierler:

Once you realized that this project was not going to work out, what did you choose next? What was next available to you?

Wang:

At that time, the main task of the Institute of High Energy Physics was the Beijing Electron-Positron Collider. They were struggling to get the funding for the upgrade, and before they got the funding, they were working on the design. They tried to go through all the technical design report, tried to work on the R&D, organize a working group and so on. They were preparing for this upgrade, and I realized that I could join them. I actually knew the leader and the…although they had been pushing this very hard, but they certainly welcomed new, fresh blood into the project, so I decided to join them.

Zierler:

What were some of the research questions with that project?

Wang:

The science…the motivation of this project was to look for glueballs. That was actually my old interest when I was working in L3.

Zierler:

Yes!

Wang:

So, I thought this was an interesting question. The main motivation for this machine and the detector was to look for all the exotic hadrons including glueballs. Of course, they can do many, say, QCD studies, Standard Model measurements and so on, but a glueball search was one of the hot topics. So, I decided to join. They had a major issue of the detector design and also the construction, so actually my effort was mainly on the detector design and construction at that time.

Zierler:

What had changed in this research from your original interest? Were there any advances that were made, or were you essentially picking up where you left off on this?

Wang:

At that time, I had a lot of people working on this subject and they were very experienced. So, to be honest, I was interested, but I didn't really think that I was going to work on this subject forever or for all my life. I always thought this was temporary and I tried to help them to build up the detector to make the projects through and to move forward on the charm physics and so on. I didn't really have my, say, scientific dream I would like to realize in this project. I didn't have that kind of thinking at that time.

Zierler:

Yifang, another sort of national/international question. As you were getting comfortable at the Institute in Beijing, I wonder if you thought about, given your work in Europe and the United States, do you see any cultural differences that affect how physics research and collaboration is done in the three areas? In other words, is there a uniquely Chinese way of doing physics that you might only have appreciated having been elsewhere as a base of reference to compare?

Wang:

Yes, indeed. To be honest, at that time the connections of the Chinese physics community to the outside world were limited. Of course, people do have exchange of visits. They do talk to each other, but they are not really working closely on a daily basis, so the mentality is different, and the thinking is different. One of my tasks there was trying to convince people that you had to be internationalized and you had to think and to behave differently from the past. And you really had to adopt the international standard and international habits, international behavior. So, I tried to push people to be more open towards the outside world and to push them to, say, go to conferences and talk to people more frequently and invite more people to come to IHEP, and having, say, bylaws of the collaboration which are more adopted to the international standard. So, I was trying to change a little bit the Institute and to make them more internationalized.

Zierler:

Now here, Yifang, you emphasize the benefits of outside research on the Chinese perspective, but I wonder if you can flip the answer and talk a little bit about what are some of the Chinese approaches that the United States and Japan and Europe might do well to learn from?

Wang:

This is a very interesting question, and nobody has actually asked me this way. Indeed, I believe that the way the project is managed in China, I believe it’s more efficient, more effective than, say, the United States in particular. CERN, I’m not 100% sure because they have also a very successful past. But in the United States, I mean we all know some of the failures, and also, I have my own personal experience in Daya Bay we can probably talk a lot about that later on. I saw the management and bureaucracy is, to be honest, very heavy, so I didn't like that very much. [Laughter]

Zierler:

Now, Yifang, you mean the bureaucracy you saw even when you were at Stanford? You even understood the American style of bureaucracy even as a post-doc at Stanford?

Wang:

No. I have to say when I was at Stanford, of course I saw some of the bureaucracy. It was much less. It was a university group, and the project was led by Stanford and Caltech. Now when we were working on the bigger project in the United States, we all knew that it was going to be managed by national lab and Daya Bay is a DOE project. So, we saw that it is not anymore something managed by a group. It is managed by government officials. So, there you see a lot more bureaucracy and inefficiency and the complications.

Zierler:

I wonder, then, if you can explain where the Institute in Beijing fits within the government. In other words, here in the United States we would understand SLAC to be part of the national laboratory system, which is part of the Department of Energy, which is part of, of course, the federal government. You can even hear in that description all of the bureaucracy, right?

Wang:

Right.

Zierler:

So, can you explain a little bit about where the Institute fits within the larger scientific infrastructure in China?

Wang:

The Chinese scientific system is quite complicated. Of course, we have a Science ministry, which is similar to the DOE which is really government, but the Chinese Academy of Sciences is not under any ministry. It is directly under the State Council or under the Prime Minister. So, the funding comes directly from the State Council, the Prime Minister. But it’s not a government organization. It’s a research organization. It’s like universities, hospitals and so on. So, you get your funding from the government of course, but you behave as a research organization like a university or a hospital. The Chinese Academy of Sciences is just bigger, higher, I mean with more authority. Underneath the Chinese Academy of Sciences, we have something like 100 research institutions like IHEP. We are just one of the 100. We get our funding from the Chinese Academy of Sciences, part of it, and then if we need a big project like the upgrade of the BEPC, the accelerator, you have to apply to the government agency as a project. So, the Chinese Academy of Sciences helps you to apply to the government agency for this funding. Then once the money comes in, the money is through the Chinese Academy of Sciences and then to the Institute. The Chinese Academy of Sciences does have the obligation to manage the project, or at least to monitor the progress of the project.

Zierler:

Yifang, when you're applying for funding within this situation, within this infrastructure, to what extent are you free to just talk about the importance of the research for basic science, and to what extent might you feel pressured to make the case that there might be some national usefulness behind the research?

Wang:

First of all, we are certainly free to talk about what we want to do. Whether you get money or whether you get support is a different story.

Zierler:

Right.

Wang:

[Chuckles] So, we certainly try our best to get what we would like to do, and of course, government certainly tries to drive not everybody, but some of us to the “national interest,” to something more useful. You can decide to apply for the funding, and you can also decide not to apply. If you are able to survive with basic research, you go ahead. If you are not able to survive, then you are forced to apply for the funding for applications, for applied research. So, it is in the end up to you. Up to now, I think IHEP has done reasonably good to get funding for basic research. Of course, we still have to do some applied research, but I think more than 80% of our research is on basic science.

Zierler:

Yifang, I’d like to ask you about the history, the years running up to you being named Director in 2011. So, my question there was, at some point prior to that, did you feel like you were on a track toward leadership, or was this more a recognition of your scientific and administrative capabilities and it was not something that necessarily you were on the way to achieving?

Wang:

I think both. First of all, when I entered the Institute in the year of 2001, of course, nobody was thinking, who’s going to be the next director? So, I just did whatever I liked to do, and of course, when I became the leader of the detector of the Beijing Electron-Positron Collider, after a few years (I believe three years)—of course it very much depended on my performance—they named me as the Assistant Director of the Institute. So, being assistant, then you have two more steps, Associate Lab Director and then Lab Director. So, being assistant, being one of the youngest assistants, of course people know that the very natural path toward the future is, say, Associate Director and Director. Of course, there were three or four Assistant Directors. There were three or four Associate Directors, so who is going to be Director? Nobody knows, but of course, it’s one of the candidates. [Chuckles]

Zierler:

I wonder if there was ever a concern for you, Yifang, that as you moved up in administration and management that necessarily this would pull you away further and further from the research itself.

Wang:

Not really. Indeed, I try to minimize my time on the real administrative work. In many ways, my “research” is the management of the construction of the detector, management of the design of the new experiments and so on. So, of course, there’s some administrative nature in it, but this is more, say, a scientific work. It has to be someone who is really experienced on the physics and on the detector. The pure, pure administrative work I took—very little, very, very minimized. There are other directors of the divisions, the departments, and so on. All these people are actually doing 100% of the work of an administrative nature, so I rely on them.

Zierler:

Now, because you had been in the assistant position, you certainly had a good idea of what some of the responsibilities and opportunities and challenges that would happen as a result of you being director. But my question is when you're actually director, when you're actually sitting in this new position in 2011, what surprises were you facing that you might not have recognized before being named to this position?

Wang:

Not really, because I had been an Assistant Director and Associate Director for, say, eight years before being the Director. So, I saw enough.

Zierler:

No surprises.

Wang:

[Chuckling] No, no surprises.

Zierler:

Who is your boss at the Institute when you are Director? Who do you answer to?

Wang:

When I was Assistant and Associate Lab Director, my boss was Professor Hesheng Chen , and he was also a student of Sam Ting. I’ve known him well for a long time, since the L3 time, so we know each other.

Zierler:

And then when you are named Director, right, beyond the Institute, who is your boss? Who do you answer to as leader of the Institute?

Wang:

Oh, that’s the president of the Chinese Academy of Sciences.

Zierler:

I see. So, it’s a direct report to the president of the Chinese Academy of Sciences.

Wang:

Yeah. Of course, there are associate…vice presidents of the Academy, so indeed, depending on the nature of the problems, I have to talk to different, say, vice presidents or the president.

Zierler:

Is the Academy also where you apply for funding? Is it all the same?

Wang:

It’s complicated. Certainly we need to get funding from the Academy, so we have to talk to them, but also we are able to apply for funding from the Minister of Science and Technology, to the National Science Foundation, and also to a Ministry called the Commission of Development and Reform. This is a very strange name, but this ministry or commission is actually like a ministry for all the economy. So, indeed, all the money of the country came from this commission. The construction of large science projects like an accelerator came from them, so we had to talk to them. It depends on the nature of your projects, so you need to talk to different funding agencies. That’s the reason why I mentioned that before, if you are able to survive with one agency, you can just go ahead. Nobody is coming to bother you. But if you're not able to get money from any of these four, then you have to go to the industry, for example, to get money to be able to survive.

Zierler:

And that’s available to you. You have multiple avenues of funding if you need it.

Wang:

Yeah, right. It’s very much…it’s different from the US. If you get funding from DOE, you cannot apply for funding from the NSF. But here you are encouraged to get money from all the available sources.

Zierler:

Yifang, when you became Director, what were your goals? First of all, did you feel like you had a mandate? Were there specific things that you felt you needed to accomplish, even if they were not personally interesting or important to you because of other people at the Academy that you felt you needed to satisfy?

Wang:

My understanding of my mission is to make the Institute famous scientifically in the world. I think before, of course, we had this BEPC accelerator and it was running for almost 20 years. Some people know of it, but not everybody knows of it, and it’s not really very famous in the world. If you go to conferences, people list all the accelerators in the history, and very often they ignore this one. You don't even find the name on their tables or on their graph. So, of course, this means something. It means that we didn't make our result famous enough for everybody to know, and also the technology we used to build the accelerator is not something very advanced, not something that everybody wants to learn from because most likely, these are technologies other people invented. We just took it from others. So, I believe this is what had happened in the past in our institute, and it has to be changed. I was hoping that in the future, when people talk about accelerators, talk about the new particle physics projects, talk about the great results and so on, the Institute would come into their mind very naturally that they had to talk about this one, talk about this technology, talk about this result, and not just easily forget about it. [Chuckles]

Zierler:

Yifang, was it ever difficult for you to support the kinds of physics done at the Institute that you were not directly a member of yourself? In other words, were there ever any biases in terms of your own personal interests to make sure that these research endeavors did not get special treatment just because you were Director and these were the things that you were interested in?

Wang:

To my mind, no. I mean, of course, I try to treat everybody on an equal basis. Every new project is discussed in a committee at the Institute, and if everybody concludes that this is a great project we are to pursue, of course, as the Director I have to support that and I have to make sure that it is going to happen. So, up to now, to be honest, all the major projects we’ve decided to pursue, we almost succeeded in them all. We got funding. We got things moving ahead. Some are still in the process, but generally speaking, we have no major problems to get projects through. Indeed, the biggest problem we have now in our institute is my own project, the Large Circular Collider [chuckles], which we didn't really get moved forward to a very advanced level, but all the others, I think we are in really good shape.

Zierler:

On that note, Yifang, I’d like to ask you. Of course, as you well know, when the SSC in the United States failed to be completed, many people were concerned, and it’s been proven true, that the United States would sort of cede leadership on high energy physics, on collider physics, on accelerator physics. Now, the Chinese perspective, of course, is very different in that regard in that there is a very bright future in these areas in China, and so I’d like you to comment sort of broadly on what is the state of play for high energy physics in China, and where is the Institute in Beijing within that larger national endeavor?

Wang:

I think it’s a very complicated situation. In the past, we managed to get the Beijing Electron-Positron Collider through and to get the funding support. That was in the early ’80s, and still at that time, high energy physics was very well-supported. Of course, we were successful, but then we also became the victims of the success. Other scientists in the country were jealous and were criticizing that we got too much funding, and that kind of feeling continued all the way up to now. The failure of SSC, as I see it, actually had a very large negative impact to us, and other people, other scientists in the country say, “Look. The US didn't build the SSC. This is a dead field. Why do you guys want to pursue this direction?” Of course, different people have different opinions, so this is still a mixed feeling. In the end, who is going to win is not clear. But generally speaking, high-energy physics is much less supported in the community nowadays than, say, in the ’80s. In the ’80s was a golden time, and we got unanimous support, and now it becomes very complicated, partially because of SSC. If everybody in the world had a great, big accelerator, then of course it’s easy for us to argue we should also get funding for the new accelerator. But now it’s very hard. We have to…

Zierler:

But the other way of looking at it is because the SSC was never built, isn't there a prime opportunity for China to sort of assume the mantle of leadership and produce accelerators at higher energies even than what’s happening at CERN?

Wang:

Yeah. This is the one angle. This is one of the opinions, and of course there are counter-opinions. In the end, who is going to win is not clear, so we are still fighting with each other. [Laughs]

Zierler:

So, you would say, in your opinion, that this is still history that’s unfolding to this very day. These have not been resolved, these questions.

Wang:

No, no. It has not. It has not. So, smaller projects like the upgrade of, say, BPEC in the beginning of this century—it was difficult, but in the end, we succeeded in convincing the government to support us. So, in the end, we got funding to do this upgrade. But now we’ve come to the next step, and of course, that’s another new battle.

Zierler:

Where are you on these things personally in terms of the importance that you place on large-scale accelerator programs that would be designed toward really fundamental new discovery in physics? Are these areas that you think are deserving of the kind of budgetary support that is not currently feasible in the United States—$10 billion, $15 billion, $20 billion? What is your feeling on these things?

Wang:

First of all, I believe that nowadays, to build such a large project in China is more economically [feasible] than in the United States for two reasons. One, of course, is that it’s still cheaper in China—the labor and many other machining things. On the other hand, the management overhead is still much lower in China than, say, in the United States. So, I think we should take this opportunity to go ahead to build these kinds of large projects. If you wait for another 20 or 30 years, we may become very similar to the United States where we are not able to build such costly projects.

Secondly, of course, I believe that these kinds of projects are still very, very important to science and also to the technology. So, we certainly believe that if China has this kind of economic scale, then China should have enough, a fraction of contributions to science which probably in the end will be a benefit to everybody in the world. China had, in the past, say 100 years, benefitted from the civilization of the west, we didn't have the opportunity or the capabilities to contribute. But now, I think from a point of view of economic level, we are able to make contributions, so we should do that. And I believe—

Zierler:

It does raise the question, though. If there is the political appetite and there is the economic capability because the costs are lower in China, it does then beg the question—and perhaps here you can talk about some of those counter-opinions you mentioned earlier that might explain why these large-scale projects are not at a more advanced stage in a place like China, given that it seems the infrastructure is ripe for it to happen sooner than later.

Wang:

Yes…certainly there are a lot of people who believe that China is still a poor country, and as a fraction of GDP, you should not spend that much money on a pure science project like this. And on top of that, because the United States has canceled the SSC, this kind of project doesn't have a bright future even in science. So, of course, it’s hard to argue. Everybody has their own opinion. There is no absolute way to come to argue that we are right; they are wrong. It is actually back and forth, the different kinds of opinions that are flowing around in the community and sometimes also in the newspapers and the social media. There are a lot of discussions like this.

But personally, I believe that it is actually a very good opportunity for China to be a leader or to have visible contributions to the world in this particular research field. I believe that this research field is not going to die and that there is a bright future. It seems if there is a future, if you have the most advanced apparatus in your hands, you can certainly be a leader in this field in the world, so why not? I think we should do this.

Zierler:

Yifang, I’d like to ask you about some exciting news that you experienced in the not-too-recent past, and that is the major awards of the Panofsky Prize and the Breakthrough Prize. So, let’s start with the Panofsky Prize. That must have been very special to you, just because of your connection to SLAC. I’m curious. What was the research that you were recognized for that led to the Panofsky Prize?

Wang:

That was the experiment called the Daya Bay reactor neutrino experiment. We came up with this idea that…so, first of all, when we abandoned the idea to have a neutrino beam from Japan to China, we were still thinking of what we could do in neutrino physics, and then people realized that using a neutrino beam to measure θ₁₃ is too slow, and is not so accurate. People came up with the idea that reactor neutrinos should be able to measure the θ₁₃ with very high sensitivity, and indeed, since I’ve been working on this, I know all the technical details. I thought that it would be ideal for China to pursue this kind of experiment, so with my colleagues at KamLAND, Professor Kam-Biu Luk from Berkeley, we decided to collaborate on this Daya Bay experiment in the south of China. That was the beginning, yeah.

Zierler:

What about the Breakthrough Prize? The Breakthrough Prize is extremely exciting because it’s like the name suggests. It’s really recognizing fundamental contributions to really move physics on to the next level. I’m curious what your feeling was to be recognized at that level and what the research was behind that recognition.

Wang:

Yeah. So, our Daya Bay experiment was the first one to reveal the value of θ₁₃, which actually represents a new type of neutrino oscillation. So, by measuring this value, we managed to complete the picture of the neutrino oscillation. With three types of neutrinos, you need to have three types of neutrino oscillations. Super-K and SNO managed to measure the two other neutrino mixing angles, θ₂₃ and θ₁₂. Obviously, people wanted to know what the value is of θ₁₃. So, the reactor neutrino experiment is the best one for this value measurement and Daya Bay managed to be the first to reveal this value. We were recognized by the Breakthrough Prize with all the neutrino oscillation experiments, seven in total.

Zierler:

Can you talk a little bit about your work as director of JUNO?

Wang:

Yes. The Daya Bay experiment was started in the year of 2003 and completed the construction in the year of 2011, that was almost eight years. By the time of 2008— five years after the proposal of Daya Bay and three years before its completion—we were discussing what could be the next experiment after the Daya Bay experiment because we knew the Daya Bay experiment was relatively small with a single motivation—hence a very short lifetime. So, we needed to think about what we could do after that. Since we had studied this neutrino oscillation, we believed this was a very interesting topic and we should be able to continue. In the year of 2008, we came up with the idea to use reactor neutrinos again to measure the neutrino mass hierarchy and to measure the mixing angles. That is the JUNO experiment and in addition, it can measure solar neutrinos, supernova neutrinos, geoneutrinos, etc. We believed that this was going to be a very interesting experiment.

Of course, before that there were people talking about similar experiments, but that was for a different purpose—only for the supernova neutrinos and the solar neutrinos, etc. So, using this to measure reactor neutrino energy spectrum to determine the mass hierarchy was our idea and was the first one to be realized. That was the key point, and we managed to attract a lot of people in the world to work with us together for this experiment.

By the time of the completion of Daya Bay, we were asked by the Chinese Academy of Sciences, “What’s next?” We said, “Okay. We have something in our pocket for the next one. We have been prepared for almost three years, and this is the proposal.” So, we got this JUNO project approved really very quick by the Chinese Academy of Sciences. We started the construction in the year of 2015, and we plan to finish it two years from now.

Zierler:

Oh, so it’s still under construction now.

Wang:

Yes, yes, yes. This is going to be one of the three major neutrino experiments in the next decade, together with DUNE, the one in the United States, and the Hyper-K in Japan.

Zierler:

Yifang, just to bring our discussion right up to the present day, can you talk a little bit about some of the projects and research that you’ve been involved with in the past four or five years?

Wang:

My major activities were focused on both the JUNO experiment and the Circular Electron-Positron Collider in China. We call it the CEPC. So, JUNO is a very complicated, difficult detector. The Daya Bay is a detector module with a total weight of 100 tons, and we need to build a few 100-ton modules. Now JUNO is 20 kilotons, so it’s a factor of 200 larger. Technologically, it is much, much more difficult with a lot of challenges, and we have been working on this since 2008. That means we already have been working on this for almost 12 years, and I believe that we’ve managed to solve almost all the technical problems and we are about ready to start the installation. That was my main focus in the last four or five years, trying to solve all the technical problems for the JUNO detector, and then being able to construct it.

Another one is the CEPC. Right after the Higgs discovery in the year of 2012, we were discussing what the possible future of China in accelerator science is. Indeed, even a few years before, right before the completion of the BEPC upgrade, we were discussing what is next because we knew that this upgrade would not last too long, and the scientific motivation is limited.

We were discussing this for almost eight years, and finally, after the discovery of the Higgs, we realized that we could build a Higgs factory using the electron-positron collider, and this Higgs factory could also be upgraded in the future to a proton collider just like from LEP to LHC. So, the same tunnel can be used twice, for an electron machine first and a proton machine afterwards. This was actually the first in the world to have such an idea for the future of high energy physics after the discovery of Higgs. Before, people were talking about LHC and the International Linear Collider. People all thought that that was the future. So, we actually came up saying, “No, no, no. You have a different approach. The Circular Electron-Positron Collider is better, and you also have a future with the proton collider,” so that actually changed very much the perspectives of the future and the future plan of all the labs.

Zierler:

I’m curious if, in the past few years, your approach on both the collider and the neutrino projects you see primarily as Chinese endeavors, or are they part of larger international collaborations?

Wang:

They are both international projects. Of course, in the past we also participated in international projects like CMS and ATLAS and so on, but our role was not very visible. So, we would like to have, of course, international projects, to have our role be recognized by the international community, but we have to have our own ideas to initiate such kinds of large international projects.

So, JUNO is a very international project. We have more than half international members, and way more than half international institutions. We have 77 institutions now. I don't remember exactly, but I think more than 40 are the international institutions. And of course, CEPC is going to be similar. We were hoping that we’d have something like 30% international contributions to this project.

Zierler:

Well, Yifang, now that we’ve worked our way all the way to the present, I think for the last part of our discussion I’d like to ask you a few sort of general questions about your career, and then a final question thinking about the future. So, my first question is what has been accomplished in neutrino physics over the course of your career? What do you see as your own specific contributions, and what remains to be done in the field of neutrino physics as we look ahead to the future?

Wang:

Neutrino physics has been a very…the history of neutrino physics is a very interesting story. If you start in the ’60s, you see a lot of conflicting results and nobody had really a good idea how and why it looked like this. So, I remember when I was a student in the ’80s, when people were talking about neutrinos, they all smiled in a very strange way. [Laughter] But of course, there were people who insisted, and indeed, in the field there were all these, say, murky kind of results, it would be actually your opportunity, and if you were able to solve the problems, it would be a great discovery.

So, I think the Japanese actually made a very good model about it and they insisted from, say, the ’80s all the way to the ’90s. Then they managed to discover for the first time the neutrino oscillations through the atmospheric neutrinos. Then, of course, there were people working on the solar neutrinos. It’s also a great model. I mean, since the ’70s they’ve been working on this. I think these are the good examples.

Neutrino oscillation had been through also our effort. Our Daya Bay experiment managed to measure the last mixing angle, θ₁₃, and now there are only two parameters to be measured. One is the mass hierarchy and the other one is the CP phase. So, these two parameters are going to be measured or determined by the future three experiments: JUNO, DUNE, and Hyper-K. So, I believe that ten years from now, the neutrino oscillation issue is going to be closed. Of course, people can still improve the precision, but the question itself is more or less known.

The next big problem is the neutrino mass, the absolute mass. The oscillation only tells you the relative mass, the mass difference, so I believe that the next 20 years from now we are going to see major achievements on the neutrino absolute mass through neutrinoless double beta decays. Right now people have been working on the neutrinoless double beta decays based on a target of something like hundreds of kilograms. In the future, if you are able to increase the target mass to something like tens of tons or even hundreds of tons, you should be able to measure the neutrino absolute mass to a sensitivity or level of 1 milli-eV. At that kind of sensitivity, you can measure the mass of neutrinos with a finite value, so the problem of absolute neutrino mass will be solved. I think, 20 years from now using, say, 10 tons or even higher target mass for double beta decay neutrino experiments.

The further after we should look for the nature of neutrinos, whether it’s Dirac or it’s Majorana. So, neutrinoless double beta decays serve both purposes. Even if you don't see the neutrinoless double beta decays, you can still measure the neutrino absolute mass, and if you are lucky and you see also the neutrinoless double beta decay events, then you can tell also the nature of neutrinos. So, I believe that this is really the future of neutrinos. For this purpose, we are working on the JUNO detector to have a future upgrade. Indeed, the JUNO detector can be upgraded, say, ten years from now for double beta decay searches and maybe in 2040 we should be able to see either a neutrino double beta decay event itself or we can measure the absolute neutrino mass. That’s my vision for the future. [Chuckles]

Zierler:

Very exciting indeed. Yifang, now on to the high energy physics, the accelerator physics, the collider projects. I’d like to ask, over the course of your career, both in terms of your institutional affiliations and your own research, what do you see as some of the major advances that have taken place in these fields? Again, looking to the future, in what ways is the Institute situated to continue its trajectory of leadership in this area and very exciting pursuit of new physics?

Wang:

First of all, up to the completion of the discovery of all the elementary particles predicted by the Standard Model, we are actually at the turning point. We have to look for the next path. The best way to find the next path is through Higgs. Higgs is the strangest particle, the least-known particle, and it is actually coupled to strange words like dark matter, like the future of the vacuum, the possible future, new nature of space and time. So, we believe that Higgs is really the window towards the future, and we should build a Higgs factory to study its properties to find out deviations from the Standard Model and then through there, we go to the future. So, starting from the Higgs factory to measure all the couplings, find out the deviation. Then if we have the deviation, we can go ahead and build a proton collider to directly reveal the real particles or the real evidence. I think that’s the way towards the future.

In this sense, I think we can play a visible role. In the past, say in the last 30 years, we did have some contributions, but really did not play a key role. We always followed everybody else’s decision or whatever desire to move forward. This time, we would like to behave slightly differently, so we did tell people that we should go this direction, circular Higgs factory, followed by a possible pp collider. That was our contribution. Then, of course, since we pointed out—this is the future direction, we have to do it. [Chuckles] We should not just have people to do it and we stay behind, so we have been working on the design of the Higgs factory and fortunately, this is our expertise. We have been working on the lower energy e⁺e^- circular collider for 30 years, so a higher energy e⁺e^- circular Higgs factory, circular collider is actually not a terribly, terribly difficult thing for us. We try to work on the technology, design and so on, and hopefully it can be realized.

In addition, we are working on the possible future proton collider because, first of all, we have to make sure that the tunnel we build for electron machines is going to fit the future proton machines. We don't want to regret after 20 years that this is a wrong shaped tunnel, and the proton machine cannot be housed there. That would be a shame. So, of course, we have to make sure that the tunnel itself fits both the electron machine and the proton machine.

Secondly, we should look at new technologies. The reason in the past that a proton machine like SSC failed is because technology is not advanced enough. A superconducting magnet is too expensive, and the contributions to society by industry were not large enough. That’s why the government was hesitating to support it. Now, if we want to convince the government to give us money for the proton collider, we have to give them something back. I think the easiest way or simplest thing for us to give back to them is the superconducting technology, so we should come up with new technologies for the superconducting magnet—that is, the high critical temperature superconducting materials.

So, we have been working with other research institutions in China and also with companies to try to improve the properties of ion-based superconducting materials so that in the future, ion-based cables can be used for the future magnets because ion-based superconducting materials intrinsically are cheaper, easier, and good from the point of view of performance. So, if we are able to make it useful, usable for the future, then it’s our contribution to the society, and if we’re able to do that, we should be able to get money for the proton machine. So, that’s what we are trying to do nowadays, and we don't know how much time it will take, but that’s our effort right now.

Zierler:

Yifang, I wonder if you can reflect, both in your capacity as a research physicist, but also in your capacity as an administrative leader in science. In what ways have advances in both collider projects and neutrino physics helped each other, both in terms of the science and in terms of the funding to continue on with both projects?

Wang:

It is probably not very general, but in the specific case for myself, when I was the leader of BPEC, I was working on the detector, and when I decided to work on the neutrinos, I had the team working on the detector. They knew the same technologies of detectors, so they can actually move to neutrinos. Indeed, I managed to know each other, and I am able to shuffle people from the two projects back and forth, depending on the schedule, depending on the specific needs, and so on. Indeed, this is a way to best use the limited manpower. So, if I’m not in that kind of position and if I have to have two independent teams working on the Daya Bay neutrino detector and the BESIII detector, then I think for whatever is available at that time, we would not be able to complete the job.

So, the same happens also again now. Because of the success of Daya Bay, we managed to have the JUNO project, and in the future, I believe if we have the success with the JUNO experiment, it’s going to help us to get the circular collider project because you demonstrate your capability. If you demonstrate you are able to get very difficult things done and you have great scientific results, you get the credibility in the community, so you should be able to get the funding for the next project. Of course, from the point of view of manpower, you can shuffle people back and forth into different projects, which also helps you to solve the problem of the manpower.

Zierler:

Yifang, I’d like to go back to a very interesting thing you said about the value of scientific competition in order to secure funding and support from your home government. I’d like to broaden that question out and ask you about what role do you think scientists have in managing the competition between the United States and China generally in the 21st century? In other words, who knows what the future may hold, but there is likely a strong chance that scientific collaboration between our two countries will serve positively and productively to keep the US-China competition peaceful and productive and mutually beneficial, and not the negative consequence that may come as a result of international competition. So, I wonder if you can reflect broadly on where you see the origins of US scientific competition and collaboration and how the scientific communities of both countries might play a productive role as we look in the decades ahead.

Wang:

That’s a very difficult question. Of course, we can only try our best. From my point of view, I believe that scientific research represents the interest of all the people in the world. Everybody has that interest. So, if we have a common interest and if we are able to benefit from everybody’s interest—namely, collaboration—then I think the collaboration will happen.

In the past, CERN was a model to make Europe more peaceful than before. Of course, it was not the only reason, but it certainly helped a lot to [develop] trust between different people who were enemies in the past. Even during the Cold War, the Soviet Union, the United States, and the Europeans could collaborate on science, in particular at CERN. So, I believe that a large international science center in the US, in China, in Europe will help all of us. If it’s only in the United States, maybe the government decides not to have the Chinese work in their science center. Then that collaboration cannot happen. If only in China, it could also happen that way. So, if we have science centers everywhere and if they are, say, mutually beneficial to everybody, the collaboration will happen. In particular, basic science is not so sensitive, so people should easily accept this kind of collaboration, even in a very difficult political atmosphere.

So, I think scientists indeed could play a very important role, and we really hope that all scientists in the world can unite together and collaborate in a broad way, but of course, on the project itself level, we could have competition and that’s the way to make us excellent. Without competition we cannot be excellent. But we certainly have to collaborate on a broader scale.

Zierler:

Well, for everybody’s collective benefit, that’s a very wise approach, and I certainly hope it plays out just as you suggest it should.

Wang:

Thank you. Yeah. I hope it can happen. [Laughs]

Zierler:

Yifang, for my last question, I want to ask you what’s left for you personally? What are the areas in physics that you are so excited about in the future, both in terms of your own research as a scientist and in your capacity as a scientific leader to direct the next generation of young physicists as they look well into the 21st century and what might be possible for them?

Wang:

Yeah. So, my personal interest now is to complete the JUNO experiment. Certainly, this is my primary scientific interest so that for the next five…up to ten years I will continue to work on the neutrino experiment. For the CEPC, I think that’s really very far away, and that’s my contribution to the next generation. I hope that I can pave the way for them so that they have a new machine for themselves. I should try my best, but [laughs] it’s hard to know.

Zierler:

Well, Yifang, it’s been an absolute pleasure speaking with you today. I’m so glad that we connected through our mutual friend Sam Ting. It’s been very special to hear your perspective because I usually only hear the American perspective on physics, so this is very important to our collection and to what we’re trying to do because it does emphasize that physics and science is a collaborative and an international endeavor, and we’re better for working together than not working together. So, I’m deeply appreciative of our time together, and I wish you much success in your future.

Wang:

Thank you. Thank you very much.