R. J. Holt

Notice: We are in the process of migrating Oral History Interview metadata to this new version of our website.

During this migration, the following fields associated with interviews may be incomplete: Institutions, Additional Persons, and Subjects. Our Browse Subjects feature is also affected by this migration.

We encourage researchers to utilize the full-text search on this page to navigate our oral histories or to use our catalog to locate oral history interviews by keyword.

Please contact [email protected] with any feedback.

ORAL HISTORIES
Image not available
Interviewed by
Catherine Westfall
Interview date
Location
Argonne National Laboratory
Disclaimer text

This transcript may not be quoted, reproduced or redistributed in whole or in part by any means except with the written permission of the American Institute of Physics.

This transcript is based on a tape-recorded interview deposited at the Center for History of Physics of the American Institute of Physics. The AIP's interviews have generally been transcribed from tape, edited by the interviewer for clarity, and then further edited by the interviewee. If this interview is important to you, you should consult earlier versions of the transcript or listen to the original tape. For many interviews, the AIP retains substantial files with further information about the interviewee and the interview itself. Please contact us for information about accessing these materials.

Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event. Disclaimer: This transcript was scanned from a typescript, introducing occasional spelling errors. The original typescript is available.

In footnotes or endnotes please cite AIP interviews like this:

Interview of R. J. Holt by Catherine Westfall on 2013 July 16,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/38254

For multiple citations, "AIP" is the preferred abbreviation for the location.

In this interview R. J. Holt discusses topics such as: his graduate education at Yale University; Continuous Electron Beam Acclerator Facility (CEBAF)/Jefferson Laboratory; Don Geesaman; particle physics; HERMES experiment; University of Illinois and Urbana-Champaign; spectrometers; Stanford Linear Accelerator Center (SLAC).

Transcript

Westfall:

This is Catherine Westfall. It is the 16th of July, 2013, and we’re at Argonne. I’d like you to start a little bit about your own history and where you got your PhD. Did you do your PhD on electron scattering work?

Holt:

Yes. I got my PhD from Yale in ‘72. I became interested at Yale in electron scattering and photonuclear physics. My advisor was Frank Firk at Yale. He was interested in photonuclear physics, and at that time, because of funding pressures just when I was coming into the lab, as you might remember in the very early ‘70s, there were large budget cuts in the field. The electron accelerator could no longer run high duty factor, and so the electron scattering program was brought to a halt. So I became interested at that time in photonuclear physics and actually wound up doing a Ph.D. thesis on neutron scattering. [Chuckles] Since there were no jobs in 1972, I stayed on as a post-doc at Yale for another couple of years.

Westfall:

You might be interested to know that sort of between 1968 through the early ‘70s, a colleague of mine estimates that almost an entire generation of physicists was lost…

Holt:

Really?

Westfall:

…because of the funding drought.

Holt:

Budget cuts? Yes. That’s interesting.

Westfall:

But you survived. [Laughter]

Holt:

[Laughing] Well, barely. At that time I had the idea to try to photodisintegratethe deuteron, measuring the photoneutron polarization. Actually my advisor stimulated that idea. But I wanted to build a liquid deuterium target to get really good results instead of using heavy water or deuterated polyethylene. So I proceeded to design and build the first liquid deuterium target, based on closed-cycle refrigeration, used in the country, I believe, and we did the experiment. Then I performed a couple more polarized neutron scattering experiments at Yale and then came to Argonne in ‘74 as an assistant scientist and worked with Harold Jackson in the low energy photonuclear facility that he built here. To that facility I brought polarization expertise. For a number of years, I performed low energy photonuclear, photoneutron experiments. But I had this overall philosophy that I probably learned from my advisor, of using an electromagnetic probe, something we really believe we understand, on the simplest nucleus and see if we can make sure we get that right before going to more complex nuclei. That was sort of a guiding philosophy in my whole career, actually. Well, in ‘76, there was this report from the Livingston panel that said there should be a big electron accelerator. I’m not even sure I heard of it in ‘76, but probably by ‘77 or so I had. When Harold Jackson came back from Saclay — he was on a sabbatical in Saclay about the year after I came to Argonne — he set up a working group here with two accelerator physicists and me initially. I think that was about ‘78.

Westfall:

Mm-hmm [yes]. That’s interesting. Okay.

Holt:

And we started studying electron accelerator designs. We even put forward a report in ‘79 comparing the three designs, you know, the double-sided recyclotron, the linac ring design, and the microtron design. So with these two accelerator physicists, we did the study of those three options, the advantages and disadvantages. The double-sided recyclotron, the present JLab design, we rejected first. The reason was that there were no reliable superconducting RF cavities at the time, and you couldn’t afford the electricity to run this design with room temperature cavities.

Westfall:

I imagine that the HEPL problems figured into your calculations.

Holt:

Yes, and we were watching the Urbana people struggle with the HEPL cavities. So then we went to a linac-ring design, and we identified two weaknesses in that. One was the linac, and the other is the ring (that’s a joke). The other problem is the extraction of the beam from the ring. We didn’t think, because of limitations on the linac and the extraction, that you would really get the design goal. As far as I know, no one ever has achieved a really high current from a linac-ring accelerator.

Westfall:

Just out of curiosity, was Jean Mougey already at Saclay at that time?

Holt:

Yes. Oh, he was a big influence on me personally.

Westfall:

Interesting.

Holt:

I had read his (e,e’p) papers. I had seen the beautiful work that he’d done just unraveling nuclear structure.

Westfall:

Excellent. Okay.

Holt:

Saclay was running circles around us. We had LAMPF at the time. We were trying to do pion scattering. I followed the same approach at LAMPF that I did here. So Jean Mougey had been doing beautiful work. Saclay was doing beautiful work: Bernard Frois and others. So we had been working at LAMPF trying to do pion scattering from nuclei, and I tried pion-deuteron scattering… actually, partly under Tony Thomas’ influence, who was a young theorist at that time at TRIUMF. He later became a chief scientist at JLab, but he was at TRIUMF at that time. We built a polarimeter and measured the tensor polarization in pion-deuteron scattering. I’ll kind of say why that’s interesting maybe later if you have time. Anyway, I sort of concluded early on that Saclay was running circles around us, intellectually in terms of actually getting at what we would like to measure about nuclei. We had Bates. We had MIT Bates, but it didn’t run very well at the time. So I thought we were at a big disadvantage relative to Europe in nuclear physics. This was my feeling at the time.

So next we figured out that there probably were a couple of accelerator options. We looked at the double-sided microtron because the Livingston panel recommended a 2 GeV machine. A single-sided microtron wouldn’t do it, so we looked at the double-sided option. And we looked at the linac ring, and those looked like two options that probably could be carried forward. We carried them forward until we discovered the weakness with the linac ring design. The next task was to put together the science case. I focused on electron-deuteron elastic scattering. I should say that indeed… Well, we were beginning to suspect there could be quark effects in the nucleus. One is the EMC effect.

Westfall:

Can you pin that down, when you began to suspect?

Holt:

Well, there were — No. Actually, EMC came a little later.

Westfall:

It did.

Holt:

Yes. That came later, but initially came the scaling, and I think that was showing up in the late ‘70s.

Westfall:

Lepage/Brodsky, right.

Holt:

Yes. They had been seeing some scaling — they called it precocious scaling — in electron-deuteron elastic scattering, and that made us suspect that if we just went to a little more momentum transfer, it would be very clear. So I was very interested in electron-deuteron scattering. There are actually three form factors since it’s a spin-1 object. A spin-0 object has one form factor, and a spin-½ like a nucleon has two, and the deuteron has three form factors (charge, quadrupole, and the magnetic form factor). If you just do unpolarized scattering, you can only isolate one of those form factors, the magnetic. The charge and quadrupole form factors had never been unraveled. So you need one more measurement to do that, and we chose t20 in electron-deuteron scattering. We had already been measuring t20 in pion-deuteron scattering, so we emphasized measuring that at extremely high momentum transfer, and this should tell the story. Carl Carlson and Franz Gross had a prediction that t20 would go to a certain value when perturbative QCD set in. It would go to — square root of 2. —

Westfall:

I believe that Don said that he was wrong.

Holt:

Brodsky was wrong?

Westfall:

Right.

Holt:

Well, he’s not in some aspects of the problem — [Laughs] Well, it’s a funny thing. I mean perturbative QCD, what can you say? I mean there was a tension building at that time between perturbative QCD and pion exchange theory, the Yukawan picture of nuclear physics.

Westfall:

Yes, the Yukawan picture was older, right?

Holt:

Yes. The problem we were having — actually I think Carl Carlson said it best. Let’s see. I forgot exactly. Let me paraphrase. Meson exchange theory is always right, but it never works. Perturbative QCD is always wrong, but it always works. [Laughter] So that was an amusing observation.

Westfall:

Explain a little bit more what that means. So the older classical meson-meson exchange theory always works?

Holt:

Well, it always… No, it’s always right.

Westfall:

It’s always right.

Holt:

You know, we always believe in it. We always believe in meson exchange theory, and we always believe that there’s pion exchange going on between nucleons.

Westfall:

But then when you look at the data…

Holt:

When you look at the data, it disagrees, especially as you go to higher energies.

Westfall:

So what you’re really looking at — The problem, I’m guessing, that you’re saying is that you go up to high enough energies and QCD works. [Yes.] You go to low enough energy, and the meson-meson classical theories work.

Holt:

Yes. Exactly.

Westfall:

But it’s in this in between period —

Holt:

Yes, the transition.

Westfall:

The transition period.

Holt:

And that’s the region I became interested in. How do we make this transition from meson nucleon degrees of freedom to quark gluon degrees of freedom? We know at very high energy, perturbative QCD undoubtedly works. I mean high energy physicists have shown actually that it works, and we’ve shown at very low energies our meson exchange model works pretty well. But there is this transition region that we thought we could explore.

Westfall:

Well, the way that Larry Cardman put it is that it’s during this period that he began to understand that to really understand nuclear structure, you had to understand the quark-like structure of nucleons in nuclei.

Holt:

Yes, we started believing that. I think we were buying into that general idea, but there were some experiments that came along later (like the first EMC effect and the second EMC effect in ‘88) that really drove us. I mean that drove us over the cliff. [Laughter]

Westfall:

I thought that Don Geesaman spoke of a spin EMC paper in ‘86. Is that the one you’re referring to?

Holt:

I think it was ‘88. It could have been ‘87.

Westfall:

That would make sense because when I tried to find it in ‘86, I couldn’t find it. Okay. But that’s the one you’re talking about that’s the spin?

Holt:

Right. It’s the spin crisis paper. Sometimes people call it the second EMC effect because CERN also discovered it. So that really drove our thinking into the direction of quarks, you know, those two experiments…

Westfall:

Right. The interesting thing about that is that that is actually after the ‘86 CEBAF design report…

Holt:

That’s right.

Westfall:

…which means that the people who were building the equipment and wanting to recruit people had the advantage of this growing interest in looking at this transition range.

Holt:

Yes. That’s right. I think Brodsky put the fix in back in the Barnes report in 1982. [Laughter]

Westfall:

Right.

Holt:

By boosting the energy from 2 GeV to 4 GeV.

Westfall:

And just to be clear, you remember already having the idea when you did the GEM report that… I think by the time of the GEM and SURA proposals in the early 1980s, it’s already clear that you want to look at this transition range.

Holt:

That’s right. And I thought the best way to see it was in the deuteron because there was a definite prediction from Carlson and Gross for pQCD that t20 would go to -√2 when you hit this region, whereas the meson exchange model had it going positive. It was just a totally opposite prediction, and I thought, “That’s clear. So let’s go measure that.” So that was already, I think, being discussed in the Blue Book. I wrote a paper in the Blue Book.

Holt:

I made a contribution to the Blue Book on t20 and e-d scattering.

Westfall:

What I have from the Blue Book is the table of contents, so that might be helpful, I think.

Holt:

Yes, maybe that… Let’s see. Oh, here it is. Yes, “Tensor polarization in electron-deuteron elastic scattering.” Page 169.

Westfall:

Page 169 of the Blue Book.

Holt:

Yes, yes. I was promoting that experiment.

Westfall:

Just to be clear, that experiment was based on the idea that…

Holt:

Yes. Well, I had two reasons for doing it. One is to isolate the charge and quadrupole form factors for the first time, and that way you could really get a good test of the theoretical descriptions at the lower momentum transfer and then drive the experiment to high momentum transfer and see if there’s any trend toward this pQCD limit. So I think there were two important reasons for doing this experiment at the time. Besides the reasons I’ve already given you, one of the reasons I started working on the big electron accelerator project was that it was basically boosting the energy and current over what we were used to by a factor of ten. It was boosting the duty factor over what we were used to by at least a factor of 100, and we could talk about spectrometers that had ten times the solid angle of the SLAC spectrometers. So with all these improvements, our dream was to have a facility with three independent beam lines that were independent in energy and current, and that’s where a machine like the microtron or the double-sided recyclotron excelled. The linac ring could give you three beams, but they would all be the same energy. So that was, I thought, another problem for the linac-ring design. So our dream was to boost our capability in all these parameters, and that’s what brought me into work every day and kept me late at night and weekends, is trying to figure out how all this could be done. Hal put me in charge of the experimental area design and cost.

Westfall:

Now the four parameters, just to make sure I understand, the four parameters were…

Holt:

Beam current, beam energy, duty factor, and large solid angle spectrometers where you could really make tremendous gains in figure of merit over previous experiments. So we set up a design team here with Don Geesaman and Ben Zeidman to design the experimental equipment, and Hal handled the accelerator group in making our design for the double-sided microtron. Well, when it went from 2 GeV to 4 GeV, the design went to a three-sided microtron. We had very talented accelerator physicists at the time. They were brilliant. They actually figured out the scheme for extracting three independent beam energies and currents. Either that was well-known in the field of accelerator physics, or JLab adopted that idea from our proposal and made it a reality. I worked on beam lines, the experimental halls, the photon tagging business. Our vision was three halls. One hall had two moderate resolution spectrometers. One spectrometer went to the full energy of the beam, and one went to half. The second hall had a photon tagger and a couple of moderate resolution spectrometers, and a third hall had two high resolution spectrometers. I think that’s more or less been realized at JLab. That was in our proposal.

Westfall:

Now an interesting thing was when I looked as a non-specialist at the GEM proposal compared with what I knew was built at JLab, it looked like you didn’t have a 4π —

Holt:

That we didn’t have. That we didn’t have, and there were two reasons for that. One was simply cost. You know, we were living under the cost limit of about $100 M at the time. I don’t think any of the original proposals had that, but I don’t remember full well. Certainly in those dollars, a detector like that would have been at least $25 or $30 million dollars. Today it would likely cost about $60 M.

Westfall:

So you wanted a large solid angle spectrometer…

Holt:

Yes, large solid angle.

Westfall:

…but not a 4π solid angle detector.

Holt:

Yes, right. So to keep costs down, we just stuffed a couple more medium resolution spectrometers in the photon tagging hall, and the CEBAF scientists had the brilliance to put in a 4π detector. I thought that was really a unique facility.

Westfall:

You mean JLab did.

Holt:

Yes, JLab. Probably Bernhard Mecking.

Westfall:

That is what Don guessed. He says that you really got the Hall A equipment thanks to Jean Mougey coming.

Holt:

Yes, yes.

Westfall:

And the Saclay-like Hall A equipment thanks to Jean.

Holt:

Exactly.

Westfall:

And that you got this 4π detector thanks to Bernhard, who came from Bonn.

Holt:

Yes. Right. Some of us also were not convinced you could get the luminosities in that detector technically.

Westfall:

In JLab’s CLAS detector.

Holt:

Yes, the 4π detector. I was one of those. At the time, they were talking about 1033 luminosity, which I thought was okay. It’s a little low, but I didn’t know if they could even achieve that. But they did, actually through some very clever designs and getting rid of Moeller electrons and other effects that limit 4π detectors. You’ll have to remember that at that time, the 4π detector at the PEP ring at SLAC was only handling 1028 luminosity. 1029 would have been pushing it. If you look at the HERA detectors, they basically can handle 1031 luminosity. So having a detector that handles 1033 was pretty amazing, and of course today it handles 1034, and they’re heading in the new design for 1035.

Westfall:

Okay. Well, one thing that you haven’t mentioned of course that happens by the time that you’re running and taking data with CLAS is that the accelerator was switched to an SRF accelerator.

Holt:

Sure. Yes.

Westfall:

So originally when you were competing with the SURA proposal, you were —

Holt:

Yes. Well, we didn’t hear about the breakthrough at Cornell on superconducting cavities until about ‘84. That was a year after the electron accelerator “shootout” in Washington, D.C. If we had known about the superconducting cavity breakthrough, I believe that our first choice would have been a double-sided recylotron. [Laughs] It would have been expensive and possibly rejected at that time based on cost, but I think it would have been worth it.

Westfall:

Were you one of the ones, by the way, that Hermann Grunder talked to when he accepted the directorship in the mid ‘80s and talked to people and discovered that people were saying because of the advances at Cornell, you really should switch it to an SRF accelerator.

Holt:

I wasn’t one that he talked to at that time about that.

Westfall:

But you were like-minded with the people.

Holt:

I was like-minded, yes. [Laughter] A little known fact is that when they had the linac ring design and when it won the competition, I had already been thinking about internal targets. We had run a t20 experiment at Bates in e-d scattering in ‘82, and it was such a beastly difficult experiment. I looked at the idea of putting a tensor polarized deuterium gas target in an electron storage ring because then you could get the energy and duty factor already. We already had electron storage rings. I had been looking at the Aladdin Ring in Wisconsin. It was a 900 MeV electron storage ring with 100 milliamps of circulating current. Of course it wasn’t working yet, and it took years for them to get it to work. But we did a test in that ring and showed that you could put an internal target in it and not disturb their beam.

So I started off in that direction, and I gave a talk at the 1983 CEBAF summer workshop in Williamsburg on using an internal polarized target in the Aladdin Ring. I thought well, this would fit in nicely with their plans. Now that CEBAF planned to, have a linac ring, you could always store the beam and have an internal target. After this talk, Roy Whitney at CEBAF called me and asked me to chair and organize an internal target working group for CEBAF. For a couple of years, there was a CEBAF Internal Target Working Group, from about ‘83 to ‘85. We would have regular meetings every several months probably. We met in the VARC building.

Westfall:

Yeah. Just for the tape, I don’t remember if I said this for the tape recorder. But he just said CEBAF. That’s Continuous Electron…

Holt:

Beam Accelerator Facility.

Westfall:

Thank you. I couldn’t remember. Which was the earlier name of JLab, or Jefferson Lab. So continue. So you were working on this, and then they switched to an SRF that couldn’t use this!

Holt:

No, we couldn’t do it. At that time, we’d been meeting. We had met with the Caltech group and the MIT group. We were meeting at CEBAF at the time and were having these meetings discussing all this exciting physics we could do with internal polarized targets. Richard Milner and Bob McKeown got the idea to use an internal polarized helium-3 target, and Stan Kowalski at MIT was thinking about building a linac ring at MIT. Then by ‘85, they changed the design. I think it was ‘85. [Yes.] Something like that. So this group disbanded, clearly. I remember that Stan Kowalski called me and asked whether he should pursue a linac-ring at Bates. I told him “Look, you’ve got a free field now. If you want to build a linac ring, there isn’t going to be another one in the U.S.”

Westfall:

At MIT.

Holt:

Yes. “You could build your ring now without any competition from JLab,” and that’s what they did. Milner went on to the PEP ring at SLAC, and Burton Richter, who was the director of SLAC, said, “There will be no polarized beam in this ring.” So at that time, the European high energy physics community were discussing building HERA.

Westfall:

At where? At SLAC?

Holt:

At Hamburg, DESY.

Westfall:

Oh, at Hamburg. On DESY.

Holt:

Right, DESY Hamburg. Eventually, Milner went on to propose the HERMES experiment at DESY, which is an internal polarized target in the HERA electron storage ring. That was driven by the second EMC effect in ‘88. We had a meeting at Caltech in ‘88 with Prof. Dr. V. Soergel, who was the director general of DESY. Soergel gave a stimulating colloquium at Caltech on the plans for HERA. He encouraged us to put in a proposal for the HERMES experiment and do deep inelastic scattering on polarized targets to try to understand the spin crisis. Polarized helium-3 is a good way to get a polarized neutron. That was the idea.

Westfall:

Well, what I’m curious about as I’m listening to this is…So how did you get drawn back, or when did you get drawn back? How and when did you get drawn back to JLab?

Holt:

Ah yes. Well, I had gone on to Novosibirsk. I formed a collaboration with Novosibirsk in ‘87 to put a tensor polarized deuterium target in the VEPP-3 ring, and in ‘88 we began performing experiments there. We delivered our first target cell to Novosibirsk in ‘88. That was going along nicely, and the spin crisis emerged in ‘88. It was a big year. At that time there had been PAC meetings at JLab, but they were only for non-binding Letters of Intent (LOIs).

Westfall:

The first two PACs were that way, right.

Holt:

I basically thought that it was a waste of time. Nevertheless, in 1988 I did put in a letter of intent to CEBAF for a high energy deuteron photodisintegration experiment (CEBAF LOI 88-24).

Westfall:

It really was a route to MOUs, memorandums of understanding, to help get people to build the equipment.

Holt:

Yes. So what happened, there was a parallel track. I think largely because of the EMC effect, Don Geesaman went on to FNAL, to help build and eventually lead the E665 experiment at Fermilab. At the same time, the Nuclear Physics at SLAC program, NPAS, was underway.

Westfall:

Right. I was going to say that. Right.

Holt:

I think it was starting in ‘84. NPAS, Nuclear Physics at SLAC. I was invited to be on their PAC, I think, in ‘84, and they may have had the first PAC meeting in ‘85. I’m not super sure of the dates right now. We had seen Brodsky and Hiller’s paper in ‘83 come out in Phys Rev C. Here were high energy physicists publishing in Phys Rev C, and I was startled to see this paper.

Westfall:

Right. Whereas high energy physicists would usually publish in Phys Rev which?

Holt:

D.

Westfall:

D, as in dog.

Holt:

So I ran across their paper and I read it, and I said, “Hey, look. With photo-disintegration of the deuteron at high energy, you can test this scaling idea and precocious scaling.” They had a very interesting article, and I read it. Then I was invited to be on the PAC at SLAC. At the time I said, “Well, I don’t know what that means,” because none of us knew what was going on at SLAC really. There was a general feeling that DOE would like to put a little money at SLAC for nuclear physicists so they could start training people to use CEBAF, a multi-GeV accelerator. Basically I don’t know why NPAS exactly was approved, but that could have been part of the reason. Ray Arnold was a big promoter of the Nuclear Physics at SLAC program.

So I started looking at the equipment available in End Station A at SLAC, and I saw these two spectrometers and I realized, “Well, we can do this Brodsky-Hiller experiment at SLAC.” So I put in a proposal, but now I’m on the PAC! [Laughter] I didn’t exactly know how to handle this,so I called Dick Taylor, who had invited me to be on the PAC.

Westfall:

Now this is the Taylor of Taylor, Kendall, and Friedman

Holt:

Yes.

Westfall

Yes, that did the Nobel Prize winning experiment in ‘69, I think, that won the Nobel Prize much later.

Holt:

Yes, right. 1990.

Westfall:

That showed the point-like nature of quarks.

Holt:

Yes, yes. So he basically encouraged me to go ahead and submit the proposal. Later in some PAC meeting, Taylor defended me by saying, “Any PAC member with an IQ of more than two digits will become interested in this program and submit a proposal.” I think that insulted some of our PAC members! [Laughter] But he was good at that.

So anyway, of course I had to sit outside the room during PAC deliberations. The way I proposed this experiment — NE2 was the number of the experiment — was that I wanted a very clean Bremsstrahlung beam, and I wanted to dump the electrons in the hall. Dick Taylor didn’t like that at all, so it didn’t get approved. So we came back the next year, which was probably ‘86, with experiment NE8, and that just took the electron beam straight through the target. You put an upstream radiator in and out of the beam to measure the Bremsstrahlung difference. So he liked that better, but we were beat out… SLAC had the rule that they only approve one experiment at a time. So the lab focuses resources on one experiment at a time, and then they have a PAC to decide what the next experiment will be. So only one experiment gets approved, and our experiment didn’t get approved. Then we brought it back a third time, I think in ‘87, and it was approved. Then we ran it, and by ‘88, we realized that we’re seeing the scaling that Brodsky is talking about above 1 GeV (deuteron photodisintegration above 1 GeV). That experiment went to 1.6 GeV, and that was very exciting. So ‘89 rolled around, and now CEBAF said, “We’re going to have real proposals. They’re going to be rated. They’re going to be assigned beam time.” I said, “Okay, we’ve got to do this!” [Laughs] So I put in a proposal. I think our entire group realized that was a big event, and I think we put in four proposals.

Westfall:

And then in the meantime, the spin crisis happens in ‘88. [Right.] So does that further with your desire to do this kind of physics?

Holt:

Well, I think not…

Westfall:

Directly.

Holt:

Not directly. It whetted our desire to do HERMES and to join Milner and his colleagues at HERMES to try to understand that. There were several physics reasons why I thought that we should join HERMES instead of the SLAC versions of that experiment or the EMC version of that experiment. I believe that the physics productivity from HERMES has confirmed our choice.

Westfall:

Which was at CERN.

Holt:

EMC was at CERN, HERMES was at DESY. So there were three options on the table in about ‘89 or ‘90 — ‘90 for sure — and we decided to join HERMES. That could be a long story in itself of why I was pushing for that. But basically, in ‘89, we started putting forward JLab proposals in earnest, and I think we put forward about four proposals that year from Argonne. One was to extend the deuteron photodisintegration up to 4 GeV, whereas at SLAC we had it measured up to 1.6 GeV, and it was just turning over and looking like scaling. The question was would it continue to follow the scaling law or is it going to go some other way? So that was very exciting for me and drew me back to JLab.

Westfall:

Okay.

Holt:

Yes, there was another event, by the way, which drew us back, and that was the ‘89 O’Hare meeting that Grunder set up with Eisenstein at UIUC and Hal Jackson here at Argonne.

Westfall:

So Eisenstein, and his first name is…?

Holt:

Bob.

Westfall:

Bob. And he’s at which institution?

Holt:

He was at UIUC. It was University of Illinois at Urbana-Champaign.

Westfall:

Okay, so he was at Urbana.

Holt:

There were two Bob Eisensteins at Urbana, by the way, in the Physics Department at that time, so you should get the right one. [Laughs] It confused me for a long time.

Westfall:

Okay. That’s not fair.

Holt:

Right! [Laughter] There was one in high energy physics and one in nuclear. The one in nuclear —

Westfall:

I think the Eisenstein that was on the PAC was the right Eisenstein, I think.

Holt:

Right. That’s right.

Westfall:

The correct Eisenstein.

Holt:

Yes, and he also went to the NSF.

Westfall:

Okay, correct. So that’s the only one I’ve had anything to do with, but it’s nice to know that…

Holt:

There’s another one! [Laughter]

Westfall:

Larry Cardman wanted me to ask you a question. So it was his impression that Hermann Grunder was very determined, wanted to facilitate getting more participation from the University of Illinois and from Argonne, which in Hermann’s opinion had been less because of lingering irritation at the loss of the design. So he formed this series of meetings, and the one that Larry in particular remembers is the one at O’Hare. But Don remembers, he said, that there were a series of meetings. So my question to you —

Holt:

Well, that sparked a series of meetings. That O’Hare meeting sparked a series of meetings.

Westfall:

But in particular what I’m wanting to address because I don’t want to misrepresent it was did that invitation have something to do with making you feel more welcome or lessening the feeling of annoyance?

Holt:

Well, I personally didn’t have any feeling of annoyance. I was just trying to figure out how to do physics without totally being engulfed in ten years of building stuff at JLab. [Laughs]

Westfall:

Good! Okay.

Holt:

I was drawn in anyway from the beginning because we were setting up the CEBAF Internal Target Working Group. We were meeting there every several months.

Westfall:

Right. So you were already fine.

Holt:

Yeah, I was fine with it. The issue at that time was that the project wasn’t even approved, and you had to ask when would it be, right? And I was a young scientist and people were already criticizing me because I didn’t have many publications in the early eighties while I’m working on that GEM proposal. [Laughs] So I felt like I had to do physics now, and I couldn’t wait ten years or whatever it was going to take to realize this dream. So I was happy to work on the internal target program because I knew I could make a contribution to JLab that way, or to CEBAF that way. Plus at the same time, there were other rings where you could actually get data now. So that’s the way I looked at it.

Westfall:

So at the time of the meeting at O’Hare that sparks the… But that drew you in. That helped draw you in.

Holt:

That helped draw the whole group in. You know, Don and Hal were never a part of that CEBAF Internal Target Working Group. They were busy with other things, frankly. Don was immersed in E665. Right after the internal target working group ended at CEBAF, I basically put most of my effort toward NPAS, which was the SLAC program. I was actually drawn off to Novosibirsk as well at the time. So yes, in the O’Hare meeting, Hal came back and reported to the group that we’d been made an offer that we’d have a hard time refusing. In fact, the offer was —

Westfall:

This is Hal Jackson.

Holt:

Yes. Hal Jackson basically presented the offer: they wanted us to collaborate with Urbana, build a major piece of equipment, possibly a second arm to go in Hall C. They would provide the high momentum spectrometer already planned in Hall C, but they needed a second arm. There was some fear that Hall C could be completely descoped if good groups didn’t join in there and help build the facility.

Westfall:

Right. You betcha!

Holt:

Then Hal told us that Grunder said one thing that was intriguing. He said, “We’ll give you all the beam time you want,” and so we’re asking, “How could he do that?”

Westfall:

It turned out he couldn’t. [Laughter]

Holt:

Yes. So I think Hal… I don’t remember exactly; you’d have to talk to Hal about this. But I think Hal contacted Dirk Walecka and asked, “Is this really… This promise of all the beam time we want —”

Westfall:

Walecka, who was the scientific director who would have been in charge of the scientific program which included a program advisory committee that was[laughter]… that was to determine who got time.

Holt:

Yes. But anyway…

Westfall:

And Walecka said no.

Holt:

And Walecka said, “No. You’d have to go through the PAC and the normal process just like everybody else, and certainly we’d be happy to have you do that.” But I wasn’t put off by that because I was sort of half expecting that. Also, I thought, “Well, if we put something forward, let’s put something forward that will be exciting and good physics. So why worry about what the PAC will accept or not? Of course they’ll accept it!”

Westfall:

Right. You had confidence.

Holt:

Right, at the time. So then we formed these meetings with UIUC. Some of the meetings would be here, and some would be in Urbana and we’d interchange. At some point, it broke down, and I think the reason it broke down was Urbana had a definite idea in mind about what they wanted as a second arm. It was some complicated out-of-plane spectrometer that had multi detectors. I think they called it STAR or something like that. It had a relatively small solid angle. I thought that it made a poor match for the high momentum spectrometer. And when I looked at the physics case they were trying to build for the out-of-plane measurements, I just didn’t see it as being a major driver. Basically, I came to the conclusion that what we ought to do is just build a large acceptance spectrometer, roughly half the momentum of the HMS, almost close to our original conceptual design for that hall. It wouldn’t have to go out of plane, and you could do a lot of interesting physics with that. Finally, I wrote an email or a letter to Hal saying, “I’m involved in SLAC and Novosibirsk. I’m going to these meetings, and they’re not budging on the physics or spectrometer design. I think I’m wasting my time. I think we ought to put forward just a simple spectrometer arm.” A short-orbit spectrometer can do kaon physics, pion physics, (e,e’p) and whatever. Make it fairly easy to build and fairly inexpensive compared to the other designs. Make it room temperature so we’re not getting into the superconducting magnets.

Westfall:

Any fancy technology, right.

Holt:

Eventually we made it even simpler than I had actually hoped. But we adapted the reverse Enge splitpole design that had been used at LAMPF for the medium resolution spectrometer. So it was basically a copy of that spectrometer with a lot of shielding. I think there was a shootout at CEBAF in about 1990 where Hal presented his design and the physics you could do with it, and Costas Papanicolas —

Westfall:

You don’t happen to know how to spell that name, do you?

Holt:

No.

Westfall:

Papanicolas.

Holt:

I can try. Papanicolas.

Westfall:

Okay. Good for you. Okay.

Holt:

And I’m not sure if there are two —

Westfall:

He was at Urbana, right?

Holt:

He was at Urbana, and I think he made the presentation for Star. I think some committee decided that it should be our design. But a compromise —

Westfall:

So the STAR design lost. [Yes.] And the Argonne design won.

Holt:

But then CEBAF said, “Well, let’s put on the condition that it can go out of plane. The SOS is a small enough arm, you can just lift it out of plane, and if they (UIUC) want to do some physics like that, they can do it.” As far as I know, it never went out of plane for an experiment. So then we were locked in —

Westfall:

Okay, here is the equipment plan from 1990. Here’s the whole document about Hall C. I don’t know if that…

Holt:

Yes, this was the reverse Enge splitpole here, the SOS, and detector package. I had responsibility —

Westfall:

That is Figure 2, 3. I can’t see that far.

Holt:

Figure 2.

Westfall:

Figure 2. Okay.

Holt:

Yes. So Hal was responsible for providing that SOS, and I was responsible for interfacing with all the institutions that were building detectors for it and making sure there’s a frame that holds them up in the right location. So that was basically the way that came about. In ‘94, I went to Urbana for six years.

Westfall:

Oh!

Holt:

Yes. One of the problems with the UIUC group was that they lost key personnel because both Eisenstein and Cardman left.

Westfall:

To go to JLab. [Right.] Eisenstein left to go to NSF. No. Where? To NSF? Am I right?

Holt:

Yes, right. NSF.

Westfall:

To NSF, National Science Foundation. [Yes.] And Larry Cardman left to go to JLab.

Holt:

JLab, yes.

Westfall:

To be John Domingo’s deputy.

Holt:

Right. Then Costas Papanicolas was leaving, so there were three…

Westfall:

Of their top people.

Holt:

Yes, and so they contacted me and said, “The only programs we have are some out-of-plane experiments at Bates, and some Saskatoon experiments that are shutting down. We need somebody to move us into the JLab and, possibly HERMES modern day experiments.” So finally I agreed to go there and help them do that. From there, working with Ron Gilman at Rutgers and Haiyan Gao and maybe even — [How to spell Gao’s name] She was my first post-doc at Urbana, and she’s chair of the Duke Physics Department now.

Westfall:

Oh, cool.

Holt:

So we made something like five proposals to JLab during that period, five successful JLab proposals.

Westfall:

Step back. So what year was that? ‘94?

Holt:

‘94 to 2000 I was there.

Westfall:

Okay. So to what extent, if any, did you help in the building of the Hall C equipment?

Holt:

Well, I had responsibility for the SOS detector frame. So I saw to it that it was designed, built and Hall C users interfaced to it. That was basically our business, mainly getting the design and seeing to it that it got built. It was a fairly massive apparatus even though it was a small spectrometer. Then in ’95, Don’s experiment was first. Actually, mine was supposed to be first, but the cryotarget didn’t work. My experiment was second, and we commissioned the cryotarget. That was no small problem. There were some things missing that should have been there on the cryotarget, like an expansion tank. We blew several loads of liquid deuterium out the stack before they realized that they should actually put that back in the design! It was interesting.

Westfall:

Yeah. As Larry explained to me, in those — First of all, he and Don both said that the reason that Hall C is the first to go to do experiments is that you wanted the least complicated equipment to be built. It’s going to be built first, so you want it to do experiments first, and you want the simplest experiments that will still be good experiments to get data.

Holt:

Right.

Westfall:

So somehow out of that calculation, they came up with your and Don’s…

Holt:

Right. That’s right. They wanted my experiment mainly to commission the cryotarget, I think, and they wanted Don’s to commission the spectrometers. So it worked out quite well.

Westfall:

So it was commissioning. It was a combination of commissioning and taking data.

Holt:

Oh, indeed. It was a devil of a time to run and to analyze data because of the commissioning aspect and because the spectrometers actually had to be calibrated. That had never been done before, so we participated in that.

Westfall:

Just out of curiosity, what was it like to do experiments at JLab compared to all other laboratories?

Holt:

Well, JLab was a dream compared to the others. If you compare it to SLAC, SLAC was okay, but as they say, “We don’t give coulombs; we give hours.” It didn’t have a high running efficiency. My recollection is that it’s something like 50% for the accelerator, maybe even less if you ask me really. So you could get a month, but it only turns out to be two weeks of beam. We would complain to Dick Taylor, and he would say, “No. We give hours, not coulombs of beam.” [Laughs]

Westfall:

Because it was mainly for high energy physics.

Holt:

Yes.

Westfall:

And you were…

Holt:

Yes. That was another problem. At Bates, the accelator didn’t run well, when we ran the t20 experiment. We ran the first experiment in the South Hall. The South Hall was a new hall, and it was very, very difficult because those spectrometers hadn’t been completed or commissioned, either. Bates did not run well at that point in time. So in many ways, CEBAF was a dream. Of course, in the beginning it was a little rocky, but later on, it was just a dream to run there because they had designed things correctly. There was a lot of shielding in place. The beam was very high quality, very low halo on the beam, and it was reliable. So to my mind, this was a dream come true. Jefferson Lab was purely a dream come true that they built an accelerator that advanced us in every area of parameter space that we could push on in terms of the accelerator and the experimental equipment, and it ran well. We were not used to that.

Now LAMPF actually was a proton machine, but it ran exceedingly well also. In fact, when I was saying, “You know, we really need these three experimental areas,” I had LAMPF as a model in mind where it could run several experiments at once. Also, I really believed that if you build a facility, you need at least two detectors. For example, HERA is a beautiful case. If you had only one detector at HERA, we wouldn’t have anywhere near the quality of data we have now because when these two detectors disagreed, they figured out the problem. If you don’t have at least two detectors, you can be way out in left field.

Westfall:

How about the early formation? One of the things that interests me about JLab is that you have these three — Each hall has a very separate mode of collaboration with both Hall A and Hall B being much more like the standard high energy physics model of a collaboration.

Holt:

Yes.

Westfall:

And Hall C…

Holt:

Yes. Hall C doesn’t have a strong collaboration structure like high energy physics, but they work well as a collaboration. Basically in substance, they accomplish the same things, I think, without having to have a strict set of by-laws that people have to conform to. I think I never saw that much difference operationally between Hall A and Hall C. Of course, I’m not a member of the Hall A collaboration, although I’ve run experiments there.

Westfall:

In terms of being able to get physics done.

Holt:

Right. Hall B is a little more strict, I think. But they have several levels of collaboration there. You can be a full collaborator where you obey a certain set of rules and take so many shifts a year and do whatever the requirements are, and then there’s another level. I’m not sure what they call it, but you just work on one experiment and go away with the data.

Westfall:

So that that means that your name wouldn’t be on every publication, for example.

Holt:

Right. Exactly.

Westfall:

How about Hall A? When you worked in Hall A, you did an experiment there, but you weren’t a member of the collaboration.

Holt:

Right.

Westfall:

So they had a similar kind of arrangement so that…

Holt:

Well, I don’t know if it was formal, but operationally, yes. They never pressured me to join the Hall A collaboration. I may have done it off and on briefly, but I don’t know. It may depend critically on the hall leader and how they govern it. If they want everybody who runs in Hall A to be a Hall A collaborator, join that collaboration, I suppose they could do that. The hall leader could enforce that. But I don’t think they really have done that.

Westfall:

Who was the hall leader when you ran? Was it Kees?

Holt:

Kees de Jager, yes. He encouraged me. Actually, he encouraged me once to join the Hall A collaboration.

Westfall:

How to spell name —

Holt:

It’s really C. W. de Jager, but he’s called Kees.

Westfall:

So you came and you — Let’s just circle back a bit to your Hall C. So you did the second experiment in Hall C.

Holt:

Yes.

Westfall:

It was meant to be the first, but then you had trouble with the target, and then you did the second.

Holt:

Yes.

Westfall:

Then did you continue doing experiments at JLab?

Holt:

Well, that ran in ‘96, and by then we already had two or three other proposals in for JLab. And so we were running additional experiments not too long after that.

Westfall:

Here, by the way, is the list of experiments through the time of about 2000, Don said.

Holt:

Okay, okay. Yes, yes.

Westfall:

You had this great quote and I’m going to quote you on it, how that JLab was “a dream come true.”

Holt:

Yes.

Westfall:

So I just would like to go back. That’s perfect because my controlling metaphor has to do from dreams to reality — how dreams are set into concrete. So the initial experiments that you wanted to see with GEM — and I could give that back to you if you happen to need to see it — how many of them run in this first phase? How is it different? How is the experimental program, once it got up and running, different from what you initially envisioned?

Holt:

Well, let’s see. Oh, by the way, Grunder sent a Christmas card. I framed it here. This is showing our JLab data.

Westfall:

Oh! “Dear Roy, I wish you and your family the very best. The first data has a very special appeal. Santa liked it, too. Thanks and best wishes, Hermann.”

Holt:

Yeah. This is showing the SLAC NE8 data, and here was NE17. You see up to 4 GeV. There’s no scale on the axes. You see it basically behaves a scaling law. [Laughs]

Westfall:

For the tape recorder, “Dear Roy, I wish you and your family the very best. The first data has a very special appeal. Santa liked it, too. Thanks and best wishes, Hermann.” Then it has this picture of the data that you are saying follows the scaling.

Holt:

Yes.

Westfall:

That is, that EMC scaling?

Holt:

Well, no. It’s a perturbative-like scaling.

Westfall:

A perturbative-like scaling. Then he has this — and this is before the era of Photoshop, so somehow he has Santa in his sleigh to approximate the curve. [Laughter]

Holt:

[Laughter] Yes. So you can see what we were talking about and what was exciting us. We put in two or three more proposals along this line to measure the polarization and even higher energy, up to 6 GeV. So in terms of what we proposed at GEM…

Westfall:

Compared with this…

Holt:

Well, of course we didn’t know about photodisintegration of the deuteron then. This is something that came up actually in ‘83 when Brodsky and Hiller’s paper came out. The experiment that was done was t20 and electron-deuteron scattering. Serge Kox at Grenoble led that experiment. We did the first experiment on this at Bates, and John Cameron and his colleagues came along and built a better polarimeter and did a second experiment at Bates and then a French group led by Kox built an even better polarimeter and did an experiment at JLab. So that was one thing that got done, and it showed that t20 in e-d elastic scattering went nowhere near the perturbative limit at all. It looked like the meson exchange theory, and so that was quite interesting. GEN, the electric form factor of the neutron was another big issue that we thought was really important. One of the main reasons we were building this facility was to get at the electric form factor of the neutron. Those kinds of experiments I think were done in fairly early days.

There were surprises that arose. By 2000, there were a couple of surprises that are driving the field even today, and one was the electric form factor of a proton. The polarization transfer experiments you could now do with JLab showed that the electric and magnetic form factors aren’t the same. This is disagreeing with the SLAC or Rosenbluth version of that measurement. We never thought that this would be an important experiment, but it turns out actually that it probably could be the most important experiment that JLab has performed to date. The strangeness form factors we never envisioned, and those were done. If you measure the strangeness content of the form factors and you measure the electric form factor, magnetic form factor of the proton and neutron, that allows you to unravel the underlying quark contribution to the proton form factor. That’s been really a very good test of underlying theoretical quark models of the nucleon. There’s more of that to come in the 12 GeV era.

The other was the discovery of the Sivers effect by HERMES. In fact, those two discoveries together convinced, I think, most people that quarks have orbital angular momentum in the nucleon. That’s driving all of the future transverse momentum dependent experiments at JLab. It’s driving another bunch of proposals.

Westfall:

Well, you might compare GEM and then post-GEM, you know what you thought at the time. By the time you start building, or even at the time in the mid ‘90s when you’re taking the first data.

Holt:

Well, I actually think JLab’s done most of what we were proposing in that proposal.

Westfall:

In the GEM proposal.

Holt:

Yes. One was just form factors of the light nuclei, for example, and deuteron form factors, as A(Q2) and t20, helium-3, helium-4, form factors of the light nuclei, the form factors of the nucleon. We didn’t have the proton in mind because we thought SLAC had cleaned that up, but we had the neutron in mind. The N to delta transition, I think Don promoted N → Δ transitions. I think that that’s been done.

Westfall:

That is N → Δ.

Holt:

Yes, nucleon to delta. That was a very interesting experiment. Let’s see. What else do we have? Ah, color transparency, (e,e’p) of course. (e,e’p) was a big program that Don started at Bates. He started experiments at Bates, and this was carried on at SLAC with Milner, who proposed that as a way of observing color transparency, experiment NE18. Then Don proposed it at JLab, and that was done, a very interesting set of experiments. Let’s see. Hmm. Well, (e,e’p) experiments in nuclei we had proposed. I think some examples of that had been done, Mougey-like experiments. I would have to say probably most of the things that have been done we didn’t think of at the time. [Laughs] You know, literally.

Westfall:

Because once you started using this tool, you found new things to explore? Was that…

Holt:

Oh, yeah. (e,e’K), something Ben Zeidman proposed from Argonne, some of those experiments were done. Actually, the Japanese group took that over with a vengeance and looked at hypernuclei. I thought that would be more interesting than it turned out to be. As I say, these parity-violating electron scattering experiments were interesting, getting at the strange quark content of the proton. Bob McKeown started that. In fact, he credits Walecka — Walecka was here for a year giving us lectures on electron scattering, and McKeown was here at the time. He went to Walecka’s lectures, and he credits Walecka with having piqued his interest in parity-violating electron scattering.

Westfall:

When you say that they were both here, you mean they were visiting scientists at Argonne?

Holt:

Well, McKeown was either a post-doc or a staff member. He was a graduate student here with Gerry Garvey, and then I think he stayed on probably as a post-doc for a very short time and went to a staff member or went directly to staff member. I don’t remember. So he was here for about a year after he graduated probably mostly in a staff position.

Westfall:

So that meant he was a graduate student at the University of Chicago?

Holt:

That’s a good question.

Westfall:

Anyway, I can find that out.

Holt:

He started out at Princeton. Garvey came from Princeton, and he may have been a student at Princeton.

Westfall:

Okay. Gotcha. That happens. But Walecka. You mean Walecka came…

Holt:

Walecka came on sabbatical here for about a year.

Westfall:

Oh. In about what time?

Holt:

It was about, I would say, ‘82.

Westfall:

Interesting. Okay.

Holt:

And he gave us a beautiful series of lectures and produced a book of lecture notes that we published as an Argonne internal report. We could probably get that somewhere, probably dig that out. Anyway, McKeown went to those lectures and learned about parity-violating electron scattering, and he credits Walecka with starting him along the lines of thinking about that and these strangeness experiments. McKeown proposed the sample experiment at Bates at the time as a way to get at the magnetic strangeness form factor. Then later, Doug Beck proposed G0 at JLab, and I see that here in 1991.

Westfall:

So that’s a cute backstory for G0.

Holt:

Yes, yes. When I went to Urbana, there were still problems of getting G0 started and funded, and I had to spend some hours talking with Jack Lightbody about it when I was there. However, Doug did the heavy lifting for the funding and the experiment. So yeah. Okay. I’m not sure what more I can say.

Westfall:

This is good!

Holt:

Some of these are our proposals.

Westfall:

Well, this would be a good ending point. I feel like I have learned a lot. Thank you!