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Stuart J. Freedman was an experimental physicist with a broad sweep of talents and interests that centered on nuclear physics but also spanned particle physics,.
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A Biographical Memoir by R. G. Hamish Robertson
©2014 National Academy of Sciences. Any opinions expressed in this memoir are those of the author and do not necessarily reflect the views of the National Academy of Sciences.
Anne (Sklar) Freedman—and attended schools in Beverlywood. By all accounts he was a strong student and a “normal” teenager, with a penchant for ruffling establishment feathers whenever possible. His occasional minor run-ins with the law and hilarious interactions with bureaucracies became the stuff of good stories later in life. He also was athletic, swimming competitively and playing football. Stuart entered UC, Berkeley, in 1961, graduated with a B.S. in engineering physics in 1965, and decided to stay on for graduate work in physics. He and Joyce Schechter, who had known each other since high school, married on December 16, 1968.
After working in theoretical particle physics under Charles Zemach for about a year, Stuart sought a more satisfying experience in experimental physics and approached Eugene Commins, who, together with student Carl Kocher, had some years before
Stuart J. Freedman was an experimental physicist with a broad sweep of talents and interests that centered on nuclear physics but also spanned particle physics, quantum mechanics, astrophysics, and cosmology. As a graduate student at the University of California, Berkeley, he carried out a crucial test of the Einstein-Podolsky- Rosen (EPR) argument that quantum mechanics was an incomplete theory; Stuart showed that EPR’s postulated local hidden variables did not explain experimental data, whereas quantum mechanics did. Stuart was an early and continuous leader in the search for neutrino oscilla- tions, and in the KamLAND project he determined which of several possible solutions the correct one was. He also was noted for several instances in which an incorrect result with major implications was neutralized. Perhaps the most famous case involved the 17-keV neutrino.
January 13, 1944–November 10, 2012 Elected to the NAS, 2001
By R. G. Hamish Robertson
in conflict with the EPR recourse to hidden variables. A picture of Stuart Freedman with the apparatus is shown in Figure 1.
In bringing this experiment to its successful conclusion, both Freedman and Clauser played vital roles. The idea to do the exper- iment and the initiative to do it in the envi- ronment of the experienced Berkeley group, came from Clauser. The actual experimental work was, for the most part, Freedman’s. The Freedman-Clauser experiment was a classic, the first in a long series of important tests of such fundamental concepts as locality and realism in the framework of quantum mechanics. Moreover, its significance appears to have grown with time. Asked why he did not continue his highly successful expedition into the foundations of quantum mechanics, Stuart responded that he found the field to have attracted more than its share of people at the fringes of science, and he did not find this aspect enjoyable.
Completing his dissertation work at Berkeley in 1972, Stuart took an instructor position at Princeton University, where he worked with Frank Calaprice. Calaprice had developed methods for studying the weak interaction, using polarized 19 Ne that had been produced in the Princeton cyclotron, which enabled researchers to address interesting questions such as whether so-called “second-class” currents existed in the weak interaction or whether time-reversal symmetry was violated. After completing two publications with Calaprice (1975 and 1977), Stuart moved toward more specifically nuclear problems.
The presence of Gerald Garvey at Princeton influenced not only Stuart but also a large number of other young physicists at a similar stage in their careers. The year 1975– alone brought Eric Adelberger, Rosemary Baltrusaitis, Thomas Bowles, Robert Cousins, Robert Del Vecchio, Carl Gagliardi, John Greenhalgh, Jerry Lind, Robert McKeown, Anthony Nero, Michael Oothoudt, Hamish Robertson, Ben Svetitsky, Robert Tribble, Frederick Zutavern, and others together in an energetic and merry group. The work on isospin-symmetry violation in nuclei that Stuart led was not particularly memorable, but Stuart emerged as the glue that kept most of this group of physicists together throughout
Figure 1. Stuart stands with the aparatus to test Bell’s inequality.
their careers. Steve Girvin was a graduate student at Princeton then as well, and he taught Stuart and others in the group to fly sailplanes, a pastime that Stuart enjoyed for years afterward.
In 1976 Stuart accepted an assistant professorship at Stanford University in order to work with Stanley Hanna’s group, and he remained at Stanford until 1982 without receiving tenure. His relationship with Hanna was difficult from the beginning, reflecting their very different views on the level of authority that should appropriately be exerted by senior personnel within a research group.
While at Stanford, Stuart, together with Alan Litke, developed the first experiment—a fractional-charge search (1982)—to run on the new electron-positron storage ring PEP; from this effort, Jim Napolitano earned his Ph.D. under Litke. In 1978 Stuart was awarded an Alfred P. Sloan Foundation Fellowship, his first substantive recognition by the larger physics community. These successes aside, the experience at Stanford was discouraging, but his mentor Gerald T. Garvey told him, “Stick around, and sooner or later someone will make a mistake.” Good to his word, Garvey, who had just moved to Argonne National Laboratory, recruited Stuart. But Stuart claimed not to trust Garvey and insisted that his mentor should write him a letter promising his good faith in the matter. The letter is reproduced in its entirety in Figure 2 and illustrates, among other things, the irreverence of both individuals toward the bureaucratic process.
At Argonne, Stuart began to receive anew the resources and encouragement that allowed him to flourish once again in physics. His work on the beta spectrum of 8 B (1987) and on the neutron capture cross-section of 3 He (1989) is the basis of modern calculations of the shape of the solar high-energy neutrino spectrum. The Sudbury Neutrino Obser- vatory experiment, which later demonstrated that the “solar neutrino problem” was caused by new-neutrino physics, relied on the Napolitano-Freedman-Camp spectrum (confirmed with new data by Stuart’s group in 2003) to pin down the allowed regions of parameter space for this phenomenon. The solar neutrino problem was that the measured flux of neutrinos was less than half as large as expected, based on the rate of energy production by the sun; this apparent deficit of neutrinos was shown by SNO to result from electron neutrinos converting to mu and tau neutrinos on their journey from the sun to Earth. Such neutrino “flavor” conversion, a manifestation of quantum-mechanical neutrino oscillations, requires that neutrinos have non-zero mass.
Stuart played a major role in experiment E645—a search for neutrino oscillations—at the Los Alamos National Laboratory’s Meson Physics Facility. This was a large and
complex experiment with a somewhat fractious collaboration. Stuart’s group had respon- sibility for the 670-ton active veto to reject cosmic rays (1983). It consisted of a large annular steel tank, filled with liquid scintillator, and photomultiplier instrumentation. Stuart recounted with wry amusement that they had specified to the manufacturer that the tank “must be helium-leak tested.” Yet on delivery, the tank was found to leak like a sieve; in fact, many of the welds were missing entirely. Stuart reminded the company about the requirement, and the response was, “We did test it. It leaked.” But the repaired instrument was completed on time, performed flawlessly (1993), and was subsequently incorporated into a successor oscillation experiment, LSND. This was Stuart’s first foray into neutrino-oscillation physics, a field to which he would return 10 years later with spectacular impact.
The beta decay of the free neutron provides a great deal of information about the weak interaction and the fundamental symmetries of nature. The direct and unob- structed access to such basic questions was attractive to Stuart, who was instrumental in conducting a series of experiments that set the standard in the field. The research reactor of the Institut Laue-Langevin in Grenoble, France, was the international venue for fundamental neutron physics, and it was there that Stuart formed a close collabo- ration with Dirk Dubbers. The “Perkeo” detectors they built yielded precise new data on the beta asymmetry of the neutron (the correlation between the neutron spin and the electron momentum directions), which in turn provided the ratio of the strengths of the vector and axial-vector parts of the interaction (1988). The same apparatus was used to determine the neutron lifetime with a novel approach, although precision was limited. The neutron guide hall at the NBS Reactor in Gaithersburg, MD, was another attractive site for this kind of research, and an experiment originally proposed by Thomas Bowles in 1982 to measure the so-called D coefficient in neutron beta decay was carried out there by Stuart and his colleagues. The parameter D is non-zero only if time-reversal symmetry is violated; an upper limit on its size was found (2012). The D-coefficient project began in 1995, after Stuart had moved back to Berkeley.
In 1985, John Simpson and his student Andrew Hime at the University of Guelph in Ontario were exploring a novel method for measuring the mass of the neutrino; they were motivated by a 1981 paper of a Russian group, which reported that the electron neutrino had a mass of 30 eV. To address this question in a way less dependent on systematic uncertainties, Simpson and Hime implanted a silicon detector with tritium from an accelerator and measured the beta spectrum from its decay. The classic method of beta decay relies on a change of shape of the beta spectrum near the “endpoint,” where
the electron takes all the energy available in the decay. If the neutrino has some rest mass, the electron cannot take that last bit of energy, and the spectrum shows it. They did not find evidence for or against the Russian result but did observe a striking deviation in the shape of the spectrum at an energy 17-keV below the endpoint. A neutrino of such a mass was completely unexpected. Soon laboratories around the world were racing to check this evidence for a 17-keV neutrino weakly admixed with the electron neutrino. To much surprise, supporting evidence was forthcoming from many different isotopes: (^14) C, 35 S, and 63 Ni, as well as tritium. Some experiments, however, particularly those using
magnetic spectrometers, did not produce evidence for a 17-keV neutrino, although the sensitivity and robustness of those experiments was challenged with some success.
Into this confusing scene came Stuart Freedman, a physicist with a justly earned repu- tation for his ability to master systematic uncertainties and minimize them. Stuart was aware of the existence at Argonne of a unique electron spectrometer, designed and built by Zbigniew Grabowski, in which the radioactive source was positioned in the high magnetic field of a superconducting solenoid and the silicon detector was in a low-field region. In that arrangement, electrons from the source cannot scatter from the apparatus before entering the detector, an effect that Stuart suspected (correctly, as it transpired) was responsible for the spectrum modification in many cases. Working with a University of Chicago undergraduate student, Justin Mortara, Stuart carried out a measurement of the spectrum of 35 S and published the result in 1993. He and Mortara saw no evidence for the spectrum distortion, and they further showed by adding a trace of a different isotope, 14 C, that they would have seen it had it been present. Their result was universally accepted as definitive and the question was settled: there was no 17-keV neutrino. Subse- quent work by Hime and others disclosed the role of scattering, as Stuart had surmised. The cause of the original Simpson-Hime result, which also was immune to scattering, was probably attributable to theoretical uncertainties.
The year 1989 saw another flurry of excitement in physics when Martin Fleischmann and Stanley Pons, and, contemporaneously, Steven Jones, claimed evidence for cold fusion in the electrolysis of heavy water on palladium electrodes. Fleischmann and Pons reported excess heat production, and Jones reported the production of neutrons, both indicators of fusion reactions. Many researchers attempted to duplicate the results, generally without success. Without setting foot in the lab, Stuart noticed the finger- print of a flawed procedure in the data. Specifically, the neutron data of Jones had low statistics and the deviation of the points from background was positively correlated with the uncertainty on each point. It is easy for an experimenter to obtain such an effect
cochaired with Boris Kayser. He also served as cochair with Ani Aprahamian of the NAS Committee on the Assessment of and Outlook for Nuclear Physics, which issued the 2010 NAS Decadal Report on Nuclear Physics.
Stuart’s final two decades at Berkeley were a productive and rewarding time for him. He divided his research time between fundamental symmetries experiments on the local 88-inch cyclotron and large collaborative experiments elsewhere.
Just as neutrons can be polarized and studied as they decay, so is it possible to polarize radioactive atoms in order to explore the nature of the weak interaction. Stuart was an early adopter of lasers to trap and polarize radioactive nuclei for fundamental-inter- action experiments, and 21 Na was the focus of the program because of the ease with which it could be produced and trapped for study. The magneto-optical trap (MOT) for the experiment had an intriguing and beautiful shape, with magnetic coils and optical windows for laser beams. After his death, the first MOT that he built became the funerary urn for Stuart’s ashes.
Another experiment that took advantage of the cyclotron’s beams was a study of the beta decay of 10 C. It is one of a class of “superallowed” nuclear decays that collectively provides the most precise data on the Cabibbo angle, a measure of the rotation, or misalignment, of the strong and weak interactions between quarks. The origin of this misalignment is still a mystery and lies outside the standard model. It had been known for more than 20 years that the key decay to measure was 10 C, because it is the least affected by Coulomb and nuclear corrections, but the relevant branch is weak and the measurement fraught with experimental difficulty. Stuart devised an ingenious way to do the measurement—with internal calibrations that removed most of the systematic uncer- tainties. After many years of improving the technique with his colleague Brian Fujikawa, the final precision they obtained (1999) was good—but still not a challenge to the world average for the parameter measured with this and other nuclei.
The search for neutrino oscillations was poised to make the transition to discovery in the last few years of the 20th century. By 1997 there were indications from experiments that the solar neutrino problem could not be explained by astrophysics and that new neutrino physics was required. Experiments with water-based Cherenkov detectors built to search for proton decay were yielding puzzling results for what should have been a straight- forward background process—the interaction of atmospheric neutrinos. Only about half
the expected number of muon-flavor interactions were being seen, whereas the number of electron-flavor interactions came out right. Then, in 1998, the Super-Kamiokande detector at the Kamioka mine in Japan, a huge water-based Cherenkov detector, gave conclusive evidence for neutrino oscillations: a characteristic path-length dependence for the survival of atmospheric muon neutrinos produced on the other side of the planet.
Physicist Atsuto Suzuki noticed that Kamioka happened to be near the center of a rough circle formed by dozens of Japanese power reactors. The radius of this circle, 180 km, and the typical energy of electron (anti) neutrinos from reactors, meant that one particular choice of neutrino-oscillation parameters that could explain the solar neutrino problem would also give a pronounced signature in a suitable detector in Kamioka. Visiting the area in 1997, Giorgio Gratta began a collaboration with Suzuki and gathered several U.S. groups to participate in building a liquid scintillator detector at the site. Stuart became American cospokesman with Gratta in 1998, bringing his Berkeley group into the collab- oration, and they worked successfully to interest the U.S. Department of Energy (DOE) in providing the necessary support. Completed in a relatively short time, the project, called the Kamioka Liquid Scintillator Antineutrino Detector (KamLAND), would turn out to be a stunning success.
In 2001 the solar-neutrino problem was resolved in favor of neutrino flavor change by the Sudbury Neutrino Observatory in Canada. The SNO detector showed definitively that electron neutrinos did indeed undergo flavor change, but it could not distinguish between three possible choices for the oscillation parameters. In 2003 KamLAND narrowed the choice to a single possibility, the “large-mixing-angle” solution. With more data, the collaboration was later (2008) able to display, at Stuart’s urging, the results in a dramatic plot that revealed for the first time the oscillation phenomenon directly. The detector was capable of detecting antineutrinos from radioactive elements inside Earth as well, and did so.
The success of these experiments focused attention on the one remaining unknown parameter in neutrino flavor-oscillation physics, a parameter called θ 13 , which essentially describes the amount of electron flavor mixing with other flavors over relatively short baselines. The parameter has special importance in neutrino physics because it must be nonzero in order to determine whether neutrinos respect the symmetry CP (equiva- lently, time-reversal invariance). Violation of CP symmetry by neutrinos would open a
into low-temperature calorimetric methods of measuring nuclear decays existed in Milan, Italy, led by Ettore Fiorini, and when he and his team sought to increase the scale of their 130 Te double-beta-decay detector from a few kilograms to hundreds of kilograms, they invited American groups to join. Stuart became the U.S. spokesman for this project, CUORE, and, as he had done so effectively in other cases, engaged the interest both of the U.S. DOE and National Science Foundation. When he died, the experiment was making good progress toward construction of a complete tower of ultrapure TeO 2 crystals, the first of many for the scaled-up detector.
Stuart enjoyed research and teaching, but most of all he enjoyed working with students and postdocs. His Berkeley students were Jason Amini, Thomas Banks, Christopher Bowers, Jason Burke, Daniel Dwyer, Laura Kogler, Laura Lising, Zhengtian Lu, Justin Mortara, Thomas O’Donnell, Mary Rowe, Nicholas Scielzo, Jason Stalnaker, Lindley Winslow, and Wesley Winter.
Figure 4. Portrait of Stuart by his sister, Ina. (Courtesy Joyce Freedman.)
A modest man, Stuart wrote at the time of his election to the National Academy of Sciences:
I am an experimental physicist interested in understanding the nature of the fundamental forces and the basic composition of subatomic matter. I enjoy the experimental challenge of high-precision experiments exploiting atoms and nuclei as laboratories for studying fundamental questions. Despite their complexity, nuclei and atoms reflect the basic symmetries of the underlying physics governing the interactions among the more fundamental quarks and leptons. Much of my work involves searches for unexpected phenomena, new particles or interactions that might indicate a shortcoming in the current theoretical description.
Recent experiments in my laboratory exploit new methods of atom and ion manipulation to make very precise measurements in nuclear beta decay. These experiments question the basic structure of the weak inter- action. We are also conducting an experiment with a massive under- ground reactor antineutrino detector, which addresses basic questions about the masses of the neutrinos.
Stuart passed away on November 10, 2012, at the age of 68, from complications of amyloidosis. He was in Santa Fe, NM, attending a conference on the uses of ultracold neutrons for fundamental-symmetry research, surrounded as he was throughout his life by friends. His death came unexpectedly to most people, as Stuart had kept the condition largely to himself. He left behind a loving family—his sister Ina Scheid, wife Joyce, son Paul, daughter-in-law Emily Van Allen Freedman, and grandchildren Evie and Jonah—a legion of friends and admirers, and proof that integrity can travel hand- in-hand with achievement.
1990 With D. Krakauer. Biases in cold fusion data. Nature 343:703–703.
1993 With B. K. Fujikawa et. al. Limits on neutrino oscillations from anti-electron-neutrino appearance. Phys. Rev. D 47:811–829.
With J. L. Mortara, I. Ahmad, K. P. Coulter, B. K. Fujikawa, J. P. Greene, J. P. Schiffer, W. H. Trzaska, and A. R. Zeuli. Evidence against a 17-keV neutrino from 35 S beta decay. Phys. Rev. Lett. 70:394–397.
1999 With B. K. Fujikawa, S. J. Asztalos, R. M. Clark, M.-A. Deleplanque-Stephens, P. Fallon, J. P. Greene, I.-Y. Lee, L. J. Lising, A. O. Macchiavelli, R. W. MacLeod, J. C. Reich, M. A. Rowe, S.-Q. Shang, F. S. Stephens, and E. G. Wasserman. A new measurement of the strength of the superallowed Fermi branch in the beta decay of 10 C with GAMMASPHERE. Phys. Lett. B 449:6–11.
2003 With K. Eguchi et al. First results from KamLAND: Evidence for reactor anti-neutrino disappearance. Phys. Rev. Lett. 90:021802-1–021802-6.
With W. T. Winter, K. E. Rehm, I. Ahmad, J. P. Greene, A. Heinz, D. Henderson, R. V. F. Janssens, C. L. Jiang, E. F. Moore, G. Mukherjee, R. C. Pardo, T. Pennington, G. Savard, J. P. Schiffer, D. Seweryniak, G. Zinkann, and M. Paul. Determination of the (^8) B neutrino spectrum. Phys. Rev. Lett. 91:252501-1–252501-
2004 With B. Kayser and other members of the APS Multi-Divisional Neutrino Study. The neutrino matrix. Washington, DC: American Physical Society. Available online at www.aps.org/policy/reports/multidivisional/index.cfm, accessed on May 16, 2014.
2008 With S. Abe et al. Precision measurement of neutrino oscillation parameters with KamLAND. Phys. Rev. Lett. 100:221803-1–221803-5.
2012 With T. E. Chupp et al. Search for a T-odd, P-even triple correlation in neutron decay. Phys. Rev. C 86:035505-1–035505-22.
2014 With D. E. Artusa et al. Searching for neutrinoless double-beta decay of 130 Te with CUORE. arXiv 1402.6072.
Published since 1877, Biographical Memoirs are brief biographies of deceased National Academy of Sciences members, written by those who knew them or their work. These biographies provide personal and scholarly views of America’s most distinguished researchers and a biographical history of U.S. science. Biographical Memoirs a re freely available online at www.nasonline.org/memoirs.
