I was born in Bad Kissingen (Franconia) in 1921. At that time my father, Ludwig, was 45 years old. He was one of twelve children of a rural ‘Viehhändler’ (small-time cattle dealer). Since the age of eighteen he had been cantor and religious teacher for the little Jewish community, a job he still held when he emigrated in 1938. He had been a bachelor until he returned from four years of service in the German Army in the first World War. My mother was born in Nuremberg to a hop merchant, and was fifteen years the younger. Unusual for her time, she had the benefit of a college education and supplemented the meagre income with English and French lessons, mostly to the tourists which provided the economy of the spa. The childhood I shared with my two brothers was simple; Germany was living through the post-war depression.
Things took a dramatic turn when I was entering my teens. I remember Nazi election propaganda posters showing a hateful Jewish face with crooked nose, and the inscription “Die Juden sind unser Ungluck”, as well as torchlight parades of SA storm troops singing “Wenn’s Juden Blut vom Messer fliesst, dann geht’s noch mal so gut”. In 1933, the Nazis came to power and the more systematic persecution of the Jews followed quickly. Laws were enacted which excluded Jewish children from higher education in public schools. When, in 1934, the American Jewish charities offered to find homes for 300 German refugee children, my father applied for my older brother and myself. We were on the SS Washington, bound for New York, Christmas 1934.
I owe the deepest gratitude to Barnett Faroll, the owner of a grain brokerage house on the Chicago Board of Trade, who took me into his house, parented my high-school education, and made it possible also for my parents and younger brother to come in 1938 and so to escape the holocaust. New Trier Township High School on the well-to-do Chicago North Shore, enjoyed a national reputation, and, with a swimming pool, athletic fields, cafeteria, as well as excellent teachers, offered horizons unimaginable to the young emigrant from a small German town.
The reunited family settled down in Chicago. We were helped to acquire a small delicatessen store which was the basis of a very marginal income, but we were used to a simple life, so this was no problem. I was able to continue my education for two years at the Armour Institute of Technology (now the Illinois Institute of Technology) where I studied chemical engineering. I was a good student, but these were the hard times of the depression, my scholarship came to an end, and it was necessary to work to supplement the family income.
The experience of trying to find a job as a twenty-year-old boy without connections was the most depressing I was ever to face. I tried to find any job in a chemical laboratory: I would present myself, fill out forms, and have the door closed hopelessly behind me. Finally through a benefactor of my older brother, I was accepted to wash chemical apparatus in a pharmaceutical laboratory, G.D. Searl and Co., at eighteen dollars a week. In the evenings I studied chemistry at the University of Chicago, the weekends I helped in the family store.
The next year, with the help of a scholarship from the University of Chicago, I could again attend day classes, so that in 1942 I could finish an undergraduate degree in chemistry.
On 7 December 1941, Japan attacked the United States at Pearl Harbor. I joined the Army and was sent to the MIT radiation laboratory after a few months of introduction to electromagnetic wave theory in a special course, given for Army personnel at the University of Chicago. My only previous contact with physics had been the sophomore introductory course at Armour. The radiation laboratory was engaged in the development of radar bomb sights; I was assigned to the antenna group. Among the outstanding physicists in the laboratory were Ed Purcell and Julian Schwinger. The two years there offered me the opportunity to take some basic courses in physics.
After Germany surrendered in 1945, I spent some months on active duty in the Army, but was released after the Japanese surrender, to continue my studies at the University of Chicago. It was a wonderful atmosphere, both between professors and students and also among the students. The professors to whom I owe the greatest gratitude are Enrico Fermi, W. Zachariasen, Edward Teller and Gregor Wentzel. The courses of Fermi were gems of simplicity and clarity and he made a great effort to help us become good physicists also outside the regular class-room work, by arranging evening discussions on a widespread series of topics, where he also showed us how to solve problems. Fellow students included Yang, Lee, Goldberger, Rosenbluth, Garwin, Chamberlain, Wolfenstein and Chew. There was a marvellous collaboration, and I feel I learned as much from these fellow students as from the professors.
I would have preferred to do a theoretical thesis, but nothing within reach of my capabilities seemed to offer itself. Fermi then asked me to look into a problem raised in an experiment by Rossi and Sands on stopping cosmic-ray muons. They did not find the expected number of decays. After correcting for geometrical losses there was still a missing factor of two, and I suggested to Sands that this might be due to the fact that the decay electron had less energy than expected in the two-body decay, and that one might test this experimentally. When this idea was not followed, Fermi suggested that I do the experiment, instead of waiting for a theoretical topic to surface. The cosmic-ray experiment required less than a year from its conception to its conclusion, in the end of the summer of 1948. It showed that the muon’s is a three-body decay, probably into an electron and two neutrinos, and helped lay the experimental foundation for the concept of a universal weak interaction.
There followed an interlude to try theory again at the Institute for Advanced Study in Princeton, where Oppenheimer had become director. It was a frustrating year: I was no match for Dyson and other young theoreticians assembled there. Towards the end I managed to find a piece of work I could do, on the decay of mesons via intermediate nucleons. I still remember how happy Oppenheimer was to see me come up with something, at last.
In 1949, Gian Carlo Wick, with whom I had done some work on the scattering of polarized neutrons in magnetized iron while still a graduate student at Chicago University, invited me to be his assistant at the University of California in Berkeley. There the experimental possibilities in the Radiation Laboratory, created by E.O. Lawrence, were so great that I reverted easily to my wild state, that is experimentation. During the year there, I had the magnificent opportunity of working on the just completed electron synchrotron of Ed McMillan. It enabled me to do the first experiments on the photoproduction of pions (with A.S. Bishop) to establish the existence of neutral pions (with W.K.H. Panofsky and J. Stellar) as well as to measure the pion mean life (with O. Chamberlain, R.F. Mozley and C. Weigand).
I survived only a year in Berkeley, partly because I declined to sign the anticommunist loyalty oath, and moved on to Columbia University in the summer of 1950. At its Nevis Laboratory, Columbia had just completed a 380 MeV cyclotron; this, for the first time, offered the possibility of experimenting with beams of T mesons. In the next years I exploited these beams to determine the spins and parities of charged and neutral pions, to measure the pi– pi0 mass difference and to study the scattering of charged pions. This work leaned heavily on the collaboration of Profs. D. Bodansky and A.M. Sachs, as well as of several Ph.D. students: R. Durbin, H. Loar, P. Lindenfeld, W. Chinowsky and S. Lokanathan.
These experiments all utilized small scintillator counters. In the early fifties, the bubble-chamber technique was discovered by Don Glaser, and in 1954 three graduate students, J. Leitner, N.P. Samios and M. Schwartz, and myself began to study this technique which had not as yet been exploited to do physics. Our first effort was a 10 cm diameter propane chamber. We made one substantial contribution to the technique, that was the realization of a fast recompression (within ~10 ms), so that the bubbles were recompressed before they could grow large and move to the top. This permitted chamber operation at a useful cycling rate. The first bubble-chamber paper to be published was from our experiment at the newly built Brookhaven Cosmotron, using a 15 cm propane chamber without magnetic field. It yielded a number of results on the properties of the new unstable (strange) particles at a previously unattainable level, and so dramatically demonstrated the power of the new technique which was to dominate particle physics for the next dozen years. Only a few months later we published our findings on three events of the type Sigma0-> Delta0 + gamma, which demonstrated the existence of the Sigma0 hyperon and gave a measure of its mass. This experiment used a new propane chamber, eight times larger in volume, and with a magnetic field. This chamber also introduced the use of more than two stereo cameras, a development which is crucial for the rapid, computerized analysis of events, and has been incorporated into all subsequent bubble chambers.
In the decade which followed, the same collaborators, together with Profs. Plano, Baltay, Franzini, Colley and Prodell, and a number of new students, constructed three more bubble chambers: a 12″ H2 chamber as well as 30″ propane and H2 chambers, developed the analysis techniques, and performed a series of experiments to clarify the properties of the new particles. The experiments I remember with the most pleasure are:
– the demonstration of parity violation in D decay, 1957;
– the demonstration of the ß decay of the pion, 1958;
– the determination of the p0 parity on the basis of angular correlation in the double internal conversion of the g rays, 1962;
– the determination of the w and j decay widths (lifetimes), 1962;
– the determination of the S0 – D0 relative parity, 1963;
– the demonstration of the validity of the DS = DQ rule in K0 and in hyperon decays, 1964.
This long chain of bubble-chamber experiments, in which I also enjoyed and appreciated the collaboration of two Italian groups, the Bologna group of G. Puppi and the Pisa group of M. Conversi, was interrupted in 1961, in order to perform, at the suggestion of Mel Schwartz, and with G. Danby, J.M. Gaillard, D. Goulianos, L. Lederman and N. Mistri, the first experiment using a high-energy neutrino beam now recognized by the Nobel Prize, and described in the paper of M. Schwartz.
In 1964, CP violation was discovered by Christensen, Cronin, Fitch and Turlay. Soon after I found myself on sabbatical leave at CERN, and proposed, together with Rubbia and others, to look for the interference between K0s and K0L amplitudes in the time dependence of K0 decay. Such interference was expected in the CP violation explanation of the results of Christensen et al., but not in other explanations which had also been proposed. The experiment was successful, and marked the beginning of a set of experiments to learn more about CP violation, which was to last a decade. The next result was the observation of the small, CP-violating, charge asymmetry in K0L leptonic decay, in 1966. Measurement of the time dependence of this charge asymmetry, following a regenerator, permitted a determination of the regeneration phase; this, together with the earlier interference experiments, yielded, for the first time, the CP-violating phase jh+ – and, in consequence, as well as the observed magnitudes of the CP-violating amplitudes in the two-pion and the leptonic decays, certain checks of the superweak model. The same experiment also gave a more sensitive check of the DS = DQ rule, an ingredient of the present Standard Model.
In 1968, I joined CERN. Charpak had just invented proportional wire chambers, and this development offered a much more powerful way to study the K0 decay to which I had become addicted. Two identical detectors were constructed, one at CERN together with Filthuth, Kleinknecht, Wahl, and others, and one at Columbia together with Christensen, Nygren, Carithers and students. The Columbia beam was long, and therefore contained no Ks but only KL, the CERN beam was short, and therefore contained a mixture of Ks and KL. It was contaminated by a large flux of L0, and so was also a hyperon beam, permitting the first measurements of L0 cross-sections as well as the Coulomb excitation of L0 to S0, a difficult and interesting experiment carried out chicfly by Steffen and Dydak. The most important result to come from the Columbia experiment was the observation of the rare decay KL -> µ+µ– with a branching ratio compatible with theoretical predictions based on unitarity. Previously, a Berkeley experiment had searched in vain for this decay and had claimed an upper limit in violation of unitarity. Since unitarity is fundamental to field theory, this result had a certain importance.
The CERN experiment, which extended until 1976, produced a series of precise measurements on the interference of Ks and KL in the two-pion and leptonic decay modes, thus leading us to obtain highly precise results on the CP-violating parameters in K0 decay. I believe the experiment was beautiful, and take some pride in it, but the results were all in agreement with the superweak model and so did little towards understanding the origin of CP violation.
In 1972, the K0 collaboration of CERN, Dortmund and Heidelberg was joined by a group from Saclay, under R. Turlay, to study the possibilities for a neutrino experiment at the CERN SPS then under construction. The CDHS detector, a modular array of magnetized iron disks, scintillation counters and drift chambers, 3.75 m in diameter, 20 m long, and weighing 1200 t, was designed, constructed, and exposed to different neutrino beams at the SPS during the period 1977 to 1983. It provided a large body of data on the charged-current and neutral-current inclusive reactions in iron, which permitted first of all the clearing away of a number of incorrect results, e.g. the “high-y anomaly” produced at Fermilab, allowed the first precise and correct determination of the Weinberg angle, demonstrated the existence of right-handed neutral currents, provided measurements of the structure functions which gave quantitative support to the quark constituent model of the nucleon, and, through the Q2 evolution of the structure functions, gave quantitative support to QCD. The study of multimuon events gave quantitative support to the GIM model of the Cabibbo current through its predictions on charm production.
In the CDHS experiment we were about thirty physicists. Since 1983, I have been spokesman for a collaboration of 400 physicists engaged in the design and construction of a detector for the 100 + 100 GeV e+e– Collider, LEP, to be ready at CERN in the beginning of 1989. In the meantime I had also helped to design an experiment to compare CP violation in the charged and neutral two-pion decay of the K0L. This experiment was the first to show “direct” CP violation, an important step towards the understanding of CP violation.
In 1986, I retired from CERN and became part-time Professor at the Scuola Normale Superiore in Pisa. However, my chief activity continues as before in my research at CERN.
I am married to Cynthia Alff, my former student and now biologist, and we have two marvellous children, Julia, 14 years old, and John, 11 years old. From an earlier marriage to Joan Beauregard, there are two fine sons, Joseph Ludwig and Richard Ned.
I play the flute, unfortunately not very well, and have enjoyed tennis, mountaineering and sailing, passionately.
This autobiography/biography was written at the time of the award and first published in the book series Les Prix Nobel. It was later edited and republished in Nobel Lectures. To cite this document, always state the source as shown above.
Addendum, June 2005
In 1988, I was the spokesman of a collaboration of about 350 physicists, preparing the detector we called ALEPH, which we had started to plan in 1981, for the CERN electron-positron collider then under construction called LEP, and which started to operate in 1989. Altogether, about fifteen hundred physicists participated, using four such detectors. LEP results dominated CERN physics, perhaps the world’s, for a dozen or more years, with crucial, precise measurements, which confirmed the Standard Model of the unified electro-weak and strong interactions. The physics scene had changed a lot since the time of my thesis experiment in 1948, which I could do quite alone. For some time I could help, as manager, but also contributing to the detector design and the physics analysis. This came to an end in 1995, partly because I had no new ideas on the physics we might learn, and partly because the challenges became more and more technical, especially in the use of computers, and I could not compete with the younger generation.
Since that time I have enjoyed learning cosmology and astrophysics, and following its progress. This has given me much satisfaction: on the one hand it involved having to learn some basic physics new to me, physics important to cosmology but unimportant in particle physics, such as general relativity and hydrodynamics, on the other hand these have been spectacular years in astrophysics, with the discovery in 1992, and continually improving observational results, of the inhomogeneities of the cosmic microwave background radiation, which give a totally new map of the universe, at a much earlier time than stars or galaxies, much simpler and therefore much easier to learn from, and more precisely. I still come to CERN, the 10 km on my bicycle, every day and sometimes enjoy trying to learn something new.Copyright © The Nobel Foundation 2005