CPH Theory

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به نشریه الکترونیکی سی. پی. اچ.

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Nobel 1980

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CP Symmetry Violation – The Search for Its Origin

The Discovery of Charge – Conjugation Parity Asymmetry

"for the discovery of violations of fundamental symmetry principles in the decay of neutral K-mesons"

James Watson Cronin	Val Logsdon Fitch

1/2 of the prize	1/2 of the prize
USA	USA
University of Chicago Chicago, IL, USA	Princeton University Princeton, NJ, USA
b. 1931	b. 1923

Autobiography: James Watson Cronin

I was born on September 29, 1931 in Chicago, Illinois, while my father, James Farley Cronin, was a graduate student at the University of Chicago. He was a student of classical languages. My mother, Dorothy Watson, had met my father in a Greek class at Northwestern University. After a brief stay at a small school in Alabama, my father became Professor of Latin and Greek at Southern Methodist University in Dallas, Texas, in September 1939. My primary and secondary education was provided by the Highland Park Public School System. I received my undergraduate degree from Southern Methodist University with a major in physics and mathematics in 1951. In high school my natural interest in science was encouraged by an excellent physics teacher, Mr. Charles H. Marshall. He stressed analytical methods as applied to simple physical systems as well as practical experimental problems.

My real education began when I entered the University of Chicago in September 1951 as a graduate student. I was fortunate to have among my classroom teachers, Enrico Fermi, Maria Mayer, Edward Teller, Gregor Wentzel, Val Telegdi, Marvin Goldberger and Murray Gell-Mann. I did a thesis in experimental nuclear physics under the direction of Samuel K. Allison. While at Chicago my interest in the new field of particle physics was stimulated by a course given by Gell- Mann, who was developing his ideas about Strangeness at the time.

It was also at the University of Chicago that I met my future wife, Annette Martin, in the summer of 1953. It was a wonderful, happy summer; I had passed my Ph.D. qualifying exams the previous winter, and I realized that I had met my lifetime companion. We were married in September 1954. The stable point in my life became our home. On even the worst days, when nothing was working at the lab, I knew that at home I would find warmth, peace, companionship, and encouragement. As a consequence, the next day would surely be better. Annette, with great patience and good spirit, tolerated my many long absences when experiments were carried out at distant laboratories.

After receiving my Ph.D. in 1955 I had the opportunity to join the group of Rodney Cool and Oreste Piccioni who were working at the Brookhaven Cosmotron, a newly completed 3 GeV accelerator. That period was an exciting time in physics. The famous tau-teta puzzle led to the prediction of parity violation and the experimental demonstration of its violation. The long-lived K meson was discovered at Brookhaven.

When the violation of parity was discovered I began a series of electronic experiments to investigate parity violation in hyperon decays. In early 1958 the Cosmotron suffered a severe magnet failure. As a consequence, we moved our experiment to the Berkeley Bevatron. Here I had the good fortune to meet William Wenzel and Bruce Cork. These physicists had a great influence on me. From their example I learned not to be intimidated by complex pieces of apparatus.

While at Brookhaven I met Val Fitch who was responsible for my coming to Princeton University in the fall of 1958. At Princeton all the work in particle physics was supported through a contract with the Office of Naval Research. The Director of the Laboratory, George Reynolds, was most supportive of my efforts to work independently. There followed for ten years a glorious time for research. I was much involved in the development of the spark chamber as a practical research tool. During this period, with a series of excellent students, we further studied hyperon decays. Then we joined with Val Fitch to study neutral K meson decays which led to the discovery of CP violation.

Following the discovery in the summer of 1964, I spent a year in France working at the Centre d'Etudes Nucleaires at Saclay with Rene Turlay. In addition to the research, I enjoyed learning French and assimilating the culture of another country. One of the greatest joys in my life was giving a lecture in French at the College de France.

On returning to Princeton in 1965, I began with students a series of experiments to study the neutral CP violating decay modes of the long lived neutral K meson. These experiments lasted until 1971. In 1971 I returned to the University of Chicago as Professor of Physics. The fact that the new Fermilab 400 GeV Accelerator was being built near Chicago made this move an attractive one. At Fermilab, with younger associates and students, I carried out experiments on the production of particles at high transverse momentum, and on the production of direct leptons. At present with my colleague at Chicago, Bruce Winstein, I am preparing to study with much greater accuracy some of the CP violating parameters of the neutral K meson.

I now live in Chicago near the campus with my wife Annette, and son Daniel. My oldest daughter Cathryn lives and works in New York City. My daughter Emily attends the University of Minnesota. My mother remained in Dallas, Texas, after the death of my father in 1959. For recreation we have a cabin in the woods in Wisconsin which we visit year-round. In the summer we spend some time in Aspen, Colorado. Our whole family assembles in Chicago at Christmas and usually in Aspen in the summer.

Education

B.S., Southern Methodist University, 1951

M.S., University of Chicago, 1953

Ph.D., (Physics) University of Chicago, 1955

Career

National Science Foundation Fellow, 1952-1955

Assistant Physicist, Brookhaven National Laboratory, 1955-1958

Assistant Professor of Physics, Princeton University, 1958-1962

Associate Professor of Physics, Princeton University, 1962-1964

Professor of Physics, Princeton University, 1964-1971

University Professor of Physics, University of Chicago, 1971-

Member

American Academy of Arts and Sciences

American Physical Society

National Academy of Sciences

Recipient

Research Corporation Award, 1968

John Price Wetherill Medal of the Franklin Institute, 1975

Ernest O. Lawrence Award, 1977

Autobiography: Val Logsdon Fitch

I was born the youngest of three children, on a cattle ranch in Cherry County, Nebraska, not far from the South Dakota border, on March 10, 1923. This is a very sparsely populated part of the United States and remote from any center of population. It seems incredible by modern standards that by the age of 20 my father, Fred Fitch, had acquired a ranch of more than 4 square miles and had persuaded a local school teacher, Frances Logsdon, to marry and join him in living there. They moved to the ranch just 20 years after the battle of Wounded Knee, which occurred about 40 miles northwest. I mention this because our living close to their reservation made the Sioux Indians very much a part of our environment. My father, while not fluent, spoke their language. They recognized his friendly interest on their behalf by making him an honorary chief.

Not long after my birth my father was badly injured when a horse he was riding fell with him. He subsequently had to give up the physically strenuous activity associated with running a ranch and raising cattle. The family moved to Gordon, Nebraska, a town about 25 miles away, where my father entered the insurance business. All of my formal schooling through high school was in the public schools of Gordon. During this period my parents retained ownership of the ranch but the operation was largely left to others. E.B. White has defined farming as 10% agriculture and 90% fixing something that has gotten broken. My memories of ranching are primarily not the romantic ones of rounding up and branding cattle but rather of oiling windmills and fixing fences.

Probably the most significant occurrence in my education came when, as a soldier in the U.S. Army in WWII, I was sent to Los Alamos, New Mexico, to work on the Manhattan Project. The work I did there under the direction of Ernest Titterton, a member of the British Mission, was highly stimulating. The laboratory was small and even as a technician garbed in a military fatigue uniform I had the opportunity to meet and see at work many of the great figures in physics: Fermi, Bohr, Chadwick, Rabi, Tolman. I have recorded some of the experiences from those days in a chapter in All in Our Time, a book edited by Jane Wilson and published by the Bulletin of Atomic Scientists. I spent 3 years at Los Alamos and in that period learned well the techniques of experimental physics. I observed that the most accomplished experimentalists were also the ones who knew most about electronics and electronic techniques were the first I learned. But mainly I learned, in approaching the measurement of new phenomena, not just to consider using existing apparatus but to allow the mind to wander freely and invent new ways of doing the job.

Robert Bacher, the leader of the physics division in which I worked, offered me a graduate assistantship at Cornell after the war but I still had to finish the work for an undergraduate degree. This I did at McGill University. And then another opportunity for graduate work came from Columbia and I ended up there working with Jim Rainwater for my Ph.D. thesis. One day in his of fice, which he shared at the time with Aage Bohr, he handed me a preprint of a paper by John Wheeler devoted to µ-mesic atoms. This paper emphasized, in the case of the heavier nuclei, the extreme sensitivity of the Is level to the size of the nucleus. Even though the radiation from these atoms had never been observed, these atomic systems might be a good thesis topic. At this same time a convergence of technical developments took place. The Columbia Nevis cyclotron was just coming into operation. The beams of (pi)-measons from the cyclotron contained an admixture of µ-measons which came frome the decay of the (pi)'s and which could be separated by range. Sodium iodide with thallium activation had just been shown by Hofstadter to be an excellent scintillation counter and energy spectrometer for gamma rays. And there were new phototubes just being produced by RCA which were suitable matches to sodium iodide crystals to convert the scintillations to electrical signals. The other essential ingredient to make a gamma-ray spectrometer was a multichannel pulse height analyzer which, utilizing my Los Alamos experience, I designed and built with the aid of a technician. The net result of all the effort for my thesis was the pioneering work on µ-mesic atoms. It is of interest to note that we came very close to missing the observation of the gamma-rays completely. Wheeler had calculated the 2p-1s transition energy in Pb, using the then accepted nuclear radius 1.4 A^1/3 fermi, to be around 4.5 MeV. Correspondingly, we had set our spectrometer to look in that energy region. After several frustrating days, Rainwater suggested we broaden the range and then the peak appeared - not at 4.5 MeV but at 6 MeV! The nucleus was substantially smaller than had been deduced from other effects. Shortly afterwards Hofstadter got the same results from his electron scattering experiments. While the µ-mesic atom measurements give the rms radius of the nucleus with extreme accuracy the electron scattering results have the advantage of yielding many moments to the charge distribution. Now the best information is obtained by combining the results from both µ-mesic atoms and electron scattering.

Subsequently, in making precise gamma-ray measurements to obtain a better mass value for the µ-meson, we found that substantial corrections for the vacuum polarization were required to get agreement with independent mass determinations. While the vacuum polarization is about 2% of the Lamb shift in hydrogen it is the very dominant electrodynamic correction in µ-mesic atoms.

My interest then shifted to the strange particles and K mesons but I had learned from my work at Columbia the delights of unexpected results and the challenge they present in understanding nature. I took a position at Princeton where, most often working with a few graduate students, I spent the next 20 years studying K-mesons. The ultimate in unexpected results was that which was recognized by the Nobel Foundation in 1980, the discovery of CP-violation.

At any one time there is a natural tendency among physicists to believe that we already know the essential ingredients of a comprehensive theory. But each time a new frontier of observation is broached we inevitably discover new phenomena which force us to modify substantially our previous conceptions. I believe this process to be unending, that the delights and challenges of unexpected discovery will continue always.

It is highly improbable, a priori, to begin life on a cattle ranch and then appear in Stockholm to receive the Nobel Prize in physics. But it is much less improbable to me when I reflect on the good fortune I have had in the ambiance provided by my parents, my family, my teachers, colleagues and students. I have two sons from my marriage to Elise Cunningham who died in 1972. In 1976 I married Daisy Harper who brought with her three stepchildren into my life.

Honors and Distinctions
I am a fellow of the American Physical Society and the American Association for the Advancement of Science, a member of the American Academy of Arts and Sciences and the National Academy of Sciences. I hold the Cyrus Fogg Brackett Professorship of Physics at Princeton University and since 1976 have served as chairman of the Physics Department. I received the E. O. Lawrence award in 1968. In 1967 Jim Cronin and I received the Research Corporation award for our work on CP violation and in 1976 the John Price Witherill medal of the Franklin Institute.

Nobel Lecture: James Watson Cronin