Val Logsdon Fitch

“My mother always told me that if you do anything worth praise, let others praise you, don’t praise yourself.” To friends of Val Logsdon Fitch, who died in Princeton, New Jersey, on 2 February 2015, that quotation from him says it all. Fortunately, he has left several eloquent recollections over the years, which we quote or paraphrase to capture the spirit of this great scientist and human being.Val Logsdon FitchPPT|High resolutionVal “was born on a cattle ranch not far from the South Dakota border on March 10, 1923 … just 20 years after the battle of Wounded Knee, which occurred about 40 miles northwest. The Sioux were very much a part of our environment, and my father, while not fluent, spoke their language. They recognized his friendly interest on their behalf by making him an honorary chief, naming him ‘Eagle Star.’ ” Soon after Val’s birth, the family moved to Gordon, Nebraska, where Val loved to work in his basement “laboratory,” which had a separate fuse box to prevent blackouts in the rest of the house. Graduating from Gordon High School in 1940 as valedictorian, he attended nearby Chadron State College until he was drafted into the US Army in March 1943.While in basic training, Val was selected for the army’s Specialized Training Program at the Carnegie Institute of Technology and then for the Manhattan Project. Given responsibilities far beyond his formal status, Val “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 … not just to consider using existing apparatus but to allow the mind to wander freely and invent new ways of doing the job.”.Under Ernest Titterton’s supervision, Val designed and built the apparatus to generate the signal that detonated the first atomic bomb on 16 July 1945. At the Trinity test he encountered a guard who had not been told what to expect: “He was absolutely pale and a look of incredible alarm was on his face. I simply said what was on my mind, ‘The war will soon be over.’ ”.After graduating from McGill University in electrical engineering, Val entered Columbia University in 1948. He worked with James Rainwater, who handed him a paper by John Wheeler on determining nuclear radii via x rays from captured muons and said it might make a good thesis topic. Val “took it and ran”; he built scintillation counters, trigger circuits, sodium iodide photon detectors, and a pioneering multichannel analyzer. “Every piece of electronics was home-designed and constructed. Nothing was available commercially.” The 1953 results were auspicious: Val and Rainwater found that nuclei were twice as dense as and far smaller than previously measured and showed that the muon had spin-½. They shared the front page of the New York Times with Edmund Hillary and his ascent of Mount Everest, and a pithy headline in the New York Daily News proclaimed, “A bad day for fission, the nucleus is just a shrimp.”.“Changing allegiance” to Princeton University in 1954, Val focused on the K mesons and first attacked the “τ – θ puzzle”: Two K-like particles had been found with the same mass but opposite parity, as evidenced by their decays τ+ → 3π and θ+ → 2π. Using the new Cosmotron at Brookhaven National Laboratory, Val found that the τ+ and θ+ lifetimes were equal within a few percent; that finding motivated T. D. Lee and C. N. Yang in their famous 1956 proposal that parity was not conserved—that the τ+ and θ+ are the same particle, the K+. Val’s key innovation, the velocity-selecting Cherenkov counter, cleanly separated K+ from protons and pions in the beam. Appropriately named the Fitch counter, it has been a workhorse ever since.Val next turned to the neutral kaons, coherent mixtures of K0 and its antiparticle K0¯. The mass eigenstates K1 = (K0 − K0¯)/2 and K2 = (K0 + K0¯)/2 were opposite eigenstates of charge conjugation–parity (CP), with different allowed decay modes and hence different lifetimes. In a kaon beam, the short-lived K1 component would quickly decay via K1 → 2π and leave a “pure” K2 beam in which 2π decays were forbidden by CP conservation. However, matter placed into a K2 beam preferentially absorbed the K0¯ component, “regenerating” short-lived K1s and hence 2π decays.In 1958 one of us (Cronin) joined Princeton and developed a spark-chamber spectrometer that had far better resolution than previous detectors. In spring 1963 Val suggested moving Cronin’s apparatus to the Alternating Gradient Synchrotron (AGS) at Brookhaven to pursue Robert Adair’s recent observation of large, “anomalous” K1 regeneration and search for K2 → π+π−. By July the experiment was running, and by Christmas postdoc René Turlay with student James Christenson had found 45 ± 10 K2 → π+π− candidate events. Efforts to find other explanations were unsuccessful, and the discovery published in the 27 July 1964 Physical Review Letters created a sensation.But to prove CP violation, Val went further and showed that the pions from the KL decay (neutral kaons were now called KL and KS) are coherent with those from KS decay, and in 1980 he and Cronin received the Nobel Prize. Val went on to exploit the interference between incident and coherently regenerated amplitudes to measure the KL – KS mass difference and invented the very precise “gap” method that became the standard in the field and a source of great pride.The CP discovery led Andrei Sakharov to pose a scenario that could explain the evolution from the Big Bang to a matter-dominated universe, a profound question unanswered to this day.Val left the study of kaons in 1972 and went first to Fermilab to search for C violation in proton–antiproton interactions, then to a cliff in Montana to search for short-distance gravitational forces, and back to the AGS to look for strange dibaryons. Though no signals were found, Val displayed his technical creativity and trained outstanding students.Val served on the President’s Science Advisory Committee in 1970–73, was chair of the Princeton physics department in 1976–81, and was president of the American Physical Society (APS) in 1987 and 1988, the only person since 1932 to serve two years. When an APS panel came under vicious personal attack for a report criticizing the Strategic Defense Initiative, Val rose to the defense, refuting the attackers’ technical claims and ad hominem diatribes. Val and the report were completely vindicated.Retirement in 1993 didn’t stop him: He led an AGS experiment searching for six-quark states, organized a major conference on Princeton’s 250th anniversary, and wrote historical articles on particle physics. We shall never forget Val Fitch, who was by any measure a most exceptional scientist and human being.© 2015 American Institute of Physics.

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