Jack Steinberger (born Hans Jakob Steinberger; May 25, 1921 – December 12, 2020) was a German-born American physicist noted for his work with neutrinos, the subatomic particles considered to be elementary constituents of matter. He was a recipient of the 1988 Nobel Prize in Physics, along with Leon M. Lederman and Melvin Schwartz, for the discovery of the muon neutrino. Through his career as an experimental particle physicist, he held positions at the University of California, Berkeley, Columbia University (1950–68), and the CERN (1968–86). He was also a recipient of the United States National Medal of Science in 1988, and the Matteucci Medal from the Italian Academy of Sciences in 1990.
Early life and education Steinberger was born in the city of Bad Kissingen in Bavaria, Germany, on May 25, 1921, into a Jewish family. The rise of Nazism in Germany, with its open anti-Semitism, prompted his parents, Ludwig Lazarus (a cantor and religious teacher) and Berta May Steinberger, to send him out of the country. Steinberger emigrated to the United States at the age of 13, making the trans-Atlantic trip with his brother Herbert. Jewish charities in the U.S. arranged for Barnett Farroll to care for him as a foster child. Steinberger attended New Trier Township High School, in Winnetka, Illinois. He was reunited with his parents and younger brother in 1938. Steinberger studied chemical engineering at Armour Institute of Technology (now Illinois Institute of Technology) but left after his scholarship ended to help supplement his family's income. He obtained a bachelor's degree in chemistry from the University of Chicago, in 1942. Shortly thereafter, he joined the Signal Corps at MIT. With the help of the G.I. Bill, he returned to graduate studies at the University of Chicago in 1946, where he studied under Edward Teller and Enrico Fermi. His Ph.D. thesis concerned the energy spectrum of electrons emitted in muon decay; his results showed that this was a three-body decay, and implied the participation of two neutral particles in the decay (later identified as the electron ( ν e {\displaystyle \nu _{e}} ) and muon ( ν μ {\displaystyle \nu _{\mu }} ) neutrinos) rather than one.
Career
Early research After receiving his doctorate, Steinberger attended the Institute for Advanced Study in Princeton for a year. In 1949 he published a calculation of the lifetime of the neutral pion, which anticipated the study of anomalies in quantum field theory. Following Princeton, in 1949, Steinberger went to the Radiation Lab at the University of California at Berkeley, where he performed an experiment which demonstrated the production of neutral pions and their decay to photon pairs. This experiment utilized the 330 MeV synchrotron and the newly invented scintillation counters. Despite this and other achievements, he was asked to leave the Radiation Lab at Berkeley in 1950, due to his refusal to sign the so-called non-Communist Oath. Steinberger accepted a faculty position at Columbia University in 1950. The newly commissioned meson beam at Nevis Labs provided the tool for several important experiments. Measurements of the production cross-section of pions on various nuclear targets showed that the pion has odd parity. A direct measurement of the production of pions on a liquid hydrogen target, then not a common tool, provided the data needed to show that the pion has spin zero. The same target was used to observe the relatively rare decay of neutral pions to a photon, an electron, and a positron. A related experiment measured the mass difference between the charged and neutral pions based on the angular correlation between the neutral pions produced when the negative pion is captured by the proton in the hydrogen nucleus. Other important experiments studied the angular correlation between electron–positron pairs in neutral pion decays, and established the rare decay of a charged pion to an electron and neutrino; the latter required use of a liquid-hydrogen bubble chamber.
Investigations of strange particles During 1954–1955, Steinberger contributed to the development of the bubble chamber with the construction of a 15 cm device for use with the Cosmotron at Brookhaven National Laboratory. The experiment used a pion beam to produce pairs of hadrons with strange quarks to elucidate the puzzling production and decay properties of these particles. In 1956, he used a 30 cm chamber outfitted with three cameras to discover the neutral Sigma hyperon and measure its mass. This observation was important for confirming the existence of the SU(3) flavor symmetry which hypothesizes the existence of the strange quark. An important characteristic of the weak interaction is its violation of parity symmetry. This characteristic was established through the measurement of the spins and parities of many hyperons. Steinberger and his collaborators contributed several such measurements using large (75 cm) liquid-hydrogen bubble chambers and separated hadron beams at Brookhaven. One example is the measurement of the invariant mass distribution of electron–positron pairs produced in the decay of Sigma-zero hyperons to Lambda-zero hyperons.
Neutrinos and the weak neutral current In the 1960s, the emphasis in the study of the weak interaction shifted from strange particles to neutrinos. Leon Lederman, Steinberger and Schwartz built large spark chambers at Nevis Labs and exposed them in 1961 to neutrinos produced in association with muons in the decays of charged pions and kaons. They used the Alternating Gradient Synchrotron (AGS) at Brookhaven, and obtained a number of convincing events in which muons were produced, but no electrons. This result, for which they received the Nobel Prize in 1988, proved the existence of a type of neutrino associated with the muon, distinct from the neutrino produced in beta decay.
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