Jack Steinberger obituary | Particle physics

Jack Steinberger, who died at the age of 99, was one of three winners of the Nobel Prize in Physics in 1988 for his work on neutrinos and the discovery of the muon neutrino. This research has done much to advance the understanding of fundamental particles.

The reality of the ghostly neutrino was not confirmed experimentally until 1956, but in 1948, working at the University of Chicago, Steinberger had first given indirect clues to its presence in his measurement of muon decays – a sibling electron heavy. He showed that when a muon turns into an electron, two very light, possibly massless, electrically neutral particles are also produced. These, it was later shown, are neutrinos.

With his demonstration that the muon did not decay by the more direct route of photon radiation, Steinberger had also unwittingly given the first hint that a muon is not simply a heavy version of the electron, but has a some intrinsic “muon flavor”. The nature of this “flavor” remains a mystery, but it has become a staple of modern particle physics theory.

Soon, theorists suspected that the two neutrinos produced during muon decay could not be identical. The idea has emerged that there are two flavors of neutrino: the ‘neutrino-electron’ having an affinity for the electron, and its sibling the ‘neutrino-muon’, paired analogously to the muon. Experimental proof of this fundamental key to the fundamental particle model came in 1962 thanks to Steinberger and his colleagues Melvin Schwartz and Leon Lederman.

At Brookhaven National Laboratory on Long Island, New York, the trio developed techniques to produce intense beams of high-energy neutrinos. At high energies, the probability of neutrinos interacting with material targets increases to a level that makes them experimentally viable. Their breakthrough inspired decades of experimental work involving neutrinos, and their first experiment with high-energy neutrinos confirmed the distinct identities of the electron neutrino and the muon neutrino.

Essentially, there were two ways to produce neutrinos, one where they emerge in association with a muon, another where they arrive with an electron. According to the theory, the former are muon neutrinos, the latter electron neutrinos. What Steinberger and his colleagues discovered was that when beams of the first variety – muon neutrinos – hit targets and picked up an electric charge, the charge was invariably carried by a muon, whereas in the other case , the charge was carried by an electron.

This confirmed that neutrinos carry a memory of their birth, metaphorical DNA that is passed on to offspring in subsequent interactions. This DNA analog is known as “flavor” and has become a key property in the modern standard model of fundamental particles.

He was born Hans Jakob Steinberger in Bad Kissingen, a Bavarian spa town in Germany, son of May and Ludwig Steinberger. Her father, a teacher in the town’s small Jewish community, had been a veteran of the German army in World War I, but with the rise of the Nazis, the Steinberger family had no future in their country. In 1934, Hans and his older brother headed to the United States, sponsored by an American organization that had volunteered to bring 300 Jewish children to the country. The rest of the family joins them a year later.

His parents went on to run a delicatessen in Winnetka, Illinois, where Jack – as he was known after arriving in the United States – attended New Trier High School and what was then the Armor Institute of Technology of Chicago, before entering the University of Chicago. There he earned a degree in chemistry and made a calculation of the lifetime of the electrically neutral pi meson, which later played an important role in the development of theoretical particle physics. Nevertheless, Steinberger felt he was not good enough to shine in theory and instead focused on experiments. During World War II, he worked on radar development in the radiation laboratory at the Massachusetts Institute of Technology, before returning to Chicago to study physics under Enrico Fermi, earning his doctorate in 1948.

He then went to the University of California, Berkeley for a year but left because, although not a communist, he refused on principle to sign a loyalty oath attesting to the fact. He moved to Columbia University, New York, joining the faculty in 1950 and eventually becoming a full professor there. He left Columbia to take up a position at the European Center for Particle Physics, CERN, in Geneva, in 1968.

Jack Steinberger, left, in conversation with fellow physicist Lev Landau of the Soviet Union, right, at a science conference on high-energy particles in 1956. Photography: Sovfoto/Universal Images Group/Rex/Shutterstock

In 1988, Steinberger was one of the main instigators of the Aleph collaboration of more than 300 physicists working at CERN’s electron-positron collider, LEP, then under construction. LEP was specifically designed to produce the massive Z boson, which is a key agent of the weak nuclear force and is also a gateway to the study of neutrinos. Precision measurements of the properties of the Z boson have proven that there are not two but three – and no more than three – varieties of light neutrinos. In doing so, particle physics established a modern analogue of Dmitri Mendeleev’s periodic table of elements, the cornerstone of which, the Higgs boson, was discovered in 2012.

Steinberger never forgot his welcome to the United States as a refugee. He donated his Nobel Prize medal to his former school, noting that his “good start was one of the many important privileges of my life”.

He remained active in research and was regularly present at CERN conferences until he was 90 years old.

His first marriage, to Joan Beauregard, ended in divorce, after which he married Cynthia Alff, a biologist. He is survived by his four children, two from each marriage.

Jack Steinberger, physicist, born May 25, 1921; passed away on December 12, 2020

This article was updated on January 22, 2021 to correct details of Jack Steinberger’s early years.

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