A Depression childhood in the Bronx
Melvin Schwartz was born in New York City on November 2, 1932, at the depth of the Great Depression, and grew up in the Bronx in a Jewish family. His parents, he wrote, worked extraordinarily hard to give their children economic stability, and they gave him two qualities that became the foundation of his life: an unbounded sense of optimism, and a strong feeling that one’s mind should be used for the betterment of mankind.
His interest in physics began at twelve, when he entered the Bronx High School of Science, a public school for gifted students that would produce several Nobel laureates in physics. He remembered his four years there as among the most exciting of his life, chiefly because of the other students, who shared his background, interests and abilities. He later reflected on how much a young person’s direction depends on the company of peers.
Columbia in its golden age
In 1949 Schwartz entered Columbia University, which under I. I. Rabi had what he considered the finest physics department in the world; over the next thirteen years it would be home to six pieces of Nobel Prize work and many future laureates. He took his bachelor’s degree in 1953 and his doctorate in 1958, doing his thesis research at the Cosmotron accelerator at Brookhaven National Laboratory on Long Island, and he joined Columbia’s faculty in 1958, becoming a full professor in 1963.
He credited three colleagues with shaping his career: Jack Steinberger, his teacher and mentor, from whom he said he learned whatever taste and judgment he had in particle physics; the theorist T. D. Lee, who inspired his most famous experiment; and Leon Lederman, whom he called the sparkplug of American high-energy physics.
An idea after coffee
By 1959 physicists wanted to study the weak force, the force behind radioactive decay, at high energies, but it was hopelessly swamped by the strong and electromagnetic forces whenever energetic particles hit a target. Neutrinos feel only the weak force, but they interact so rarely that one could pass through a light year of lead without stopping. The only neutrinos physicists had detected came from nuclear reactors.
Late in 1959, Columbia’s physics department held one of its regular coffee hours, at which T. D. Lee led a discussion of possible experiments on weak interactions at high energies. One idea after another was rejected as impossible, and the meeting broke up in some frustration. That evening, Schwartz later recalled, the key notion came to him: perhaps the neutrinos produced when pions decay could be made in large enough numbers to be used as a beam. A quick calculation on the back of an envelope suggested it could be done at the new accelerators then being built. He telephoned Lee at home, and Lee’s enthusiasm was overwhelming. Planning began the next day. The Italian-Soviet physicist Bruno Pontecorvo, they soon learned, had reached similar ideas independently.
Two kinds of neutrino
Schwartz, Lederman, Steinberger and their colleagues Gordon Danby, Jean-Marc Gaillard, Konstantin Goulianos and Nariman Mistry built the experiment at Brookhaven’s new Alternating Gradient Synchrotron. Protons struck a beryllium target to make pions, which decayed in flight into muons and neutrinos. Everything except the neutrinos was then stopped by a wall of steel 13.5 metres thick, made from the deck plates of a dismantled navy cruiser. Behind it sat a ten-ton detector of a new kind, a spark chamber, made of aluminium plates in which a passing charged particle left a trail of sparks that could be photographed.
The question was whether the neutrinos that come from pion decay are the same as those from ordinary radioactive decay, which are associated with electrons. If they were the same, they should produce electrons and muons in equal numbers. In 1962 the team reported dozens of clean events in which a neutrino produced a muon, and only a handful of possible electron events. The neutrinos born alongside muons were a different particle, the muon neutrino.
The discovery showed that the lightest particles of matter, the leptons, come in families, each with its own neutrino. That pattern of families became a basic feature of the Standard Model of particle physics. Schwartz, Lederman and Steinberger shared the 1988 Nobel Prize in Physics for the neutrino beam method and for the discovery of the muon neutrino.
How the experiment was built
The experiment was a feat of patience as much as ingenuity. To keep out the cosmic rays that constantly rain down on any detector, the team switched the detector on only during the tiny fraction of each second when the accelerator’s beam was actually hitting the target, about two millionths of a second in every second, using a Cherenkov counter in front of the shielding wall to time the bursts. Counters covering the front, top and back of the spark chamber vetoed particles entering from outside. To avoid a flood of energetic muons, the accelerator was run at 15 billion electron volts rather than its full 30.
In the summer of 1960, T. D. Lee and C. N. Yang sharpened the purpose of the experiment by arguing that the absence of a certain muon decay could hardly be explained unless there were two kinds of neutrino. If they were right, the neutrinos from pion decay should produce muons and no electrons. Of the events found, 56 were clearly caused by neutrinos and contained muons, while only a handful of candidates looked like electrons. Running the experiment with the accelerator off, and checking that events pointed back toward the target through the steel, the team ruled out cosmic rays and neutrons as the cause.
A tool used ever since
Schwartz’s idea of making a beam of neutrinos at an accelerator, by colliding protons with a target and letting the resulting pions decay, became the standard way of studying neutrinos in the laboratory. Neutrino beams have been built at CERN, at Fermilab near Chicago and at J-PARC in Japan, and have fed experiments such as MINOS, NOvA, OPERA and T2K, which have measured how neutrinos change from one type to another as they travel, one of the most important discoveries in physics of recent decades.
As the New York Times put it, the 1962 experiment gave physicists a new way to study one of the fundamental forces of the universe.
Stanford, Silicon Valley and a return to physics
In 1966, after seventeen years at Columbia, Schwartz moved to Stanford University, where the new two-mile linear accelerator was nearly complete. There he studied an asymmetry in the decay of neutral kaons, a subtle difference between matter and antimatter, and succeeded in producing and detecting relativistic atoms made of a pion and a muon. In 1972 he published a textbook, Principles of Electrodynamics, that became a standard reference.
Increasingly frustrated by the growing size of physics collaborations, and lured by what he called the new industrial revolution in Silicon Valley, he founded Digital Pathways, Inc., in Mountain View in 1970. The company worked on the secure management of data communications, an early venture in computer security, and he eventually left Stanford to run it full-time. It was his company, not a university, that was listed as his affiliation when he received the Nobel Prize.
In 1991, encouraged by his old classmate Nicholas Samios, he returned to physics as Associate Director for High Energy and Nuclear Physics at Brookhaven, where colleagues said he was extremely influential in shaping the experimental programme of the Relativistic Heavy Ion Collider, built to recreate matter as it existed in the first moments of the universe. In 1994 he went back to Columbia as I. I. Rabi Professor of Physics, retiring in 2000.
Jewish roots and family
Schwartz grew up in the Jewish Bronx of the 1930s and 1940s, part of a generation of children of hard-working families who rose through New York’s free public schools and colleges into the front ranks of science. Wikipedia records that he was Jewish, and the Jewish Virtual Library lists him among Jewish Nobel laureates in physics. He did not write publicly about religious practice; what he chose to emphasise was the optimism and sense of duty his parents taught him.
He married Marilyn in the early 1950s and called her the most enduring thread of his life, without whose encouragement there would have been far less meaning to it. They had three children. Colleagues described him as a brilliant, unorthodox physicist who enjoyed every challenge and could be trusted to put the accepted scientific truths of the day to the test.
Last years and legacy
From 1997 Schwartz and his wife lived in Ketchum, Idaho. He suffered from Parkinson’s disease and hepatitis C, and he died at a nursing home in Twin Falls, Idaho, on August 28, 2006, at the age of 73.
His legacy is both an idea and a fact about nature. The idea, born after a coffee hour, was that the most elusive particles in the universe could be made into a beam and aimed at a detector; it opened the field of accelerator neutrino physics, which is still producing discoveries. The fact, that neutrinos come in more than one kind, helped reveal the family structure of matter on which the Standard Model is built. And in founding a computer security company in 1970, long before most people had heard of the problem, he showed the same optimistic willingness to try something new.
Sources & further reading
Melvin Schwartz, Biographical, NobelPrize.org · Melvin Schwartz, The First High Energy Neutrino Experiment, Nobel Lecture (PDF), NobelPrize.org · Nobel Laureate Melvin Schwartz Dies, August 28, Brookhaven National Laboratory · Melvin Schwartz, Wikipedia · Accelerator neutrino, Wikipedia · Melvin Schwartz, Jewish Virtual Library · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.