Melvin Schwartz thought up the neutrino beam

Person: Melvin Schwartz
Lived: 1932–2006
Field: Particle physics
From: American

The story

Melvin Schwartz was born in New York in 1932 and grew up in a Jewish family in the Bronx during the Great Depression. His parents, he wrote, gave him optimism and a strong feeling that one’s mind should be used for the betterment of mankind. He studied at the Bronx High School of Science and at Columbia University, where he joined the faculty in 1958.

In 1959 physicists wanted to study the weak force at high energies, but whenever energetic particles struck a target the weak effects were swamped by the strong and electromagnetic forces. Neutrinos feel only the weak force, but they interact so rarely that one can pass through a light year of lead. Late that year, at a Columbia coffee hour, T. D. Lee led a discussion of possible experiments; each was rejected and the meeting broke up in frustration. That evening the key idea came to Schwartz: neutrinos produced when pions decay could be made in sufficient numbers to serve as a beam. A back-of-the-envelope calculation said it could work at the accelerators being built, and he phoned Lee at home. Bruno Pontecorvo had reached similar ideas independently.

With Leon Lederman, Jack Steinberger and colleagues, Schwartz built the experiment at Brookhaven’s new Alternating Gradient Synchrotron. Protons hit a beryllium target to make pions, which decayed in flight; a 13.5-metre wall of steel, made from the deck plates of a dismantled navy cruiser, stopped everything except the neutrinos; and a ten-ton spark chamber recorded the rare collisions. In 1962 the team reported that the neutrinos produced muons and almost never electrons, proving that the neutrino born with a muon is a different particle from the one born with an electron. The discovery revealed that the leptons come in families, a basic feature of the Standard Model.

The method became the standard way to study neutrinos in the laboratory. Neutrino beams made the same way, by striking a target with protons and letting the pions decay, have been built at CERN, Fermilab and J-PARC in Japan, feeding experiments such as MINOS, NOvA, OPERA and T2K that study how neutrinos change type as they travel. Schwartz, Lederman and Steinberger shared the 1988 Nobel Prize in Physics.

Why it matters

Schwartz’s neutrino beam created the field of accelerator neutrino physics and revealed the family structure of matter at the heart of the Standard Model.

About Melvin Schwartz

Bronx-born physicist who thought up the first neutrino beam and used it to show there is more than one kind of neutrino, a pillar of the Standard Model; later founded a computer security company.

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Melvin Schwartz

1932–2006 · Particle physics

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