- Person
- Martin Perl
- Lived
- 1927–2014
- Field
- Particle physics
- From
- American
The story
Martin Perl was born in New York City in 1927 to Jewish parents whose families had left the Polish part of the Russian Empire to escape poverty and antisemitism. He trained as a chemical engineer and worked for General Electric before a teacher told him that what he was really interested in was physics. He earned a PhD under I. I. Rabi at Columbia in 1955 and in 1963 joined the new Stanford Linear Accelerator Center, SLAC.
At the time, physicists knew two charged leptons: the electron and the muon, which behaves almost exactly like the electron but is about 207 times heavier. Perl saw no good reason to assume there were only two. When SLAC built SPEAR, a ring that collided electrons and positrons, he proposed searching for events that no known process could produce: an electron and a muon of opposite charge, with energy missing and nothing else in the detector.
By 1974 the Mark I detector, built by Perl’s group with Burton Richter’s group and a team from Lawrence Berkeley Laboratory, had recorded 24 such events, far more than could be explained by misidentified particles. Perl challenged his colleagues to find a flaw in his reasoning, and none could. The team went public in 1975, and by 1976 the sample had grown to 139 events whose energies fitted the decay of a new heavy lepton into lighter particles and invisible neutrinos. In 1977 experiments at the German laboratory DESY confirmed it. Perl named it the tau, from the Greek word for third. It is about 3,500 times as heavy as the electron and lives for less than a trillionth of a second.
The tau was the first member of a third generation of matter. The bottom and top quarks that complete it were found later, and experiments at CERN established that there are exactly three such families. Perl shared the 1995 Nobel Prize in Physics with Frederick Reines for pioneering experimental contributions to lepton physics.
Why it matters
The tau completed the three-family pattern at the heart of the Standard Model, the theory physicists use to understand all known particles of matter, and Perl’s careful search became a model of how to find something genuinely new.
About Martin Perl
Brooklyn chemical engineer turned physicist who discovered the tau lepton, the first sign of a third family of matter particles, completing the pattern of the Standard Model. Nobel Prize 1995.
Sources
- Martin Lewis Perl (obituary) Physics Today
- Martin L. Perl, Biographical NobelPrize.org
- Nobel laureate Martin Perl dies at 87 Physics World
Another act 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.