Martin Lewis Perl
1927–2014, New York City, New York, USA, Palo Alto, California, USA
American physicist who shared the 1995 Nobel Prize in Physics for discovering the tau lepton, the first member of a third generation of leptons.
Born in Brooklyn to a family of Jewish immigrants, Perl studied chemical engineering before earning a physics PhD at Columbia in 1955 under Isidor Rabi. He joined SLAC in 1963 and designed the experiments at the SPEAR electron–positron collider that in 1975 revealed anomalous e–μ events: pairs of an electron and a muon with missing energy, produced by the decay of a heavy new lepton — the tau (τ). The tau implied a whole third generation of matter, confirmed later by the bottom quark (1977) and tau neutrino (2000).
Nobel-winning work
In 1974–1975 the SLAC–LBL collaboration running the Mark I detector at SPEAR observed events e⁺e⁻ → e⁺μ⁻ (and e⁻μ⁺) with nothing else detected — impossible under known two-lepton physics. Perl recognized them as sequential decays of a pair-produced heavy lepton, τ⁺τ⁻, each tau decaying to an electron or muon plus neutrinos.
Published in Physical Review Letters in 1975 ('Evidence for Anomalous Lepton Production…'), the tau discovery showed leptons, like quarks, replicate in generations — completing the three-generation picture of matter particles in the Standard Model.
Workplaces: SLAC National Accelerator Laboratory, Stanford University
United States