Martin Perl (1927MB-2014), US physicist. Perl is best known for his discovery of the tau lepton in a series of experiments between 1974 and 1977 at at the SPEAR electron-positron collider at the Stanford Linear Accelerator Center (SLAC). The tau is a heavier version of the electron. He received a share of the 1995 Nobel Prize in Physics for this discovery. Perl was also a member of the team at SLAC headed by Burton Richter that co-discovered the J/psi particle, the first evidence of the charm quark, in 1974. Photographed at (SLAC), Menlo Park, California, USA, in 1988.