Professor Martin Perl, US particle physicist at the Stanford Linear Accelerator Center (SLAC) in Stanford, California. Perl was a member of the team headed by Burton Richter which co-discovered the J/psi particle - the first evidence of the charm quark - at the SPEAR electron-positron collider at SLAC in 1974. In the same year, Perl used the same detector at SPEAR - the Mark 1 - to discover the tau lepton particle, the heavy relative of the electron & muon; this was the first hint of a third generation of leptons & quarks. Photographed at SLAC in 1984, Perl is seen standing inside the disassembled Mark II detector, the successor to the Mark I.