50 years ago, the fundamental tau particle was discovered right here at SLAC! A series of experiments by Martin Lewis Perl with colleagues at SLAC and Berkeley Lab (LBNL) used SLAC's then-new electron–positron colliding ring, called SPEAR, and the LBNL magnetic detector, to detect and distinguish between leptons, hadrons, and photons. In 1975, they found evidence of the tau lepton, which is 3,500 times more massive than its cousin, the electron. | SLAC National Accelerator Laboratory