The tau lepton is a negatively charged, electron-like particle with a mass of 1.784 GeV/c2. It has a a mass of 1,777 MeV/c2. Its antiparticle is the tau-plus, which has the same mass but a positive electric charge. The tau lepton particles were discovered at SLAC in experiments at SPEAR. The 1995 Nobel Prize was awarded to Martin L. Perl from Stanford University, CA, USA, for this discovery.