Number 244 (Story #1), October 11, 1995 by Phillip F. Schewe and Ben Stein THE PHYSICS NOBEL PRIZE GOES TO MARTIN PERL OF SLAC AND FREDERICK REINES OF UC IRVINE for their discoveries of elementary particles. Perl led the team of scientists that found the tau lepton in electron-positron collisions in 1975. In his experiment at the SPEAR collider at SLAC, high energy electrons and positrons were smashed together head on; among the particles created out of the energy of collision were pairs of new particles, later identified as the tau and antitau, each with a mass of about 1.8 GeV. The tau and its associated neutrino are the fifth and sixth (and perhaps last) of a family of particles known as leptons. The six known leptons, along with the six quarks, are the basic alphabet from which all the other constituents of ordinary atomic matter are made. Reines, working with Clyde Cowan (who died in 1974) made the first experimental detection of a neutrino (to be exact, the electron antineutrino), another member of the lepton family. The existence of neutrinos had been predicted in 1930 by Wolfgang Pauli as a way of accounting for the energy that seemed to be missing from reactions in which neutrons decayed into protons. In the early 1950s Reines and Cowan successfully sought evidence for the neutrino in an experiment, at a reactor at Savannah River, SC, in which a neutrino interacted with a proton to create a neutron plus a positron.