SEARCH FOR MILLICHARGED PARTICLES AT SLAC

Particles with electric charge q less than or equal to 10(-3) e and ma sses in the range 1-100 MeV/c(2) are not excluded by present experimen ts. An experiment uniquely suited to the production and detection of s uch ''millicharged'' particles has been carried out at SLAG. This expe riment is sensitive to the infrequent excitation and ionization of mat ter expected from the passage of such a particle. Analysis of the data rules out a region of mass and charge, establishing, for example, a 9 5%-confidence upper limit on electric charge of 4.1 x 10(-5) e for mil licharged particles of mass 1 MeV/c(2) and 5.8 x 10(-4) e for mass 100 MeV/c(2). [S0031-9007(98)06790-8].