Search for Axion-Like Particles in the SLAC Beam Dump.

A search for axion-like particles was made at the Stanford Linear Accelerator Center (SLAC) by dumping 30 Coulombs of 20 GeV electrons into a beam absorption facility. After 179 meters of earth shielding the in-flight decay of the particle into two photons or an electron-positron pair, in a decay volume of 204 meters in length, was searched for with a fine-grained electromagnetic calorimeter. No positive signals were identified. Experimental limits were obtained for axions of mass up to ~200 MeV/c^{2}, and photinos of mass up to ~65 MeV/c^{2 }.