Search for short-lived axions in an electron-beam-dump experiment

Results of an electron-beam-dump search for neutral particles with masses in the range 1 to 15 MeV and lifetimes tau of between 10 to the -14th and 10 to the -10th s are reported. No evidence was found for such an object. The existence of any 1.8-MeV pseudoscalar boson with tau of greater than 8.2 x 10 to the -15th s and an absorption cross section in matter less than 1 mb per nucleon is ruled out; and tau of greater than 10 to the -14th s is excluded were its cross section to equal 50 mb per nucleon. In conjunction with measurements of the electron's anomalous magnetic moment, this experiment shows that the narrow positron peaks observed in heavy-ion collisions at the Gessellschaft fuer Schwerionenforschung are not due to an elementary pseudoscalar. (Author)