An experimental limit on the coupling of a light neutral pseudoscalar particle to hadrons

Abstract

Detailed results of an experiment, looking for a short-lived neutral particle decaying by an e⁺ e^- pair in the decay of the 3.68 MeV (3/2) state in ¹³C, whose decay is predominantly M1, are presented. An upper limit of 7×10^-5 has been placed on the branching ratio for decay through such a particle with a mass in the range 1.7 to 1.9 MeV/c². This leads to an upper limit of 10^-6 for the coupling of such a particle to nucleons. Such a limit rules out the explanation of the e⁺ and e^- peaks recently observed in heavy ion collisions, as due to the decay of a neutral particle.