Detailed results of an experiment, looking for a short-lived neutral particle decaying by ane+e− pair in the decay of the 3.68 MeV (3/2) state in13C, 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 thee+ ande− peaks recently observed in heavy ion collisions, as due to the decay of a neutral particle.
