Anomalous internal pair creation in Be-8 as a signature of the decay of a new particle

In a measurement of the angular correlation of e(+)e(-) pairs in the isovector M1 decay from 1(+) level at 17.64 MeV in Be-8, a large deviation was found from quantum electrodynamics(QED)-prediction for internal pair conversion (IPC). By postulating the emission of a neutral particle with a mass of 12 (2.5) MeV/c(2) the structure of the angular correlation can be described.