Pion-Pair Production in a Nuclear Emulsion

Abstract

A positive and a negative $\pi$-meson pair of tracks with energies of 17.94 and 18.65 Mev, respectively, are observed to originate in an emulsion without any other associated ionizing particles. It is shown that the event probably did not originate from a nuclear collision. Among the mechanisms considered are materialization from a photon, the decay of a theta-meson, and decay of a (previously postulated) zeta meson. The $Q$-value of the event, computed as a 2-body decay is 27.9 Mev. If it is a two-body decay the mass of the parent particle is about 600 $m_e$. This event is also consistent with the decay of a neutral tau meson into a neutral pion and two charged pions for which the total kinetic energy of the charged mesons could vary between 0 and about 80 Mev.