Search for a light short-lived neutral boson in orthopositronium decay

Abstract

We have searched for the decay of orthopositronium (o-Ps) into a gamma quantum and a light neutral short-lived boson under the assumption that the latter subsequently decays into two photons: o-Ps→ γa →2 γ . The upper limit for the ratio of this decay rate to the 3γ decay rate obtained is Γ(o-Ps→ γa)/ Γ(o-Ps→3 γ)<2.8×10 −5 at the 90% confidence level provided that the boso n mass m a<30 keV and the life time τ a[ s]<10 −13× m a [keV]. This result excludes the hypothesis that this decay may resolve the discrepancy between the theoretical and experimental o-Ps life time in vacuum.