A search for photonless annihilation of orthopositronium

Abstract

We have searched for the photonless annihilation of orthopositronium, o-Ps → nothing (nothing denotes the weakly-interacting particles which are not detected). The upper limit on the ratio of this decay rate to the 3γ decay rate obtained is Γ(o-Ps → nothing)/ Γ(o-Ps → 3 γ) < 5.8 × 10 −4 (90% CL). This result excludes the hypothesis that this decay is responsible for the discrepancy between the theoretical and experimental values of the orthopositronium lifetime in vacuum.