Abstract

Annihilation of antiprotons and protons at rest into neutral particles has been studied with the
Crystal Barrel detector at LEAR. Annihilation frequencies are determined for final states containing
!0, ", "" and # mesons using a liquid and a room temperature, 12 bar, gaseous hydrogen target.
Including annihilation frequencies for production of neutral kaons from other experiments, the
identified reactions for annihilation in liquid hydrogen add up to a branching fraction of (3.56 ± 0.28)% per annihilation compared to the frequency of (3.50±0.30)%withwhichwe observe the allneutral
decay modes inclusively. Since the exclusive final states are normalized to the Crystal Barrel
measurement of the !0!0 branching ratio, the latter result is strongly supported by this present study.