A search for a baryonium in P-bar P annihilation at rest

In order to search for a baryonium below the threshold of twice of the nucleon mass, we have measured inclusive gamma (γ) spectra in P-bar P annihilation at rest using the KEK proton synchrotron. With higher statistical accuracy than previous experiments, no narrow structure which has statistical significance larger than 4σ was observed. The 4σ upper limit for the production of narrow baryonium states in γ energy range 80-938 MeV (the mass of the baryonium is lower than 1794.8 MeV/C2) was found to be (0.2-1.2)x10-3 of all annihilations. We also analyzed the decay branching ratio into various charge multiplicity (Nch) states and found no narrow structure which was larger than 4σ. The 4σ upper limits were (0.1-0.3)x10-3, (0.1-0.8)x10-3, (0.1-0.8)x10-3, and (0.1-0.3)x10-3 for each Nch=0,2,4, and ≥6 states. (author) 53 refs. 14 tabs. 57 figs