Search for narrow states by detection of monochromatic gamma rays in p¯p annihilation at rest

We measured inclusive -ray spectra from pp annihilation at rest to search for narrow lines associated with the production of baryonia. The measurement was done with statistics several times as high as those of earlier experiments by using modularized NaI(Tl) detectors. We have not observed any narrow states, i.e., baryonium candidates, with statistical significance higher than 4. The 4 upper limits for the yield of ppB times the decay branching ratio of B into Nch-prong states is (1.20.2)×10-3 at -ray energy of 80938 MeV for the sum over Nch, (0.30.1)×10-3 for each of Nch=0 and 6, and (0.80.1)×10-3 for each of Nch=2 and 4. At 2 to 3 levels, however, we have seen nine narrow -ray peaks with individual yields between 10-4 and 10-3 for various charge multiplicities.