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

We measured inclusive \ensuremath{\gamma}-ray spectra from p\ifmmode\bar\else\textasciimacron\fi{}p annihilation at rest to search for narrow \ensuremath{\gamma} 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\ensuremath{\sigma}. The 4\ensuremath{\sigma} upper limits for the yield of p\ifmmode\bar\else\textasciimacron\fi{}p\ensuremath{\rightarrow}\ensuremath{\gamma}B times the decay branching ratio of B into ${N}_{\mathrm{ch}}$-prong states is (1.2--0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ at \ensuremath{\gamma}-ray energy of 80--938 MeV for the sum over ${N}_{\mathrm{ch}}$, (0.3--0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ for each of ${N}_{\mathrm{ch}}$=0 and \ensuremath{\ge}6, and (0.8--0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ for each of ${N}_{\mathrm{ch}}$=2 and 4. At 2 to 3\ensuremath{\sigma} levels, however, we have seen nine narrow \ensuremath{\gamma}-ray peaks with individual yields between ${10}^{\mathrm{\ensuremath{-}}4}$ and ${10}^{\mathrm{\ensuremath{-}}3}$ for various charge multiplicities.