Measurement of monoenergetic neutrons from the [Formula presented] reaction at rest

To search for baryonium states, a highly sensitive experiment with good statistics has been carried out at KEK by using an antiproton beam, deuterium target, and time-of-flight counter together with a modularized NaI(Tl) detector. At the [Formula presented] level, no narrow peaks due to the production of baryonia in the [Formula presented] reaction have been observed in the neutron spectra. At lower significance levels, however, we have observed four narrow peaks with [Formula presented], and two at an even lower significance level, in different charge-multiplicity final states. The recoil momentum distribution of the neutrons has been extracted for the channel with zero charge prongs. The energy spectra for [Formula presented] rays in coincidence with the neutron have been also obtained.