Meson Production in Antiproton-Nucleon Annihilation

Abstract

The antiproton-nucleon system at rest and its annihilation are discussed. Final states of two mesons, of many mesons with all but one in a vector resonance, and of two vector resonances are the main concern, al though the decay to lepton pairs and other properties of the ;p-nucleon system are also considered. The basic assumptions are that annihilations proceed mainly through an intermediate vector meson (^^i decay) or pseudoscalar meson p5o decay) and also that SU{3) symmetry is vaUd for obtaining unknown coupling constants. The unknown parameters in the SU(3) couplings are determined by fitting to experiment, with the following interesting results: gpNN^gwNN and gn*NN^-'2girNNi where ry* refers to the 960-MeV rjirir resonance, and the above coupling constants for the p and со are the sum of the уц and a^vq^ coefficients. gpNN'^gaNN at 52= -4mjv^ is shown to be consistent with nuclear-force calculations around ?^=0, and the above value for g,*^-j^helps explain the rapid increase with energy of the proton Compton-scattering cross section. The SU(3) EBV interaction is determined from the rates for ^^i annihilations of pp to ir^ifir^, тг^тГ, K'^K", and K\K2, the VVP coupling from w -> Зтг and ф -^ Зтг, and the BBP interaction from the ^SQ decays of pp to K^R*, pYy and />V. We discuss briefly the relation of the SU{S) coupUngs determined here and the results of broken SU{6) and U{12). In particular, we show that d/f^l for BBV at §2= ~4m^, in contradiction to the value | given by SU{6) and U{X2); we also conclude that the d/f ratio is not constant for the BBV coupling. A table of relative rates and graphs of expected mass spectra are given for final states consisting of a vector resonance plus pseudoscalar meson, and a comparison with the available experi mental evidence is made. The approximate agreement expected is observed. The discussion of the vectorvector final states leads to the prediction that Т(рр-^р^р^)^Т{рр->са^оз^), and we also determine that (pp -»e'^e~)/(pp ->• ir+TT") »2X 10-5. Finally we conclude that the assumptions made are thus far consistent with experiment. ^ The proposition that the deuteron ought to be regarded as a bound state of proton and neutron has had public debate. See S. Weinberg, Phys. Rev. 137, B672 (1965).