Role of Delta exchange for proton-antiproton annihilation into two-pion   and three-pion channels
  Proton-antiproton annihilation into two pions and three pions is studied in a baryon-exchange model. Annihilation diagrams involving nucleon as well as Delta-resonance exchanges are included consistently in the two- and three-pion channels. Effects from the initial-state interaction are fully taken into account. A comparison of the influence of the Delta exchange on the considered annihilation channels is made and reveals that its importance for three-pion annihilation is strongly reduced as compared to two-pion annihilation. It is found that annihilation into three uncorrelated pions can yield up to 10 % of the total experimentally observed three-pion annihilation cross section. 
M. Betz, E.A. Veit, J. Haidenbauer