Antiproton-Proton Annihilation into Electron-Positron Pairs and Gamma-Ray Pairs

Experimental limits have been set on the cross sections for p̄+p→e⁺+e^- for antiprotons with incident momenta of 1.47 and 2.40 GeV/c. These results imply upper limits on the magnitude of the proton form factors for timelike four-momentum transfer of 5.1 and 6.6 (GeV/c)². The reaction p̄+p→γ+γ has been studied at the same incident momenta. This process has apparently been observed for incident antiproton momentum of 1.47 GeV/c, while an upper limit for the two-photon annihilation cross section is found at 2.40-GeV/c incident momentum.