Expressions have been obtained for the annihilation cross sections of proton pairs using weak coupling theory and spin zero mesons. The cross section for annihilation into two charged mesons has a $\frac{1}{v}$ behavior in the limit of very small velocity, $v$, of the negative proton and dominates over the annihilation into two photons. In the laboratory coordinate system it is possible for one of the emitted mesons to emerge in the backward direction with respect to the direction of the incident negative proton even for large incident energies. This may provide a method for distinguishing high energy annihilation events taking place in the cosmic radiation.

• Received 5 April 1950

DOI:https://doi.org/10.1103/PhysRev.79.266