Selection rules governing the annihilation of a nucleon-antinucleon pair into pions, photons, and heavy mesons are derived from the conservation of angular momentum, parity, charge parity, and isotopic spin. Special attention is given to the probability of annihilation purely into neutral pions.

• Received 6 February 1956

DOI:https://doi.org/10.1103/PhysRev.103.258