PION PRODUCTION IN NUCLEON-NUCLEON COLLISIONS AT THRESHOLD

We present a theory of soft-pion production by nucleons which provides a connection between the production amplitude and nucleon-nucleon scattering. This is done by applying the algebra of currents to the S-matrix element for the process γ+2n→2N+π. After reducing out both the photon and pion, the hypothesis of partially conserved axial-vector current is used to replace the pion field by the divergence of the axial-vector current. Using the current commutation relations, we then obtain the pion production amplitude in terms of the amplitude for photoproduction of a pion on two nucleons, plus a correction integral which vanishes in the soft-pion limit. Upon taking the soft-photon-soft-pion limit, only certain pole terms survive. In this way, pion production is directly related to off-shell nucleon-nucleon scattering. Results are presented for the reactions pp→npπ+, np→ppπ-, and pp→ppπ0. The theoretical predictions are found to be in good agreement with the cross-section data near threshold for π- and π0 production, and with an extrapolation from higher-energy data for π+ production. © 1969 The American Physical Society.