Negaton-positon pair creation in pion-nucleon interactions

Abstract

Recently, in two experiments [1, 2] for the η 0 study, electron pairs at large angle have been found. π + N → N + e + + e − . The number of events is relatively small and some estimates of total cross sections have been made. Process (1) is evidently related to pion electroproduction. The only difference is the sign of the invariant square mass of the virtual photon. In the electroproduction experiments, the transfer is space-like while in the pair-production experiments it is time-like. The e +e − pair-production experiments are particularly interesting because they permit to measure the nucleon form factors in a range 0 ≤ k 2 ≤ 4 m 2 N, which are out of reach for electroproduction or annihilation experiments. The differential cross section for pair production in the one-photon exchange approximation is very simply related to the transverse and longitudinal inverse pion photoproduction with a virtual photon. An evaluation of the differential cross section and of the total cross section for pair production has been made. Comparison with experiments gives an experiments gives an excellent agreement. An experiment at the N ∗ 3 2 3 2 resonance energy is suggested to give the nucleon form factor for time-like transfer up to k 2 = 2.5 fm −2.