Proton-proton bremsstrahlung calculation: Studies of the off-shell proton electromagnetic vertex and of pseudoscalar vs pseudovectorπNcouplings

Abstract

The proton-proton bremsstrahlung $(pp\ensuremath{\gamma})$ process has been used as a tool to study the problems related to both the off-shell proton electromagnetic vertex and pseudoscalar (ps)-pseudovector (pv) $\ensuremath{\pi}N$ coupling. We have developed an approach which can be applied to investigate the two problems together. We show that (i) the analyzing powers calculated using the on-shell $p\ensuremath{\gamma}p$ vertex, with ps or pv coupling, yield very poor results for most of the cases with small proton scattering angles at 280 MeV, (ii) the calculations using the off-shell $p\ensuremath{\gamma}p$ vertex and ps coupling in most cases produce cross sections which fail to fit the TRIUMF data at 200 and 280 MeV, and (iii) the data for both cross sections and analyzing powers in the energy region between 157 and 280 MeV can only be consistently described by the calculations using the off-shell $p\ensuremath{\gamma}p$ vertex and pv coupling. Thus our results indicate that the off-shell $p\ensuremath{\gamma}p$ vertex must be used in relativistic $\mathrm{pp}\ensuremath{\gamma}$ calculations and the pseudovector coupling is the best choice for the $\ensuremath{\pi}N$ vertex. More accurate data are needed for further study of the problems.