Parity Nonconservation in Elastic $\vec{p} p$ Scattering

Abstract

By looking at the parity-nonconserving (PNC) asymmetries at different energies in $\vec{p} p$ scattering, it is in principle possible to determine the PNC $\rho NN$ and $\omega NN$ couplings of a single-meson-exchange model of the PNC $NN$ force. The analysis of the experimental data at 13.6, 45 and 221 MeV simultaneously has been performed by Carlson \textit{et al.}, who concluded to an agreement with the original DDH estimates for the PNC meson-nucleon couplings. In this work, it is shown first that the comparison with updated hadronic predictions of these couplings rather suggests the existence of some discrepancy for the PNC $\omega NN$ coupling. The effect of variations on the strong coupling constants and introduction of cutoffs in the one-boson-exchange weak potential is then investigated. As expected, it turns out that the resulting asymmetry is quite sensitive to these parameters regardless of the energy. However the above discrepancy persists. The dependence of this conclusion on various ingredients entering an improved description of the PNC $NN$ force is also examined. These include the two-pion resonance nature of the rho meson and some momentum dependence of the isoscalar PNC $\rho NN$ vertex. It is found that none of these corrections is able to remove or even alleviate the above discrepancy. Their impacts on the theoretical determination of the vector meson-nucleon couplings, the description of the PNC force in terms of single-meson exchanges, or the interpretation of measurements, are finally examined.