Veneziano model for low-energy nucleon-nucleon phase-shifts and high-energy charge-exchange cross-sections

Abstract

A phenomenological model is constructed for low-energy nucleon-nucleon scattering (≲400 MeV) and high-energy np and p\(\bar p\) charge-exchange scattering (≳5 GeV) based on the Veneziano representation. The major advantage of the Veneziano representationvs. the usual OBE models for low-energy phase-shift calculations is that it provides a natural no-cut-off model. It is found that theS-waves and the higher partial waves can be reproduced with comparable accuracy using theN/D method with four adjustable parameters. These are the two ρ-meson coupling constants, the ɛ-meson coupling constant and the coupling constant of a pion conspirator. Although the conspirator coupling has little effect on the low-energy phase shifts, its existence is demanded by the self-consistency of the Veneziano representation. At high energies, the conspirator plays an essential role in reproducing the forward peak in charge-exchange scatterings. However, the data indicate that it is necessary to suppress the ρ contribution and introduce a phase factor differing from that of the simple Veneziano model. A two-parameter modification of the ρ trajectory along with the given π and π conspirator trajectories yields a satisfactory fit to both the np ((5 ÷ 24) GeV) and the p\(\bar p\) ((6 ÷ 9) GeV) data.