Interaction current in $p p \to p p \gamma$

TL;DR

This paper develops a gauge-invariant relativistic model for proton-proton bremsstrahlung, introducing a phenomenological contact current to accurately describe experimental data and resolve previous theoretical discrepancies.

Contribution

It introduces a generalized contact current approach to account for the interaction current in proton-proton bremsstrahlung within a relativistic meson-exchange model.

Findings

Good agreement with high-precision experimental data at 190 MeV

Resolves longstanding discrepancy between theory and experiment

Highlights importance of interaction current in reaction modeling

Abstract

The nucleon-nucleon bremsstrahlung reaction is investigated based on a fully gauge-invariant relativistic meson-exchange model approach. In order to account consistently for the complicated part of the interaction current (which at present is too demanding to be calculated explicitly), a generalized contact current is introduced following the approach of Haberzettl, Nakayama, and Krewald [Phys. Rev. C74, 045202 (2006)]. The contact interaction current is constructed phenomenologically such that the resulting full bremsstrahlung amplitude satisfies the generalized Ward-Takahashi identity. The formalism is applied to describe the high-precision proton-proton bremsstrahlung data at 190 MeV obtained at KVI [H. Huisman et al., Phys. Rev. C65, 031001(R) (2002)]. The present results show good agreement with the data, thus removing the longstanding discrepancy between the theoretical predictions and experimental data. The present investigation, therefore, points to the importance of properly taking into account the interaction current for this reaction.