Di-Electrons from Resonances in Nucleon-Nucleon Collisions

TL;DR

This paper investigates how low-lying nucleon resonances contribute to di-electron production in nucleon-nucleon collisions using a covariant approach, highlighting the dominance of resonances and the significance of bremsstrahlung processes.

Contribution

It provides a comprehensive covariant and gauge invariant analysis of resonance contributions and bremsstrahlung processes in di-electron production in nucleon-nucleon collisions.

Findings

Resonances dominate di-electron spectra at 1-2 GeV.

Bremsstrahlung processes are significant in certain phase space regions.

The approach includes effective meson exchanges and resonance decays.

Abstract

The contribution of the low-lying nucleon resonances $P_{33}(1232)$, $P_{11}(1440)$ $D_{13}(1520)$ and $S_{11}(1535)$ to the invariant mass spectra of di-electrons stemming from the exclusive processes $pp\to pp e^+e^-$ and $pn\to pn e^+e^-$ is investigated within a fully covariant and gauge invariant diagrammatical approach. We employ, within the one-boson exchange approximation, effective nucleon-meson interactions including the exchange mesons $\pi$, $\eta$, $\sigma$, $\omega$ and $\rho$ as well as excitations and radiative decays of the above low-lying nucleon resonances. The total contribution of these resonances is dominant, however, bremsstrahlung processes in $pp$ and, in particular, $pn$ collisions at beam energies of 1 - 2 GeV are still significant in certain phase space regions.