Emission of neutron-proton and proton-proton pairs in electron scattering induced by meson-exchange currents

TL;DR

This paper models meson-exchange currents in electron scattering from carbon-12, revealing significant neutron-proton pair emissions influenced mainly by the $elta$ isobar current, with interference effects impacting pair ratio analysis.

Contribution

It introduces a relativistic model that quantifies the emission of nucleon pairs in electron scattering, emphasizing the role of meson-exchange currents and interference effects.

Findings

Large neutron-proton emission compared to proton-proton pairs.

Meson-exchange currents, especially $elta$ isobar, dominate pair emission.

Exchange interference significantly affects np/pp ratio determination.

Abstract

We use a relativistic model of meson-exchange currents to compute the proton-neutron and proton-proton yields in $(e,e')$ scattering from $^{12}$C in the 2p-2h channel. We compute the response functions and cross section with the relativistic Fermi gas model for a range of kinematics from intermediate to high momentum transfers. We find a large contribution of neutron-proton configurations in the initial state, as compared to proton-proton pairs. The different emission probabilities of distinct species of nucleon pairs are produced in our model only by meson-exchange currents, mainly by the $\Delta$ isobar current. We also analyze the effect of the exchange contribution and show that the direct/exchange interference strongly affects the determination of the np/pp ratio.