Emission of neutron-proton and proton-proton pairs in neutrino scattering

TL;DR

This paper models neutrino-induced two-particle-two-hole emissions in carbon using relativistic meson-exchange currents, revealing dominant neutron-proton pairs and the significant role of meson-exchange mechanisms in pair emission probabilities.

Contribution

It introduces a relativistic meson-exchange current model to analyze nucleon pair emissions in neutrino scattering, highlighting the dominance of neutron-proton pairs and the impact of meson-exchange currents.

Findings

Neutron-proton pairs dominate initial state configurations.

Proton-proton emission cross section exceeds neutron-proton in certain kinematics.

Meson-exchange currents, especially $ riangle$ isobar currents, drive pair emission differences.

Abstract

We use a recently developed model of relativistic meson-exchange currents to compute the neutron-proton and proton-proton yields in $(\nu_\mu,\mu^-)$ scattering from $^{12}$C in the 2p-2h channel. We compute the response functions and cross sections with the relativistic Fermi gas model for different 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. In the case of charge-changing neutrino scattering the 2p-2h cross section of proton-proton emission ({\it i.e.,} np in the initial state) is much larger than for neutron-proton emission ({\it i.e.,} two neutrons in the initial state) by a $(\omega,q)$-dependent factor. 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 other effects including exchange contributions and the effect of the axial and vector currents.