Relativistic two-body currents for one-nucleon knockout in electron-nucleus scattering

TL;DR

This paper investigates the impact of two-body electromagnetic currents on one-nucleon knockout in electron-nucleus scattering using a relativistic mean-field model, proposing approximations for computational efficiency and validating against experimental data.

Contribution

It introduces simplified approximations for two-body current calculations within a relativistic framework, maintaining accuracy while reducing computational complexity.

Findings

Excellent agreement with experimental data for the longitudinal response.

Two-body currents significantly enhance the transverse response, improving data agreement.

Approximations are validated against full models, ensuring reliability.

Abstract

We present a detailed study of the contribution from two-body currents to the one-nucleon knockout process induced by electromagnetic interaction. The framework is a relativistic mean-field model (RMF) in which bound and scattering nucleons are consistently described as solutions of Dirac equation with potentials. We show results obtained with the most general expression of the two-body operator, in which the intermediate nucleons are described by relativistic mean-field bound states; then, we propose two approximations consisting in describing the intermediate states as nucleons in a relativistic Fermi gas, preserving the complexity and consistency in the initial and final states. These approximations simplify the calculations considerably, allowing us to provide outcomes in a reasonable computational time. The results obtained under these approximations are validated by comparing with those from the full model. Additionally, the theoretical predictions are compared with experimental data of the longitudinal and transverse responses of carbon 12. The agreement with data is outstanding for the longitudinal response, where the contribution from the two-body operator is negligible. In the transverse sector, the two-body current increases the response from 30 to 15%, depending on the approximations and kinematics, in general, improving the agreement with data.