Meson-exchange currents and nuclear correlations in neutrino and electron scattering with nuclei

TL;DR

This thesis investigates meson-exchange currents and short-range correlations in electron and neutrino scattering on nuclei, improving models and analyzing their effects on response functions and cross sections.

Contribution

It introduces an improved SuSAM* model incorporating MEC and SRC effects, providing new phenomenological scaling functions and detailed analysis of their impact on scattering responses.

Findings

MEC significantly affect electromagnetic and neutrino response functions.

SRC increase the high-momentum components and response functions.

Interference effects between one- and two-body currents are negative and reduce cross sections.

Abstract

This thesis is dedicated to the study of electron and neutrino scattering on nuclei, with special emphasis on meson-exchange currents (MEC) and short-range correlations (SRC) between nucleon pairs in one-particle emission processes. In chapter 2, the SuSAM* model is improved by redefining the single nucleon hadronic tensor, averaging it over a Fermi distribution instead of using the previous extrapolation from the relativistic Fermi gas. This formulation removes the inconsistency associated with negative contributions in kinematics far from the QE peak. The new definition allows extending the SuSAM* formalism to include MEC, which is the focus of chapter 3. In chapter 3, a scaling analysis of 12C data is performed incorporating MEC explicitly at the single nucleon level, leading to a new phenomenological scaling function. Using this model, the effect of MEC on EM responses is studied and compared with the relativistic Fermi gas (RFG) and the relativistic mean field (RMF) models. Chapter 4 presents a detailed analysis of the interference between 1b2b in the RT. It is shown that this interference is always negative within the independent-particle approximation. Chapter 5 extends the study of MEC to the CCQE neutrino scattering within the RFG, RMF, and SuSAM* frameworks. It is found that OB-MEC interference reduces both the RT and the neutrino cross section. Chapter 6 addresses SRC in the wave function of a nucleon pair in nuclear matter. The BG equation is solved using the NN potential developed by the Granada group, allowing for the calculation of high-momentum components. Finally, chapter 7 combined the effect of MEC and SRC, which extends the FG by including the high-momentum components of nucleon pairs affected by MEC. It is found that SRC enhance the RT, in contrast with what is observed in uncorrelated models.