Global Extraction of the $\rm^{12}C$ Nuclear Electromagnetic Response Functions (${\cal R}_L$ and ${\cal R}_T$) and Comparisons to Nuclear Theory and Neutrino/Electron Monte Carlo Generators

Abstract

We have performed a global extraction of the ${\rm ^{12}C}$ longitudinal (${\cal R}_L$) and transverse (${\cal R}_T$) nuclear electromagnetic response functions from an analysis of all available electron scattering data on carbon. The response functions are extracted for energy transfer $\nu$, spanning the nuclear excitation, quasielastic (QE), resonance and inelastic continuum over a large range of the square of the four-momentum transfer ($Q^2$), for fixed values of $Q^2$ and for fixed values of 3-momentum transfer $\bf q$. The data sample consists of approximately 10,000 differential electron scattering and photo-absorption-cross section measurement points for ${\rm ^{12}C}$. In addition, we perform a universal fit to all ${\rm ^{12}C}$ electron scattering data which also provides parmeterizations of ${\cal R}_L$ and ${\cal R}_T$ over a larger kinematic range. Since the extracted response functions and the universal fit cover a large range of $Q^2$ and $\nu$, they can be readily used for comparison to theoretical predictions as well as validating and tuning Monte Carlo generators for electron and neutrino scattering experiments. In this paper we focus on the nuclear excitation, QE, and $\Delta$(1232) regions and compare the measurements to predictions of the following theoretical approaches: ``Energy Dependent-Relativistic Mean Field'' (ED-RMF), ``Green's Function Monte Carlo'' (GFMC), "Short Time Approximation Quantum Monte Carlo" (STA-QMC), "Correlated Fermi Gas" (CFG), as well as the {\textsc{NuWro}}, \ {{\sc{achilles}}}~ and {{\sc{genie}}}~generators. We find that among all the models ED-RMF provides the best description of both the QE and {\it nuclear excitations} response functions over the largest kinematic range $0.01\le Q^2 \le 1.25$ GeV$^2$. The ED-RMF formalism has the added benefit that it should be directly applicable to the same kinematic regions for neutrino scattering.