Inclusive transverse response of nuclear matter

Abstract

The electromagnetic inclusive transverse response of nuclear matter at saturation density is studied within the correlated basis function perturbation theory for momentum transfers $q$ from $300$ to 550 MeV/$c$. The correlation operator includes a Jastrow component, accounting for the short range repulsion, as well as longer range spin, tensor, and isospin ones. Up to correlated one-particle--one-hole intermediate states are considered. The spreading due to the decay of particle (hole) states into two-particle--one-hole (two-hole--one-particle) states is considered via a realistic optical potential model. The Schiavilla-Pandharipande-Riska model for the two-body electromagnetic currents, constructed so as to satisfy the continuity equation with realistic ${v}_{14}$ potentials, is adopted. Currents due to intermediate $\ensuremath{\Delta}$-isobar excitations are also included. The global contribution of the two-body currents turns out to be positive and provides an enhancement of the one-body transverse response ranging from $\ensuremath{\sim}20%$ for the lower momenta to $\ensuremath{\sim}10%$ for the higher ones. This finding is in agreement with the Green's function Monte Carlo studies of the transverse Euclidean response in $A=3,4$ nuclei and contradicts previous results obtained within the Fermi gas and shell models. The tensor-isospin component of the correlation is found to be the leading factor responsible for such a behavior. The nuclear matter response is compared to recent experimental data on ${}^{40}$Ca and ${}^{56}$Fe.