${}^{12}$C(e,e'pN) Measurements of Short Range Correlations in the Tensor-to-Scalar Interaction Transition Region

Abstract

High-momentum configurations of nucleon pairs at short-distance are probed using measurements of the ${}^{12}$C$(e,e^{\prime }p)$ and ${}^{12}$C$(e,e^{\prime }pN)$ reactions (where $N$ is either $n$ or $p$), at high-$Q^2$ and $x_B>1.1$. The data span a missing-momentum range of 300--1000 MeV/c and are predominantly sensitive to the transition region of the strong nuclear interaction from a Tensor to Scalar interaction. The data are well reproduced by theoretical calculations using the Generalized Contact Formalism with both chiral and phenomenological nucleon-nucleon ($NN$) interaction models. This agreement suggests that the measured high missing-momentum protons up to $1000$ MeV/c predominantly belong to short-ranged correlated (SRC) pairs. The measured ${}^{12}$C$(e,e^{\prime }pN)$ / ${}^{12}$C$(e,e^{\prime }p)$ and ${}^{12}$C$(e,e^{\prime }pp)$ / ${}^{12}$C$(e,e^{\prime }pn)$ cross-section ratios are consistent with a decrease in the fraction of proton-neutron SRC pairs and increase in the fraction of proton-proton SRC pairs with increasing missing momentum. This confirms the transition from an isospin-dependent tensor $NN$ interaction at $\sim 400$ MeV/c to an isospin-independent scalar interaction at high-momentum around $\sim 800$ MeV/c as predicted by theoretical calculation.

Accepted for publication in Physics Letters B. 7 pages, 3 figures, and online supplementary materials