Mapping the tensor-to-scalar transition in the short-range nucleon-nucleon interaction

The predominance of proton-neutron short-range correlated pairing for nucleons with $\approx$300--600~MeV$/c$ of relative momentum is now well-understood as a consequence of the tensor force in the nucleon-nucleon ($NN$) interaction. The isospin structure of pairs with even higher relative momenta can reveal new information about the interactions between nucleons at extremely short distance scales. I will present the results of new measurements of the $(e,e'p)$, $(e,e'pp)$, and $(e,e'pn)$ reactions in high-$Q^2$, $x_B>1$ kinematics in the missing momentum range of 300--1000~MeV$/c$. The data are well reproduced by theoretical calculations using Generalized Contact Formalism with both chiral and phenomenological $NN$ interaction models. This agreement between the theory and data suggests that all of the measured high missing-momentum protons belong to SRC pairs. Furthermore, the results show clear evidence of a transition from an isospin-dependent tensor-$NN$ interaction at $\approx 400$~MeV$/c$ to an isospin-independent scalar interaction at high-momentum around $\approx 800$~MeV$/c$.