Emission of neutron-proton and proton-proton pairs in electron scattering induced by meson-exchange currents

We use a relativistic model of meson-exchange currents to compute the proton-neutron and proton-proton yields in $(e,{e}^{\ensuremath{'}})$ scattering from $^{12}\mathrm{C}$ in the 2p-2h channel. We compute the response functions and cross section with the relativistic Fermi gas model for a range of kinematics from intermediate- to high-momentum transfers. We find a large contribution of neutron-proton configurations in the initial state, as compared to proton-proton pairs. The different emission probabilities of distinct species of nucleon pairs are produced in our model only by meson-exchange currents, mainly by the $\mathrm{\ensuremath{\Delta}}$ isobar current. We also analyze the effect of the exchange contribution and show that the direct-exchange interference strongly affects the determination of the $np/pp$ ratio.