MEC-induced two-nucleon emission in neutrino-nucleus scattering

Meson-exchange currents (MEC) play a crucial role in the nuclear response to a leptonic probe, inducing the emission of two nucleons, the so-called 2p2h excitations. Here we report the results of our recent work \cite{Belocchi:2025eix}, in which we evaluated the 2p2h contribution to the $(\nu_\mu,\mu^-p)$ neutrino cross section off a carbon target, which involves the simultaneous detection the outgoing muon and a proton in the final state. This process has recently been measured in long-baseline neutrino experiments, but no truly microscopic calculation for the 2p2h channel existed to be compared with these data until now. The calculation employs fully relativistic two-body currents and is carried out within the Relativistic Fermi Gas framework. It provides a generalization to the weak sector of the electromagnetic inclusive model developed in Ref.~\cite{DePace:2003spn} and an extension of the calculation to enable semi-inclusive predictions. A selection of our results for the semi-inclusive cross section versus the emitted proton variables is presented, both at fixed neutrino energy and folded with the T2K muon-neutrino flux.