Detection of back-to-back proton pairs in charged-current neutrino interactions with the ArgoNeuT detector in the NuMI low energy beam line

Short range nucleon-nucleon correlations in nuclei ($NN$ SRC) carry important information on nuclear structure and dynamics. $NN$ SRC have been extensively probed through two-nucleon knockout reactions in both pion and electron scattering experiments. We report here on the detection of two-nucleon knockout events from neutrino interactions and discuss their topological features as possibly involving $NN$ SRC content in the target argon nuclei. The ArgoNeuT detector in the Main Injector neutrino beam at Fermilab has recorded a sample of 30 fully reconstructed charged-current events where the leading muon is accompanied by a pair of protons at the interaction vertex, 19 of which have both protons above the Fermi momentum of the Ar nucleus. Out of these 19 events, four are found with the two protons in a strictly back-to-back high momenta configuration directly observed in the final state and can be associated to nucleon resonance pionless mechanisms involving a pre-existing short range correlated $np$ pair in the nucleus. Another fraction (four events) of the remaining 15 events has a reconstructed back-to-back configuration of an $np$ pair in the initial state, a signature compatible with one-body quasielastic interaction on a neutron in a short range correlation (SRC) pair. The detection of these two subsamples of the collected (${\ensuremath{\mu}}^{\ensuremath{-}}+2p$) events suggests that mechanisms directly involving nucleon-nucleon SRC pairs in the nucleus are active and can be efficiently explored in neutrino-argon interactions with the Liquid Argon Time Projection chamber technology.