First measurement of $bar{ u}_{mu}$ and $ u_{mu}$ charged-current inclusive interactions on water using a nuclear emulsion detector

This paper reports the track multiplicity and kinematics of muons, charged pions, and protons from charged-current inclusive $bar{ u}_{mu}$ and $ u_{mu}$ interactions on a water target, measured using a nuclear emulsion detector in the NINJA experiment. A 3-kg water target was exposed to the T2K antineutrino-enhanced beam with a mean energy of 1.3 GeV. Owing to the high-granularity of the nuclear emulsion, protons with momenta down to 200 MeV/$c$ from the neutrino-water interactions were detected. We find good agreement between the observed data and model predictions for all kinematic distributions other than the number of charged pions. These results demonstrate the capability of measurements with nuclear emulsion to improve neutrino interaction models.