Abstract
This paper reports the track multiplicity and kinematics of muons, charged pions, and protons from charged-current inclusive $\bar{\nu}_{\mu}$ and $\nu_{\mu}$ 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.
Highlights
In accelerator-based long-baseline neutrino oscillation experiments, neutrino interactions with the nuclei are essential processes for measuring the neutrino oscillation parameters and searching for CP violation in the lepton sector [1,2,3,4,5,6]
Events with a single lepton and no other visible particles are selected as the signals, and the incoming neutrino energies are reconstructed from only the outgoing leptons assuming the two-body kinematics of the chargedcurrent quasielastic (CCQE) interaction
After the viewer and manual checks, 97 events remain as interactions on water, 182 events remain as interactions on iron, and 71 events are excluded as misconnected tracks or interactions in the emulsion films
Summary
In accelerator-based long-baseline neutrino oscillation experiments, neutrino interactions with the nuclei are essential processes for measuring the neutrino oscillation parameters and searching for CP violation in the lepton sector [1,2,3,4,5,6]. At present, the measurement of the 2p2h interaction is poor, because the momentum threshold for protons is not sufficiently low to detect all the protons from the neutrino interactions. Precise measurements of interactions including lowmomentum charged pions in the final state are important. They contaminate the signals at SK when the pions fall short of the Cherenkov threshold in water, Michel-electron tagging can sometimes be used to veto such events. Measurements of protons and pions from neutrino interactions with low momentum thresholds play an important role in constructing reliable models of the neutrino-nucleus interactions and reducing the systematic uncertainties in T2K. A new experiment using a nuclear emulsion detector was proposed to measure protons from neutrino-water interactions with a momentum threshold as low as 200 MeV=c.
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