Measurement of lead-target neutrino interactions using the whole T2K near detector

Abstract

This thesis presents a selection of neutrino interactions occurring within the Electromagnetic Calorimeters (ECals) of the T2K off-axis near detector, ND280. ND280 is situated 2.5 degrees off axis with respect to the J-PARC neutrino beam and is used to constrain the unoscillated neutrino flux for T2K oscillation analyses. The motivation for an ECal-target sample is three-fold: to investigate the neutrino flux across a wider range of off-axis angles than is possible with the main near-detector target; to measure the rate of muon production with a larger angular acceptance than the standard near detector event samples; and to investigate neutrino interactions on lead, a heavy nuclear target on which there is little published data. To enable this analysis, the ECal vertex reconstruction was integrated with the rest of the ND280 reconstruction software. For the first time, the accurate particle identification (PID) and momentum reconstruction capabilities of the ND280 Tracker are used for particles produced in neutrino interactions in the ECals. PID and kinematic reconstruction is not possible using ECal information alone. Using this newly facilitated reconstruction of ECal-originating final-state particles, distributions of the reconstructed kinematics for a sample of charged-current inclusive muon-neutrino interaction candidates are compared between data and simulation. This highlights that a deficiency in the ND280 simulation of entering background particles constitutes a more significant problem than previously believed. The data--simulation agreement seen is reasonable: the shape-only Chi-Square test statistic for the muon-like sample was evaluated to be 245 for 104 analysis bins. This motivates the further use of the ND280 ECals for constraint of the T2K flux prediction as well as heavy-target, neutrino scattering measurements.

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