Constraining neutrino interaction parameters using the T2K off-axis near detector ND280 with a 4π solid angle sample selection

Xu, Yongheng and Kormos, Laura (2023) Constraining neutrino interaction parameters using the T2K off-axis near detector ND280 with a 4π solid angle sample selection. PhD thesis, Lancaster University.

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Abstract

The Tokai-to-Kamioka (T2K) experiment is a long-baseline neutrino study designed to measure neutrino oscillation parameters, including θ13, θ23, ∆m232, and δCP . In the ex- periment, a proton beam is directed at a carbon target, generating a neutrino flux that is first measured by the Near Detector at 280 m (ND280) at the Japan Proton Accel- erator Research Complex (J-PARC) on Japan’s east coast and subsequently measured by the Super-Kamiokande (SK) detector, located 295 km away. By comparing the data from both detectors, researchers can extract crucial information about neutrino oscillation parameters. Previously in the ND280 measurements, only charged-current neutrino interaction events featuring a forward-going final-state muon were employed. This thesis presents a novel approach by developing a set of selection criteria for charged-current events with muons in any direction relative to the neutrino flux. This advancement is achieved using time-of-flight information between ND280 sub-detectors. A correction was also developed to compensate for known data-simulation discrepancy. Ten new subsamples have been created, and their associated systematic uncertainties have been assessed. These samples have been tested in the T2K near detector fitter, BANFF, resulting in improved constraints for numerous parameters compared to previ- ous samples, as evidenced by test runs and validations. This will ultimately lead to an improved understanding of the neutrino oscillation parameters.