Development of a boosted decision tree antineutrino photon near detector sample for T2K, and design of the Hyper-Kamiokande outer detector and DAQ

Lamers James, Menai and O'Keeffe, Helen (2024) Development of a boosted decision tree antineutrino photon near detector sample for T2K, and design of the Hyper-Kamiokande outer detector and DAQ. PhD thesis, Lancaster University.

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Abstract

The Tokai-to-Kamioka (T2K) experiment makes world-leading measurements of the neutrino oscillation parameters using a high-purity beam of (−) νµ, which are produced at the Japan Proton Accelerator Research Complex (J-PARC). They are detected at a near detector site, and at the far detector, Super-Kamiokande, 295 km away. The future Hyper-Kamiokande (Hyper-K) experiment, will make precision neutrino oscillation measurements, alongside a broad physics programme. Due to its proximity to the beam source, the T2K near detector, ND280, can constrain systematic uncertainties on the flux and cross section parameters relevant to oscillation analyses. The events are split into sub samples, and the work in this thesis describes the addition of a new ¯ν charged current sample, CC-Photon. A new boosted decision tree particle identification tool was developed to improve the purity of the sample. The CC-Photon sample selection has an efficiency of ∼40% and purity of ∼42%, making it useful for the near detector, ND, fit. Detector systematics related to the new sample were evaluated. The fractional uncertainty on the predicted event rate of the CC-Photon sample was reduced from ∼ 14% to ∼2% after adding the sample to the ND fit. Improved parameter constraints will be propagated to the far detector. Hyper-K will begin operation in 2027. It is expected to have better sensitivity to the oscillation parameters than any accelerator neutrino experiment currently in operation therefore its design must be robust. To ensure that the data acquisition system will be sufficient at handling the large quantity of data, a calculation of the detector data rate is made in this thesis. The Hyper-K outer detector is designed such that it will be efficient at detecting cosmic muon backgrounds, accounting for electronic failures which will emerge as the detector ages. Mitigation strategies are optimised in this thesis.