Doyle, Tristan and O'Keeffe, Helen (2022) Development of New Off-Axis Near Detector Samples for the T2K Oscillation Analysis. PhD thesis, Lancaster University.
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Abstract
The Tokai-to-Kamioka (T2K) experiment is a long-baseline (anti)neutrino experiment designed to make world-leading measurements of several of the parameters that describe neutrino oscillations: $\theta_{13}$, $\theta_{23}$, $\Delta m^2_{23}$ and $\delta_{CP}$. The experiment uses a beam of muon (anti)neutrinos produced at the Japan Proton Accelerator Research Complex (J-PARC) which is categorised by a suite of near detectors before oscillation samples are selected at the far detector, Super-Kamiokande. Charged Current (CC) $\nu_{\mu}$ interactions in the near detector ND280 are categorised based on reconstructed final state particles. The resulting samples are fitted to near detector data to provide constraints on flux and cross section systematic uncertainties in the oscillation analysis. In this thesis, a new selection of CC $\nu_{\mu}$ interactions in the ND280 detector that produce final state photons is developed. The new photon sample has an efficiency of 43.0$\pm$0.1\% (43.9$\pm$0.1\%) and a purity of 53.9$\pm$0.2\% (54.2$\pm$0.2\%) in FGD1 (FGD2). Detector systematic uncertainties associated with the new selections are also evaluated. The new photon sample, along with a new proton tag, are used in a new categorisation of CC $\nu_{\mu}$ interactions at the near detector in the oscillation analysis. One of the fitting methods used to fit the near detector data is described in this thesis. The new near detector samples are used to constrain uncertainties in the flux and cross section models used in the analysis, reducing the uncertainties on the far detector event rates.