UBC Theses and Dissertations
Measurement of an off-axis neutrino beam energy spectrum Kirby, Brian
The T2K long baseline neutrino oscillation experiment is designed to measure the neutrino flavour mixing parameter θ₁₃, as well as θ₂₃ and Δm²₂₃ with twenty times greater precision than previous measurements. A neutrino beam is produced using the Japan Proton Accelerator Research Complex (J-PARC) proton accelerator in Tokai, Japan and is incident on the Super-Kamiokande water Cherenkov detector 295 km away beam at an off-axis angle of 2.5°. A suite of near detectors 280 m away from the proton target (ND280) provides additional constraints on beam flux estimates as well as measures neutrino interaction cross sections. A critical component of ND280 is a Fine Grained Detector (FGD) that provides an active target for neutrino interactions, with sufficient granularity to reconstruct short ranged particle tracks. This thesis describes the T2K experiment, the design and calibration of the FGD, and its online data reduction system. A cut-based selection for charged current neutrino interactions is used to produce quasi-elastic and non-quasi-elastic enhanced samples. These samples are used in a maximum likelihood fit to measure the T2K neutrino beam energy spectrum. The fit determines the flux scale factors that best reproduce the kinematic distribution of muons produced in selected interactions, and accounts for all relevant neutrino interaction model and detector systematic uncertainties. The fitted flux factors f(Eν) in the energy ranges defined for the analysis are as follows: f(0 < Eν < 0.5GeV ) = 1.10⁺⁰·²⁸₋₀.₂₄, f(0.5 < Eν < 1.0GeV ) = 0.93⁺⁰·¹⁷₋₀.₁₄, f(1.0 < Eν < 3.5GeV ) = 0.85⁺⁰·¹⁷₋₀.₁₄, f(Eν > 3.5GeV ) = 0.92⁺⁰·²⁸₋₀.₂₃. These flux factors are consistent with the default neutrino beam flux prediction and the flux measurement used in the primary oscillation analysis of the T2K collaboration, and provide an independent confirmation that the neutrino beam flux model is reliable.
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