Daniel Barrow

Abstract:

A simultaneous beam and atmospheric oscillation analysis that combines the T2K and SK experiments has been presented. The first sensitivities of the joint analysis are reported, with the intention for the two collaborations to publish a data analysis in the near-future. This analysis leverages the different energies and baselines of the two experiments and provides strong sensitivities on δCP, sin2(θ23) and ∆m232. To do this, a Bayesian Markov Chain Monte Carlo technique is utilised to generate parameter estimates and credible intervals. Constraints from the T2K near detector are also used to constrain the uncertainties of both beam and atmospheric predictions.

For a known set of oscillation parameters close to the preferred values from a T2K-only data fit, the sensitivity of the joint analysis to sin2(θ23) is increased compared to the beam-only analysis, illustrated by a 7% reduction in the width of the 1σ credible interval. Furthermore, the sensitivity of the joint analysis to select the correct mass hierarchy hypothesis is drastically improved compared to the beam-only analysis, culminating in a substantial preference as classified by Jeffrey’s scale. This statement is stronger than the sensitivity of the beam-only analysis, either with or without external constraints on sin2(θ13). The sensitivities of the beam-only and joint beam-atmospheric analyses have also been compared for a known set of oscillation parameters which are CP-conserving. The joint analysis displays an improved ability to select the correct phase of δCP and octant of sin2(θ23) compared to the beam-only analysis. This thesis illustrates the benefit of the combined beam and atmospheric analysis, which could also be extended for use in the next-generation Hyper-Kamiokande experiment.