Muon neutrino disappearance at T2K

Abstract

This thesis measures the muon neutrino oscillation at T2K using the first data of the experiment. It concentrates on developing an original selection at Super-Kamionde, the T2K far detector, that improves the performance of the current standard selection. A new, more precise measurement of the oscillation parameters sin2 2 23 and Δm2 32 is performed using this new selection. T2K is a long-baseline neutrino oscillation experiment located in Japan which began data taking in January 2010. It uses the world’s most powerful accelerator generated beam of muon neutrinos intersected by two detectors. The near detector is located 280 m from the beam source while Super-Kamiokande lies 295 km away. Super-Kamiokande is a 50 kt water Cherenkov detector which measures the neutrino beam after oscillation. The determination of the oscillation parameters comes from looking at the disappearance of muon neutrinos from the beam. For this purpose event selection at Super-Kamiokande is optimised for neutrino flavour identification and energy reconstruction, specifically, selecting muon neutrino charged-current quasi-elastic events, primarily with single muon-like Cherenkov rings produced by the outgoing muon. This thesis evaluates two new methods of enhancing the selection to obtain a higher sensitivity from the data, firstly by exploring a multi-variate analysis approach to charged-current quasi-elastic selection, and secondly through the exploration of an additional charged-current single charged pion channel. Out of these only the multivariate based selection produced an improvement in the sensitivity to oscillation with respect to the standard selection. A first analysis of the data collected until March 11th 2011 using the above described improvement is presented in this thesis. A value of 2:68+0:12 −0:18 × 10−3 eV2 was recorded for Δm2 32 and 0:999+0:001 −0:009 for sin2 2 23. 2