A search for neutrino-induced single photons and measurement of oscillation analysis systematic errors with electron and anti-electron neutrino selections, using the o -axis near detector of the Tokai to Kamioka experiment

Abstract

This thesis describes the search for neutrino-production of single photons using the o - axis near detector at 280 metres (ND280) of the T2K experiment. A photon selection is used to perform the searches using the rst Fine Grained Detector (FGD1) of the ND280. The thesis also highlights the importance of systematic uncertainties in the analysis, since the selection is background dominated. After careful characterisation of the systematic uncertainties and estimation of the e ciency, it is concluded that, with the selected 39 data events and the expected background of 45 events, the limit for neutrino-induced single photons, at T2K energies, is 0:0903 x 10-38cm2=nucleon. This result can be com- pared with the expected limit of 0:1068 x 10-38cm2=nucleon. Using ND280's neutrino energy distribution (peaked at 600 MeV), NEUT predicts a ux-averaged cross section of 0:000239 x 10-38cm2=nucleon. A t to the muon and electron (anti-) neutrinos selections in the ND280 was per- formed. The aim of this analysis is to use a data-driven method to constrain the electron (anti-) neutrinos background events at SK, the far detector and electron neutrino cross section parameters for oscillation analyses. These are fundamental inputs in the context of the searches for Charge-Parity (CP) violation in the neutrino sector. After a t to the nominal Monte Carlo was realised, the electron neutrino and anti-neutrino cross sec- tion normalisation uncertainties are found to be 7:6% and 19:3%, repectively. Although these numbers are much higher than the assumed 3% uncertainty of all the CP violation searches performed at T2K up to now, the difference in the CP log-likelihood is found to be acceptable as the one sigma contours are not very di erent and the exclusion of the CP = 0 is roughly the same.