Study of the neutral current interaction with a 0 in the nal state in the ND280 detector of the T2K experiment

Abstract

The Tokai to Kamioka (T2K) experiment is designed to detect ! e appearance for the rst time from accelerator generated neutrinos and measure neutrino oscillation parameters. The most intense accelerator muon neutrino beam ever built is produced at the J-PARC facility on the East coast of Japan, and sent 2.5 o -axis toward the Super-Kamiokande water Cherenkov detector. The main background for the recent appearance analysis comes from neutral current 1 0 interaction, accounting for 23% of the background events. In addition, the near detector (ND280) has been built to serve the requirement to provide high accuracy beam characteristics and background studies by measuring a number of neutrino cross-sections. In this thesis the NC1 0 channel studies at the near detector ND280 is performed. The studies aim to develop the NC1 0 event selection to single out the muon neutrino induced NC1 0 interactions in the P D ( 0 Detector) sub- detector, where one 0 decay gamma converts in the P D and the second gamma converts in the P D-ECal ( 0 Electromagnetic Calorimeter) sub-detector. The used data sample was collected during Runs II,III and IV, consisting of a total of 6:2 1020 POT. Simulated events are generated with the NEUT MC to eval- uate backgrounds and estimate the selection effi ciency. The studies have been performed for the two P D confi gurations: fi lled with water and without water.The fi rst approach to the usage of P D-ECal sub-detector in the NC1 0 channel studies showed that further improvements on the P D-ECal reconstruction and matching between the P D and P D-ECal is required. However, as a result of the performed analysis the total e ciency of 3.0% (4.0%) and purity of 17.7% (16.4%) is obtained for the P D fi lled with water (without water) con guration. Finally, after selection, 68 8:2 (stat) (107 10:3 (stat)) events passed all the requirements for the P D fi lled with (without) water. The developed selection lay the groundwork for the future measurement of the NC1 0 cross-section for the events induced by neutrinos interacting in the P D sub-detector and systematic errors evaluation, using larger data sets. As for now, the systematic uncertainties are a subject of a discussion in this thesis.