Measurement of the Single Neutral Pion Production Cross Section in Neutral-Current Neutrino Interactions in the T2K Pi-zero Detector

Abstract

The T2K experiment is a long baseline neutrino oscillation experiment designed for the primary goal of measuring &nu_&mu \rarr &nu_e oscillation, thereby providing a measurement of the neutrino mixing angle &theta₁₃. To achieve this goal, a beam of muon neutrinos is produced at the Japanese Proton Accelerator Research Complex in Tokai, Japan and sent 295 kilometers across Japan towards the Super-Kamiokande detector. One of the major backgrounds of the &nu_e appearance measurement is from neutral current &nu_&mu interactions where a single &pi<super>0</super> is produced and the photons from the &pi<super>0</super> decay mimic the &nu_e appearance signal. To constrain the uncertainty on this background, a &pi<super>0</super>-detector has been constructed as part of the T2K near detector facility at 280 meters from the proton beam target. This dissertation presents a measurement of the neutral current single &pi<super>0</super> (NC1&pi<super>0</super>) production cross section using 8.55&times10<super>19</super> protons-on-target (POT) of T2K data. This is achieved by using pre-defined selection criteria to enhance the NC1&pi<super>0</super> signal events over background events in the invariant mass distribution of NC1&pi<super>0</super> candidate events. An extended likelihood fit is then performed on the data distribution to extract the number of signal events. We measure the ratio of the NC1&pi<super>0</super> production cross section normalized by the &nu_&mu Charged-Current Inclusive interaction to be 0.81 &plusmn 0.15 (stat) &plusmn 0.14 (sys).