Search

T2K is an accelerator-based neutrino oscillation experiment providing World-leading measurements of the atmospheric oscillation parameters. These measurements are made by comparing observed event rates with the unoscillated expectations based on Monte Carlo constrained by a near detector complex and external data. The comparisons are made across several data samples based on the type and number of rings observed in the Superkamiokande (SK) water Cherenkov far detector. Due to their similar masses, muons and pions generate similar signatures in SK. Thus, neutral current (NC) events producing a single observable charged pion in the final state form a significant background in the most relevant signal samples for atmospheric oscillation parameters. Despite accounting for less than 3% of the total selected interactions this background has a large systematic uncertainty on its overall cross-section normalization, leading to a total event rate systematic uncertainty comparable to that of the much more numerous CCQE signal events. In addition, the localized nature of these background events in the energy spectrum and their relatively complex energy smearing make them an important nuisance. The statistical errors will decrease over the next few years as T2K continues to collect data. Hence, constraining the systematic error of this background is expected to significantly benefit the future determination of the atmospheric parameters. Single charged pion production in NC neutrino-nucleus interactions has only been studied a handful of times, with the most recent published studies dating from more than four decades ago. A new selection of these events in the T2K ND280 detector, along with preliminary performance metrics will be presented.

Parallel Contributed Talk at the "XIX International Workshop on Neutrino Telescopes" on line - 18-26 February, 2021, On behalf of the T2K Collaboration