New 2-ring $\nu_e$ CC1$\pi^+$ samples at the T2K Far Detector

Abstract

The Tokai-to-Kamioka (T2K) experiment is a long-baseline accelerator neutrino experiment in Japan that measures the leptonic CP-violating phase $\delta_{CP}$ by studying $\nu_e$ appearance from the $\nu_\mu$ beam at T2K's far detector, Super-Kamiokande (SK). The near detector (ND280) stands 280 metres, and SK stands 295 km away from the beam production target. SK is a 50 kton water-Cherenkov detector that observes Cherenkov rings from charged particles produced in neutrino interactions with water. Both single and multi-ring samples for $\nu_\mu$ at SK are used in T2K's latest oscillation analyses, while for $\nu_e$, only single-ring samples are used. Charged current single $\pi^+$ (CC1$\pi^+$) events form the second most dominant signal events in $\nu_e$ appearance studies, of which events with $\pi^+$ below Cherenkov threshold are used in the latest analysis (1 $e$-like ring and a decay electron signature). The addition of the sample with $\pi^+$ above the Cherenkov threshold, consisting of an $e$-like ring and a $\pi^+$-like ring can increase the statistics of $\nu_e$ events and thus our sensitivity to $\delta_{CP}$. In this proceeding, cuts-based selection of these 2-ring $\nu_e$ CC1$\pi^+$ events will be discussed.