Measuring the electron anti-neutrino beam component in the T2K near detector ND280

TL;DR

This paper measures the electron anti-neutrino component in the T2K near detector, confirming background predictions and developing selection methods for anti-neutrino interactions to explore CP violation.

Contribution

It introduces a method to quantify the electron neutrino contamination and extends the selection techniques to electron anti-neutrinos in the T2K experiment.

Findings

Measured a data/MC ratio of 1.01 ± 0.10 for the ν_e component

Confirmed predictions of background levels in the beam

Developed selection criteria for ν̄_e charged-current interactions

Abstract

The main irreducible background in the T2K $\nu_e$ appearance analysis is the $\nu_e$ contamination in the $\nu_\mu$ beam. In order to quantify this background, a selection for charged-current $\nu_e$ interactions in the near detector (ND280) tracker region was developed by combining the particle identification abilities of the time projection chambers and electromagnetic calorimeters. We measured a data/MC ratio of $1.01 \pm 0.10$ for the $\nu_e$ component of the beam which, is an important confirmation of our predictions of the expected backgrounds. In 2014 the T2K experiment reversed the polarity of the magnetic horns and began running with an antineutrino beam for the first time. Differences in the oscillation probabilities between neutrinos and antineutrinos may provide insight into CP violation in the leptonic sector. The current ND280 Tracker $\nu_e$ charged-current selection has been used as a starting point for the $\bar{\nu_e}$ charged-current selection. The additional challenges and selection criteria of the electron anti-neutrino selection will be presented.