This paper presents a measurement of the charged current interaction rate of the electron neutrino beam component of the beam above 1.5 GeV using the large fiducial mass of the T2K ${\pi }^0$ detector. The predominant portion of the ${\nu }_e$ flux ($\sim 85\%$) at these energies comes from kaon decays. The measured ratio of the observed beam interaction rate to the predicted rate in the detector with water targets filled is $0.89\pm 0.08(\text{stat})\pm 0.11(\text{sys})$, and with the water targets emptied is $0.90\pm 0.09(\text{stat})\pm 0.13(\text{sys})$. The ratio obtained for the interactions on water only from an event subtraction method is $0.87\pm 0.33(\text{stat})\pm 0.21(\text{sys})$. This is the first measurement of the interaction rate of electron neutrinos on water, which is particularly of interest to experiments with water Cherenkov detectors.

• Received 30 March 2015

DOI:https://doi.org/10.1103/PhysRevD.91.112010

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Published by the American Physical Society