Measurement of Atmospheric Flux-Weighted Charged-Current $\nu_{e} - {}^{16}\text{O}$ Cross Section with the Super-Kamiokande Experiment

Abstract

A first measurement of $\nu_{e} + {}^{16}\text{O} \to e^{-} + {}^{16}\text{F}^{*}$ cross section from 45 MeV to 125 MeV was performed using the atmospheric neutrinos incident to the Super-Kamiokande detector over 24 years. This corresponds to an exposure of 485 kTon$\cdot$years, and 125 (after cuts) expected $\nu_{e} - {}^{16}\text{O}$ events between 45 and 125 MeV. An event generator to simulate $\nu_{e} - {}^{16}\text{O}$ interactions, a multivariate method to separate events with de-excitation gammas, and an unbinned likelihood fitter to extract the flux-weighted cross section are developed. Using these tools, a scaling factor of $1.87^{+0.35\text{(stat)}+0.62\text{(syst)}}_{-0.36\text{(stat)}-0.34\text{(syst)}}$ to the Haxton prediction was measured, corresponding to $233^{+89}_{-62}$ observed events and an atmospheric $\nu_{e}$ flux-weighted cross section of $10.8^{+4.1}_{-3.0} \times 10^{-40} \text{cm}^{2}$. This is $1.7\sigma$ larger than the Haxton prediction of $5.8 \times 10^{-40} \text{cm}^{2}$, and $3.6\sigma$ away from the null hypothesis. The measured ratio can be used to rescale the $\nu_{e} - {}^{16}\text{O}$ cross section in supernova burst studies and diffuse supernova neutrino background searches. Finally, atmospheric neutrinos at this energy range will be a background for the future WIMP dark matter searches via coherent elastic neutrino-nucleus scattering. Combined with an independent $\nu_{e} - {}^{16}\text{O}$ cross section measurement, this measurement can be used to constrain the uncertainties in the low energy atmospheric neutrino flux, which is relevant for the estimation of the WIMP neutrino floor.