First evidence of neutrino absorption on argon using ${}^8$B solar neutrinos in DEAP-3600

Abstract

We report experimental evidence for electron neutrino charged-current interactions (neutrino absorption, CC $\hat{I}{½}_e$) from ${}^8$B solar neutrinos on ${}^{40}$Ar using an exposure of ($7.29\pm 0.05$) tonne$\cdot$years in the DEAP-3600 detector. A region of interest (ROI) of 10.5-13.0 MeV reconstructed energy calibrated on single-peak events, corresponding to incident neutrino energy in 12.0-14.5 MeV, is used for this measurement. We observe 5 single-peak and 1 double-peak neutrino-like events consistent with the ${}^8$B solar neutrino energy spectrum in the ROI after correcting for nonlinearities in the detector response at high energies. With an expected background of $0.48{}_{-0.15}^{+0.16}$ events, the data correspond to a significance of $4.0\ddot{I}ƒ$ with respect to the background-only hypothesis. We report an energy-averaged cross section of $(4.0{}_{-1.6}^{+2.0}(\mathrm{stat}){}_{-0.7}^{+0.8}(\mathrm{sys}))\times 10^{-41}{\mathrm{cm}}^2$ in the ROI for the CC $\hat{I}{½}_e$ signal, a factor $(2.4{}_{-1.0}^{+1.3})$ higher than predicted by Bhattacharya, Goodman and García (2009).

6 pages, 3 figures