Measurement of the ${}^8$B Solar Neutrino Flux Using the Full SNO+ Water Phase Dataset

The SNO+ detector operated initially as a water Cherenkov detector. The implementation of a sealed covergas system midway through water data taking resulted in a significant reduction in the activity of ${}^{222}$Rn daughters in the detector and allowed the lowest background to the solar electron scattering signal above 5 MeV achieved to date. This paper reports an updated SNO+ water phase ${}^8$B solar neutrino analysis with a total livetime of 282.4 days and an analysis threshold of 3.5 MeV. The ${}^8$B solar neutrino flux is found to be $\left(2.32_{-0.17}^{+0.18}{\text{(stat.)}}_{-0.05}^{+0.07}\text{(syst.)}\right)\times {10}^6$ cm${}^{-2}$s${}^{-1}$ assuming no neutrino oscillations, or $\left(5.36_{-0.39}^{+0.41}{\text{(stat.)}}_{-0.16}^{+0.17}\text{(syst.)}\right)\times {10}^6$ cm${}^{-2}$s${}^{-1}$ assuming standard neutrino oscillation parameters, in good agreement with both previous measurements and Standard Solar Model Calculations. The electron recoil spectrum is presented above 3.5 MeV.