Measurement of the ⁸B Solar Neutrino Flux Using the Full SNO+ Water Phase

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 ²²²Rn 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 ⁸B solar neutrino analysis with a total livetime of 282.4 days and an analysis threshold of 3.5 MeV. The ⁸B solar neutrino flux is found to be (2.32+0.18-0.17(stat.)+0.07-0.05(syst.))×10⁶ cm⁻²s⁻¹ assuming no neutrino oscillations, or (5.36+0.41-0.39(stat.)+0.17-0.16(syst.) )×10⁶ cm⁻²s⁻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.