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

TL;DR

This paper reports a precise measurement of the $^8$B solar neutrino flux using the SNO+ detector's water phase data, achieving low background levels and confirming consistency with solar models and previous experiments.

Contribution

First measurement of $^8$B solar neutrino flux with the SNO+ detector's water phase, utilizing reduced background from a new covergas system.

Findings

Measured $^8$B flux assuming no oscillations: (2.32^{+0.18}_{-0.17})×10^6 cm^{-2}s^{-1}

Measured $^8$B flux with oscillations: (5.36^{+0.41}_{-0.39})×10^6 cm^{-2}s^{-1}

Results agree with previous measurements and Standard Solar Model predictions.

Abstract

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 $\left(2.32^{+0.18}_{-0.17}\text{(stat.)}^{+0.07}_{-0.05}\text{(syst.)}\right)\times10^{6}$ cm$^{-2}$s$^{-1}$ assuming no neutrino oscillations, or $\left(5.36^{+0.41}_{-0.39}\text{(stat.)}^{+0.17}_{-0.16}\text{(syst.)} \right)\times10^{6}$ 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.