Search for $hep$ solar neutrinos and the diffuse supernova neutrino background using all three phases of the Sudbury Neutrino Observatory

TL;DR

This study used the full Sudbury Neutrino Observatory dataset to search for hep solar neutrinos and the diffuse supernova neutrino background, setting new upper limits on their fluxes and finding results compatible with existing models.

Contribution

It provides the first comprehensive search for hep solar neutrinos and DSNB neutrinos using all three phases of SNO, establishing improved flux upper bounds and analyzing the data with multiple methods.

Findings

No significant hep neutrino flux detected, compatible with solar models.

No DSNB events observed, setting a new upper limit on the flux.

Improved constraints on neutrino fluxes in the relevant energy ranges.

Abstract

A search has been performed for neutrinos from two sources, the $hep$ reaction in the solar $pp$ fusion chain and the $\nu_e$ component of the diffuse supernova neutrino background (DSNB), using the full dataset of the Sudbury Neutrino Observatory with a total exposure of 2.47 kton-years after fiducialization. The $hep$ search is performed using both a single-bin counting analysis and a likelihood fit. We find a best-fit flux that is compatible with solar model predictions while remaining consistent with zero flux, and set a one-sided upper limit of $\Phi_{hep} < 30\times10^{3}~\mathrm{cm}^{-2}~\mathrm{s}^{-1}$ [90% credible interval (CI)]. No events are observed in the DSNB search region, and we set an improved upper bound on the $\nu_e$ component of the DSNB flux of $\Phi^\mathrm{DSNB}_{\nu_e} < 19~\textrm{cm}^{-2}~\textrm{s}^{-1}$ (90% CI) in the energy range $22.9 < E_\nu < 36.9$~MeV.