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 $2.47\mathrm{kton}\text{−}\mathrm{years}$ 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 ${\mathrm{\Phi }}_{hep}<30\times {10}^3{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ [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 ${\mathrm{\Phi }}_{{\nu }_e}^{\mathrm{DSNB}}<19{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ (90% CI) in the energy range $22.9<E_{\nu }<36.9\mathrm{MeV}$.

• Received 15 July 2020
• Accepted 1 September 2020

DOI:https://doi.org/10.1103/PhysRevD.102.062006

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Published by the American Physical Society