Probing light dark matter and core-collapse supernova phenomena with neutrinos at SNO+

Mr Hewitt will investigate the sensitivity of SNO+ to light (sub-GeV) dark matter up-scattered by cosmic ray electrons and protons in the galactic halo, an idea prompted by a recent paper by Cappiello and Beacom (PRD 100 (2019) 10, 103011). These particles tend to evade dark matter direct detection experiments because of their low momentum, but they may leave up to O(10) MeV visible energy in SNO+.

SNO+'s exceptionally low backgrounds could improve limits (calculated by Cappiello and Beacom based on other experimental data) for this relatively unexplored range of dark matter candidates. This part of the project involves different models of the galactic halo, cosmic rays, and simplified simulation of the propagation of exotic particles through 2km of the Earth's crust, followed by full Geant4-based detector simulation of individual events.

The main focus of the second part of Mr Hewitt's project will shift to neutrinos from a (prospective but rare) galactic core-collapse supernova. He will seek to improve SNO+ sensitivity to pre-supernova neutrinos and the supernova burst by improving the detector's nearly real-time analysis of coincident events (indicative of inverse beta decay) and burst patterns (incorporating different charged and neutral-current processes).

He will also investigate strategies for increasing SNO+ acceptance of neutrino events outside the main scintillator volume, a task which will involve detailed simulation and the development of novel reconstruction techniques in areas of the detector with complicated optics. As part of this investigation, he will examine whether it is possible to extract directional information from at least some of these largely water-based events, since such events may help localize the direction of the supernova - important information to relay as quickly as possible to the astronomical observer community via the global Supernova Neutrino Early Warning System (SNEWS) network.

Mr Hewitt will also investigate the impact of a range of dark matter models on the observed time and energy spectra of the supernova neutrinos and other associated energy depositions in the detector. Understanding these effects will further inform SNO+ and other neutrino experiments as to the range of different phenomena which may be observed in the event of a galactic supernova, and improve the ability of SNEWS to produce timely, reliable, relevant information for subsequent real-time observations, as well as correlation with both electromagnetic and gravitational "messengers".