Measurement of neutron-proton capture in the SNO+ water phase
Physical Review C American Physical Society 102:1 (2020) 014002
Abstract:The SNO+ experiment collected data as a low-threshold water Cherenkov detector from September 2017 to July 2019. Measurements of the 2.2-MeV γ's produced by neutron capture on hydrogen were made using an Am-Be calibration source, for which a large fraction of emitted neutrons are produced simultaneously with a 4.4-MeV γ. Analysis of the delayed coincidence between the 4.4-MeV γ and the 2.2-MeV capture γ revealed a neutron detection efficiency that is centered around 50% and varies at the level of 1% across the inner region of the detector, which to our knowledge is the highest efficiency achieved among pure water Cherenkov detectors. In addition, the neutron capture time constant was measured and converted to a thermal neutron-proton capture cross section of 336.3+1.2−1.5mb.
Search for invisible modes of nucleon decay in water with the SNO+ detector
Physical Review D American Physical Society (APS) 99:3 (2019) 032008
Measurement of the 8B solar neutrino flux in SNO+ with very low backgrounds
Physical Review D American Physical Society 99:1 (2019) 012012
Abstract:A measurement of the 8B solar neutrino flux has been made using a 69.2 kt-day dataset acquired with the SNO+ detector during its water commissioning phase. At energies above 6 MeV the dataset is an extremely pure sample of solar neutrino elastic scattering events, owing primarily to the detector’s deep location, allowing an accurate measurement with relatively little exposure. In that energy region the best fit background rate is 0.25+0.09−0.07 events/kt−day, significantly lower than the measured solar neutrino event rate in that energy range, which is 1.03+0.13−0.12 events/kt−day. Also using data below this threshold, down to 5 MeV, fits of the solar neutrino event direction yielded an observed flux of 2.53+0.31−0.28(stat)+0.13−0.10(syst)×106 cm−2 s−1, assuming no neutrino oscillations. This rate is consistent with matter enhanced neutrino oscillations and measurements from other experiments.
Slow Fluors for Highly Effective Separation of Cherenkov Light in Liquid Scintillators
Abstract:The timing and spectral characteristics of four highly efficient, slow fluors are presented for liquid scintillator solutions using linear alkylbenzene (LAB) as the primary solvent. The mixtures exhibit high light yields, but with rise times of several ns or more and decay times on the order of tens of ns. Consequently, such liquid scintillator mixtures can be used for highly effective separation of Cherenkov and scintillation components based on timing in large scale liquid scintillation detectors. Such a separation, showing high light yield and directional information, is demonstrated here on a bench-top scale for electrons with energies extending below 1 MeV. This could have significant consequences for the future development of such detectors for measurements of solar neutrinos and neutrinoless double beta decay as well as providing good directional information for elastic scattering events from supernovae neutrinos and reactor anti-neutrinos, amongst others.
Multi-site event discrimination in large liquid scintillation detectors
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Elsevier 943 (2019) 162420