25 research outputs found
Measurement of the 8B solar neutrino flux in SNO+ with very low backgrounds
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
Measurement of neutron-proton capture in the SNO+ water phase
The SNO+ experiment collected data as a low-threshold water Cherenkov
detector from September 2017 to July 2019. Measurements of the 2.2-MeV
produced by neutron capture on hydrogen have been made using an Am-Be
calibration source, for which a large fraction of emitted neutrons are produced
simultaneously with a 4.4-MeV . Analysis of the delayed coincidence
between the 4.4-MeV and the 2.2-MeV capture 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 mb
Observation of Antineutrinos from Distant Reactors using Pure Water at SNO+
The SNO+ collaboration reports the first observation of reactor antineutrinos
in a Cherenkov detector. The nearest nuclear reactors are located 240 km away
in Ontario, Canada. This analysis used events with energies lower than in any
previous analysis with a large water Cherenkov detector. Two analytical methods
were used to distinguish reactor antineutrinos from background events in 190
days of data and yielded consistent observations of antineutrinos with a
combined significance of 3.5 .Comment: v2: add missing author, add link to supplemental materia
Improved search for invisible modes of nucleon decay in water with the SNO+ detector
This paper reports results from a search for single and multi-nucleon
disappearance from the O nucleus in water within the \snoplus{} detector
using all of the available data. These so-called "invisible" decays do not
directly deposit energy within the detector but are instead detected through
their subsequent nuclear de-excitation and gamma-ray emission. New limits are
given for the partial lifetimes:
years, years, years,
years, and years at 90\% Bayesian
credibility level (with a prior uniform in rate). All but the () results improve on existing limits by a factor of about 3.info:eu-repo/semantics/publishedVersio
Search for invisible modes of nucleon decay in water with the SNO+ detector
This paper reports results from a search for nucleon decay through invisible modes, where no visible energy is directly deposited during the decay itself, during the initial water phase of SNO+. However, such decays within the oxygen nucleus would produce an excited daughter that would subsequently deexcite, often emitting detectable gamma rays. A search for such gamma rays yields limits of 2.5×1029  y at 90% Bayesian credibility level (with a prior uniform in rate) for the partial lifetime of the neutron, and 3.6×1029  y for the partial lifetime of the proton, the latter a 70% improvement on the previous limit from SNO. We also present partial lifetime limits for invisible dinucleon modes of 1.3×1028  y for nn, 2.6×1028  y for pn and 4.7×1028  y for pp, an improvement over existing limits by close to 3 orders of magnitude for the latter two
Development, characterisation, and deployment of the SNO+ liquid scintillator
A liquid scintillator consisting of linear alkylbenzene as the solvent and 2,5-diphenyloxazole as the fluor was developed for the SNO+ experiment. This mixture was chosen as it is compatible with acrylic and has a competitive light yield to pre-existing liquid scintillators while conferring other advantages including longer attenuation lengths, superior safety characteristics, chemical simplicity, ease of handling, and logistical availability. Its properties have been extensively characterized and are presented here. This liquid scintillator is now used in several neutrino physics experiments in addition to SNO+