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Abstract:

The $\mathrm{SNO}+$ Collaboration reports the first evidence of ${}^8\mathrm{B}$ solar neutrinos interacting on ${}^{13}\mathrm{C}$ nuclei. The charged current interaction proceeds through ${}^{13}\mathrm{C}+{\mathrm{ν}}_e{→}^{13}\mathrm{N}+e^{−}$ which is followed, with a 10 minute half life, by ${}^{13}\mathrm{N}{→}^{13}\mathrm{C}+e^{+}+{\mathrm{ν}}_e$ . The detection strategy is based on the delayed coincidence between the electron and the positron. Evidence for the charged current signal is presented with a significance of $4.2\mathrm{σ}$ . Using the natural abundance of ${}^{13}\mathrm{C}$ present in the scintillator, 5.7 metric tons of ${}^{13}\mathrm{C}$ over 231 days of data were used in this analysis. The ${5.6}_{−2.3}^{+3.0}$ observed events in the data set are consistent with the expectation of ${4.7}_{−1.3}^{+0.6}$ events. This result is the second real-time measurement of CC interactions of ${}^8\mathrm{B}$ neutrinos with nuclei and constitutes the lowest energy observation of neutrino interactions on ${}^{13}\mathrm{C}$ generally. This enables the first direct measurement of the CC ${\mathrm{ν}}_e$ reaction to the ground state of ${}^{13}\mathrm{N}$ , yielding an average cross section of $({16.1}_{−6.7}^{+8.5}(\mathrm{stat}\mathrm{.}{)}_{−2.7}^{+1.6}(\mathrm{syst}\mathrm{.}))×{10}^{−43}{\mathrm{cm}}^2$ over the relevant ${}^8\mathrm{B}$ solar neutrino energies.

Abstract:

$\mathrm{SNO}+$ Collaboration reports its second spectral analysis of reactor antineutrino oscillation using 286 ton-yr of new data. The measured energies of reactor antineutrino candidates were fitted to obtain the second-most precise determination of the neutrino mass-squared difference $\mathrm{Δ}{m}_{21}^2=({7.96}_{−0.42}^{+0.48})×{10}^{−5}{\mathrm{eV}}^2$ . Constraining $\mathrm{Δ}{m}_{21}^2$ and ${\sin }^2{\mathrm{θ}}_{12}$ with measurements from long-baseline reactor antineutrino and solar neutrino experiments yields $\mathrm{Δ}{m}_{21}^2=({7.58}_{−0.17}^{+0.18})×{10}^{−5}{\mathrm{eV}}^2$ and ${\sin }^2{\mathrm{θ}}_{12}=0.308Â\pm 0.013$ . This fit also yields a first measurement of the flux of geoneutrinos in the Western Hemisphere, with ${73}_{−43}^{+47}$ TNU at $\mathrm{SNO}+$ .

Abstract:

In the DEAP-3600 dark matter search experiment, precise reconstruction of the positions of scattering events in liquid argon is key for background rejection and defining a fiducial volume that enhances dark matter candidate events identification. This paper describes three distinct position reconstruction algorithms employed by DEAP-3600, leveraging the spatial and temporal information provided by photomultipliers surrounding a spherical liquid argon vessel. Two of these methods are maximum-likelihood algorithms: the first uses the spatial distribution of detected photoelectrons, while the second incorporates timing information from the detected scintillation light. Additionally, a machine learning approach based on the pattern of photoelectron counts across the photomultipliers is explored.