We report results from a combined analysis of solar neutrino data from all phases of the Sudbury Neutrino Observatory (SNO). By exploiting particle identification information obtained from the proportional counters installed during the third phase, this analysis improved background rejection in that phase of the experiment. The combined analysis of the SNO data resulted in a total flux of active neutrino flavors from ${}^8\mathrm{B}$ decays in the Sun of $(5.25\pm 0.16{(\mathrm{stat}.)}_{-0.13}^{+0.11}(\mathrm{syst}.))\times {10}^6{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, while a two-flavor neutrino oscillation analysis yielded $\Delta m_{21}^2=(5.6_{-1.4}^{+1.9})\times {10}^{-5}{\mathrm{eV}}^2$ and ${\tan }^2{\theta }_{12}=0.{427}_{-0.029}^{+0.033}$. A three-flavor neutrino oscillation analysis combining the SNO result with results of all other solar neutrino experiments and reactor neutrino experiments yielded $\Delta m_{21}^2=(7.{46}_{-0.19}^{+0.20})\times {10}^{-5}{\mathrm{eV}}^2$, ${\tan }^2{\theta }_{12}=0.{443}_{-0.025}^{+0.030}$, and ${\sin }^2{\theta }_{13}=(2.{49}_{-0.32}^{+0.20})\times {10}^{-2}$.

SNO+ is a large liquid scintillator-based experiment located 2 km underground at SNOLAB, Sudbury, Canada. It reuses the Sudbury Neutrino Observatory detector, consisting of a 12 m diameter acrylic vessel which will be filled with about 780 tonnes of ultra-pure liquid scintillator. Designed as a multipurpose neutrino experiment, the primary goal of SNO+ is a search for the neutrinoless double-beta decay (0νββ) of¹³⁰Te. In Phase I, the detector will be loaded with 0.3% natural tellurium, corresponding to nearly 800 kg of¹³⁰Te, with an expected effective Majorana neutrino mass sensitivity in the region of 55–133 meV, just above the inverted mass hierarchy. Recently, the possibility of deploying up to ten times more natural tellurium has been investigated, which would enable SNO+ to achieve sensitivity deep into the parameter space for the inverted neutrino mass hierarchy in the future. Additionally, SNO+ aims to measure reactor antineutrino oscillations, low energy solar neutrinos, and geoneutrinos, to be sensitive to supernova neutrinos, and to search for exotic physics. A first phase with the detector filled with water will begin soon, with the scintillator phase expected to start after a few months of water data taking. The0νββPhase I is foreseen for 2017.

The Sudbury Neutrino Observatory (SNO) used an array of ${}^3\mathrm{He}$ proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (${\nu }_x$) ${}^8\mathrm{B}$ solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be ${5.54}_{-0.31}^{+0.33}(\mathrm{\text{stat}}{)}_{-0.34}^{+0.36}(\mathrm{\text{syst}})\times {10}^6{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields $\Delta m^2={7.59}_{-0.21}^{+0.19}\times {10}^{-5}{\mathrm{eV}}^2$ and $\theta ={34.4}_{-1.2}^{+1.3}$ degrees. The uncertainty on the mixing angle has been reduced from SNO’s previous results.

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers $0.12\le Q^2\le 1.0{\mathrm{GeV}}^2$. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, $Q^2$ dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.

Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is $T_{\mathrm{eff}}=3.5$ MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of ${10}^6$ cm${}^{-2}$ ${\mathrm{s}}^{-1}$, the total flux of active-flavor neutrinos from ${}^8\mathrm{B}$ decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the ${}^8\mathrm{B}$ neutrino energy spectrum, is found to be ${\Phi }_{\mathrm{NC}}=5.{140}_{-0.158}^{+0.160}{\text{(stat)}}_{-0.117}^{+0.132}\text{(syst)}.$ These uncertainties are more than a factor of 2 smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the Sudbury Neutrino Observatory data in which the free parameters directly describe the total ${}^8\mathrm{B}$ neutrino flux and the energy-dependent ${\nu }_e$ survival probability provides a measure of the total ${}^8\mathrm{B}$ neutrino flux ${\Phi }_{{}^8\mathrm{B}}=5.{046}_{-0.152}^{+0.159}{\text{(stat)}}_{-0.123}^{+0.107}\text{(syst)}$. Combining these new results with results of all other solar experiments and the KamLAND reactor experiment yields best-fit values of the mixing parameters of ${\theta }_{12}=34.{06}_{-0.84}^{+1.16}$ degrees and $\Delta m_{21}^2=7.{59}_{-0.21}^{+0.20}\times {10}^{-5}$ eV${}^2$. The global value of ${\Phi }_{{}^8\mathrm{B}}$ is extracted to a precision of ${}_{-2.95}^{+2.38}\%$. In a three-flavor analysis the best fit value of $\sin {}^2{\theta }_{13}$ is $2.{00}_{-1.63}^{+2.09}\times {10}^{-2}$. This implies an upper bound of $\sin {}^2{\theta }_{13}<0.057$ ($95\%$ C.L.).

This article provides the complete description of results from the Phase I data set of the Sudbury Neutrino Observatory (SNO). The Phase I data set is based on a 0.65 kiloton-year exposure of ${}^2{\mathrm{H}}_2$O (in the following denoted as ${\mathrm{D}}_2$O) to the solar ${}^8\mathrm{B}$ neutrino flux. Included here are details of the SNO physics and detector model, evaluations of systematic uncertainties, and estimates of backgrounds. Also discussed are SNO's approach to statistical extraction of the signals from the three neutrino reactions (charged current, neutral current, and elastic scattering) and the results of a search for a day-night asymmetry in the ${\nu }_e$ flux. Under the assumption that the ${}^8\mathrm{B}$ spectrum is undistorted, the measurements from this phase yield a solar ${\nu }_e$ flux of $\varphi ({\nu }_e)=1.{76}_{-0.05}^{+0.05}(\mathrm{stat}.){}_{-0.09}^{+0.09}(\mathrm{syst}.)\times {10}^6$ cm${}^{-2}$ s${}^{-1}$ and a non-${\nu }_e$ component of $\varphi ({\nu }_{\mu \tau })=3.{41}_{-0.45}^{+0.45}(\mathrm{stat}.){}_{-0.45}^{+0.48}(\mathrm{syst}.)\times {10}^6$ cm${}^{-2}$ s${}^{-1}$. The sum of these components provides a total flux in excellent agreement with the predictions of standard solar models. The day-night asymmetry in the ${\nu }_e$ flux is found to be $A_e=7.0\pm 4.9(\mathrm{stat}.){}_{-1.2}^{+1.3}\%(\mathrm{syst}.)$, when the asymmetry in the total flux is constrained to be zero.