Observations of neutral-current $\nu$ interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current (NC), elastic scattering, and charged current reactions and assuming the standard ${}^8\mathrm{B}$ shape, the ${\nu }_e$ component of the ${}^8\mathrm{B}$ solar flux is ${\phi }_e{=1.76\mathrm{}}_{-0.05\mathrm{}}^{+0.05\mathrm{}}\left(\mathrm{stat}{)}_{-0.09\mathrm{}}^{+0.09\mathrm{}}\right(\mathrm{syst})\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$ for a kinetic energy threshold of 5 MeV. The non- ${\nu }_e$ component is ${\phi }_{\mu \tau }{=3.41\mathrm{}}_{-0.45\mathrm{}}^{+0.45\mathrm{}}\left(\mathrm{stat}{)}_{-0.45\mathrm{}}^{+0.48\mathrm{}}\right(\mathrm{syst})\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$, $5.3\sigma$ greater than zero, providing strong evidence for solar ${\nu }_e$ flavor transformation. The total flux measured with the NC reaction is ${\phi }_{\mathrm{NC}}{=5.09\mathrm{}}_{-0.43\mathrm{}}^{+0.44\mathrm{}}\left(\mathrm{stat}{)}_{-0.43\mathrm{}}^{+0.46\mathrm{}}\right(\mathrm{syst})\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$, consistent with solar models.

Solar neutrinos from ${}^8\mathrm{B}$ decay have been detected at the Sudbury Neutrino Observatory via the charged current (CC) reaction on deuterium and the elastic scattering (ES) of electrons. The flux of ${\nu }_e$’s is measured by the CC reaction rate to be ${\phi }^{\mathrm{CC}}\left({\nu }_e\right)=1.75\mathrm{}\pm 0.07\left(\mathrm{stat}{)}_{-0.11\mathrm{}}^{+0.12\mathrm{}}\right(\mathrm{syst})\pm 0.05(\mathrm{theor})\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$. Comparison of ${\phi }^{\mathrm{CC}}\left({\nu }_e\right)$ to the Super-Kamiokande Collaboration’s precision value of the flux inferred from the ES reaction yields a $3.3\sigma$ difference, assuming the systematic uncertainties are normally distributed, providing evidence of an active non- ${\nu }_e$ component in the solar flux. The total flux of active ${}^8\mathrm{B}$ neutrinos is determined to be $5.44\pm 0.99\times {10}^6{\mathrm{cm}}^{-2\mathrm{}}{\mathrm{s}}^{-1\mathrm{}}$.

The Sudbury Neutrino Observatory (SNO) has measured day and night solar neutrino energy spectra and rates. For charged current events, assuming an undistorted ${}^8\mathrm{B}$ spectrum, the night minus day rate is $14.0\%\pm 6.3{\%}_{-1.4\mathrm{}}^{+1.5\mathrm{}}\%$ of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the ${\nu }_e$ asymmetry is found to be $7.0\%\pm 4.9{\%}_{-1.2\mathrm{}}^{+1.3\mathrm{}}\%$. A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the large mixing angle solution.

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.

Results are reported on the measurement of the atmospheric neutrino-induced muon flux at a depth of 2 kilometers below the Earth’s surface from 1229 days of operation of the Sudbury Neutrino Observatory (SNO). By measuring the flux of through-going muons as a function of zenith angle, the SNO experiment can distinguish between the oscillated and unoscillated portion of the neutrino flux. A total of 514 muonlike events are measured between $-1\le \cos {\theta }_{\mathrm{zenith}}\le 0.4$ in a total exposure of $2.30\times {10}^{14}{\mathrm{cm}}^2\mathrm{s}$. The measured flux normalization is $1.22\pm 0.09$ times the Bartol three-dimensional flux prediction. This is the first measurement of the neutrino-induced flux where neutrino oscillations are minimized. The zenith distribution is consistent with previously measured atmospheric neutrino oscillation parameters. The cosmic ray muon flux at SNO with zenith angle $\cos {\theta }_{\mathrm{zenith}}>0.4$ is measured to be $(3.31\pm 0.01(\mathrm{stat})\pm 0.09(\mathrm{sys}))\times {10}^{-10}\mu /\mathrm{s}/{\mathrm{cm}}^2$.