Observations of neutral-current ν interactions on deuterium in the Sudbury Neutrino Observatory are reported. Using the neutral current, elastic scattering, and charged current reactions and assuming the standard 8 B shape, the

The Sudbury Neutrino Observatory (SNO) has measured day and night solar neutrino energy spectra and rates. For charged current events, assuming an undistorted 8B spectrum, the night minus day rate is 14.0%+/-6.3%(+1.5%)(-1.4%) 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%+/-4.9%(+1.3%)(-1.2%). A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the large mixing angle solution.

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B. AHARMIM et al.PHYSICAL REVIEW C 75, 045502 (2007) 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 H 2 O (in the following denoted as D 2 O) to the solar 8 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 ν e flux. Under the assumption that the 8 B spectrum is undistorted, the measurements from this phase yield a solar ν e flux of φ(ν e ) = 1.76 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 ν e flux is found to be A e = 7.0 ± 4.9 (stat.) +1.3 −1.2 % (syst.), when the asymmetry in the total flux is constrained to be zero.

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