Neutral current and day night measurements from the pure D2O phase of SNO

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The Sudbury Neutrino Observatory is a 1000 T D2O Cerenkov detector that is sensitive to 8B solar neutrinos. The energy, radius, and direction with respect to the sun is measured for each neutrino event; these distributions are used to separately determine the rates of the charged current, neutral current and electron scattering reactions of neutrinos on deuterium. Assuming an undistorted 8B spectrum, the νe component of the 8B solar flux is φe = 1.76-0.05+0.05 (stat. -0.09+0.09 (syst.) × 106 cm-2s-1 based on events with a measured kinetic energy above 5 MeV. The non-νe component is φμτ = 3.41-0.45+0.45 (stat. -0.45+0.48 (syst.) × 106 cm-2s-1, 5.3σ greater than zero, providing strong evidence for solar νe flavor transformation. The total flux measured with the NC reaction is φNC = 5.09-0.43+0.44(stat. -0.43+0.46 (syst.) × 106 cm-2s-1, consistent with solar models. The night minus day rate is 14.0% ± 6.3%-1.4+1.5% of the average rate. If the total flux of active neutrinos is additionally constrained to have no asymmetry, the νe asymmetry is found to be 7.0% ± 4.9%-1.2+1.3%. A global solar neutrino analysis in terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution.

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Nuclear Physics B - Proceedings Supplements

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