Electron energy spectra, fluxes, and day-night asymmetries of B-8 solar neutrinos from measurements with NaCl dissolved in the heavy-water detector at the Sudbury Neutrino Observatory

Results are reported from the complete salt phase of the Sudbury Neutrino Observatory experiment in which NaCl was dissolved in the H22O ("D2O") target. The addition of salt enhanced the signal from neutron capture as compared to the pure D2O detector. By making a statistical separation of charged-current events from other types based on event-isotropy criteria, the effective electron recoil energy spectrum has been extracted. In units of 106cm-2s-1, the total flux of active-flavor neutrinos from B8 decay in the Sun is found to be 4.94-0.21+0.21(stat)-0.34+0.38(syst) and the integral flux of electron neutrinos for an undistorted B8 spectrum is 1.68-0.06+0.06(stat)-0. 09+0.08(syst); the signal from (νx,e) elastic scattering is equivalent to an electron-neutrino flux of 2.35-0.22+0.22(stat)-0.15+0.15(syst). These results are consistent with those expected for neutrino oscillations with the so-called large mixing angle parameters and also with an undistorted spectrum. A search for matter-enhancement effects in the Earth through a possible day-night asymmetry in the charged-current integral rate is consistent with no asymmetry. Including results from other experiments, the best-fit values for two-neutrino mixing parameters are Δm2=(8.0-0.4+0.6)×10-5 eV2 and θ=33.9-2.2+2.4 degrees. © 2005 The American Physical Society.