Electron energy spectra, fluxes, and day-night asymmetries of8B solar neutrinos from measurements with NaCl dissolved in the heavy-water detector at the Sudbury Neutrino Observatory

Abstract

Results are reported from the complete salt phase of the Sudbury Neutrino Observatory experiment in which NaCl was dissolved in the $^{2}\mathrm{H}$${}_{2}\text{O}$ (``${\text{D}}_{2}\text{O}$'') target. The addition of salt enhanced the signal from neutron capture as compared to the pure ${\text{D}}_{2}\text{O}$ 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 ${10}^{6}{\text{cm}}^{\ensuremath{-}2}{\text{s}}^{\ensuremath{-}1}$, the total flux of active-flavor neutrinos from $^{8}\mathrm{B}$ decay in the Sun is found to be ${4.94}_{\ensuremath{-}0.21}^{+0.21}{\text{(stat)}}_{\ensuremath{-}0.34}^{+0.38}\text{(syst)}$ and the integral flux of electron neutrinos for an undistorted $^{8}\mathrm{B}$ spectrum is ${1.68}_{\ensuremath{-}0.06}^{+0.06}{\text{(stat)}}_{\ensuremath{-}0.09}^{+0.08}\text{(syst)}$; the signal from (${\ensuremath{\nu}}_{x},e$) elastic scattering is equivalent to an electron-neutrino flux of ${2.35}_{\ensuremath{-}0.22}^{+0.22}{\text{(stat)}}_{\ensuremath{-}0.15}^{+0.15}\text{(syst)}$. 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 $\ensuremath{\Delta}{m}^{2}=({8.0}_{\ensuremath{-}0.4}^{+0.6})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ eV${}^{2}$ and $\ensuremath{\theta}=33.{9}_{\ensuremath{-}2.2}^{+2.4}$ degrees.