Electron Energy Spectra, Fluxes, and Day-Night Asymmetries of $^{8}$B Solar Neutrinos from the 391-Day Salt Phase SNO Data Set

摘要

Results are reported from the complete salt phase of the Sudbury NeutrinoObservatory experiment in which NaCl was dissolved in the D$_2$O target. Theaddition of salt enhanced the signal from neutron capture, as compared to thepure D$_2$O detector. By making a statistical separation of charged-currentevents from other types based on event-isotropy criteria, the effectiveelectron recoil energy spectrum has been extracted. In units of $ 10^6$cm$^{-2}$ s$^{-1}$, the total flux of active-flavor neutrinos from $^8$B decayin the Sun is found to be$4.94^{+0.21}_{-0.21}{(stat)}^{+0.38}_{-0.34}{(syst)}$ and the integral flux ofelectron neutrinos for an undistorted $^8$B spectrum is$1.68^{+0.06}_{-0.06}{(stat)}^{+0.08}_{-0.09}{(syst)}$; the signal from($\nu_x$,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 areconsistent with those expected for neutrino oscillations with the so-calledLarge Mixing Angle parameters, and also with an undistorted spectrum. A searchfor matter-enhancement effects in the Earth through a possible day-nightasymmetry in the charged-current integral rate is consistent with no asymmetry.Including results from other experiments, the best-fit values for two-neutrinomixing parameters are $\Delta m^2 = (8.0^{+0.6}_{-0.4}) \times 10^{-5}$ eV$^2$and $\theta = 33.9 ^{+2.4}_{-2.2}$ degrees.