The Sudbury Neutrino Observatory (SNO) used an array of ${}^3\mathrm{He}$ proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (${\nu }_x$) ${}^8\mathrm{B}$ solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be ${5.54}_{-0.31}^{+0.33}(\mathrm{\text{stat}}{)}_{-0.34}^{+0.36}(\mathrm{\text{syst}})\times {10}^6{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields $\Delta m^2={7.59}_{-0.21}^{+0.19}\times {10}^{-5}{\mathrm{eV}}^2$ and $\theta ={34.4}_{-1.2}^{+1.3}$ degrees. The uncertainty on the mixing angle has been reduced from SNO’s previous results.

• Received 5 June 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.111301