Solar Neutrino Observations at the Sudbury Neutrino Observatory

Abstract

The Sudbury Neutrino Observatory (SNO) is a 1000-tonne heavy water Cherenkov detector. Its usage of \dto as target allows the simultaneous measurements of the ${\nu }_e$ flux from ${}^8$B decay in the Sun and the total flux of all active neutrino species through the charged-current and the neutral-current interactions on the deuterons. Assuming the standard ${}^8$B shape, the ${\nu }_e$ component of the ${}^8$B solar neutrino flux is measured to be ${\varphi }_e=1.76_{-0.05}^{+0.05}{(stat.)}_{-0.09}^{+0.09}(syst.)x10^6{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$ for a kinetic energy threshold of 5 MeV. The non-\nue component is found to be $\phinumutau = 3.41^{+0.45}_{-0.45}{(stat.)}^{+0.48}_{-0.45} {(syst.)} x 10^6 {\rm cm}^{-2} {\rm s}^{-1}$. This $5.3\sigma$ difference provides strong evidence for ${\nu }_e$ flavor transformation in the solar neutrino sector. The total active neutrino flux is measured with the neutral-current reaction at a neutrino energy threshold of 2.2 MeV. This flux is determined to be ${\varphi }_{NC}=5.09_{-0.43}^{+0.44}{(stat.)}_{-0.43}^{+0.46}(syst.)x10^6{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, and is consistent with solar model predictions. Assuming an undistorted ${}^8$B spectrum, the night minus day rate is 14.0$\pm$6.3(stat.)${}_{-1.4}^{+1.5}$(sys.)\% of the average rate in the charged-current channel. If the total active neutrino flux is constrained to have no asymmetry, the night-day asymmetry in the ${\nu }_e$ flux is found to be 7.0$\pm$4.9(stat.)${}_{1.2}^{+1.3}$(sys.)\%. A global analysis of all the available solar neutrino data in terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution.

invited talk at the SLAC Summer Institute Topical Conference (SSI02-TTh01), 2002, 43 pages, 19 figures, 10 tables