Neutrino Observations from the Sudbury Neutrino Observatory

Abstract

The Sudbury Neutrino Observatory (SNO) is a water imaging Cherenkov detector. Its usage of 1000 metric tons of D$_{2}$O as target allows the SNO detector to make a solar-model independent test of the neutrino oscillation hypothesis by simultaneously measuring the solar $ν_{e}$ flux and the total flux of all active neutrino species. Solar neutrinos from the decay of $^{8}$B have been detected at SNO by the charged-current (CC) interaction on the deuteron and by the elastic scattering (ES) of electrons. While the CC reaction is sensitive exclusively to $ν_{e}$, the ES reaction also has a small sensitivity to $ν_μ$ and $ν_τ$. In this paper, recent solar neutrino results from the SNO experiment are presented. It is demonstrated that the solar flux from $^{8}$B decay as measured from the ES reaction rate under the no-oscillation assumption is consistent with the high precision ES measurement by the Super-Kamiokande experiment. The $ν_{e}$ flux deduced from the CC reaction rate in SNO differs from the Super-Kamiokande ES results by 3.3$sigma$. This is evidence for an active neutrino component, in additional to $ν_{e}$, in the solar neutrino flux. These results also allow the first experimental determination of the total active $^{8}$B neutrino flux from the Sun, and is found to be in good agreement with solar model predictions.