Solar Neutrino Results from the Sudbury Neutrino Observatory

Abstract

We describe here the measurement of the flux of neutrinos created by the decay of solar ^8B by the Sudbury Neutrino Observatory (SNO). The neutrinos were detected via the charged current (CC) reaction on deuterium and by the elastic scattering (ES) of electrons. The CC reaction is sensitive exclusively to $ν_e$'s, while the ES reaction also has a small sensitivity to $ν_μ$'s and $ν_τ$'s. The flux of $ν_e$'s from ^8B decay measured by the CC reaction rate is $ϕ^CC (ν_e) = 1.75 \pm 0.07 (stat.)^{+0.1 2}_{-0.11} (sys.) \pm 0.05 (theor.) \times 10^6 cm^-2 s^-1$. Assuming no flavor transformation, the flux inferred from the ES reaction rate is $ϕ^ES (ν_x)=2.39\pm 0.34 (stat.) ^{+0.16}_{-0.14} (sys.) \times 10^6 cm^-2 s^-1$. Comparison of $ϕ^CC (ν_e)$ to the Super-Kamiokande Collaboration's precision value of $ϕ^ES (ν_x)$ yields a $3.3σ$ difference, assuming the systematic uncertainties are normally distributed, providing evidence that there is a non-electron flavor active neutrino component in the solar flux. The total flux of active ^8B neutrinos is thus determined to be $5.44\pm 0.99 \times 10^6 cm^-2 s^-1$, in close agreement with the predictions of solar models.