Low-energy-threshold analysis of the Phase I and Phase II data sets of the Sudbury Neutrino Observatory

Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is Teff=3.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of 10⁶ cm^-2 s^-1, the total flux of active-flavor neutrinos from ⁸B decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the ⁸B neutrino energy spectrum, is found to be ΦNC=5.140_-0.158+0.160(stat)_-0.117+0.132(syst). These uncertainties are more than a factor of 2 smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the Sudbury Neutrino Observatory data in which the free parameters directly describe the total ⁸B neutrino flux and the energy-dependent νₑ survival probability provides a measure of the total ⁸B neutrino flux Φ_⁸B=5.046_-0.152+0.159(stat)_-0.123+0.107(syst). Combining these new results with results of all other solar experiments and the KamLAND reactor experiment yields best-fit values of the mixing parameters of θ₁₂=34.06_-0.84+1.16 degrees and Δm₂₁²=7.59_-0.21+0.20×10^-5 eV². The global value of Φ_⁸B is extracted to a precision of _-2.95+2.38%. In a three-flavor analysis the best fit value of sin²θ₁₃ is 2.00_-1.63+2.09×10^-2. This implies an upper bound of sin²θ₁₃<0.057 ($95%$ C.L.).