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

TLDR: In this paper, a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory is reported, where the total flux of active-flavor neutrinos from 8B decay in the Sun measured using the neutral current (NC) reaction, with no constraint on the 8B neutrino energy spectrum, is found to be FNC=5.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data.

Abstract: 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 FNC=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 e survival probability provides a measure of the total 8B neutrino flux F8B=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 12=34.06-0.84+1.16 degrees and m212=7.59-0.21+0.2010-5 eV2. The global value of 8B is extracted to a precision of -2.95+2.38%. In a three-flavor analysis the best fit value of sin213 is 2.00-1.63+2.0910-2. This implies an upper bound of sin213<0.057 (95% C.L.).