Results from the Neutral Current Detector phase of the Sudbury Neutrino Observatory

Abstract

The Sudbury Neutrino Observatory (SNO) was a heavy water Cerenkov detector designed to solve the long-standing ``solar neutrino problem''; a discrepancy between the measured and predicted flux of electron-flavour solar neutrinos. SNO measured the rate of charged-current and neutral-current reactions of neutrinos in heavy water and was able to demonstrate that neutrinos from the Sun, produced in the electron flavour eigenstate, undergo flavour change on their way to the Earth, thus resolving the solar neutrino problem. The experiment was conducted in three phases, differing by the method for measuring the neutral current rate. This short paper summarizes results from the third phase of the experiment, which used an array of 36 strings of proportional counters filled with $^3$He to detect neutrons from the neutral-current reaction. When the data from the three phases is combined with solar and the KamLAND neutrino oscillation experiments, the resulting limits on the solar neutrino mixing angle and mass-squared difference are $\theta_{12} = 34.4^{+1.3}_{-1.2}$ degrees and $\Delta m_{12}^2 =7.59^{+0.19}_{-0.21}\times 10^{-5}$eV$^2$, respectively.