Solar neutrino observations at the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) is a 1000-tonne heavy water Cherenkov detector. Its usage of D2O as target allows the simultaneous measurements of the νe flux from B decay in the Sun and the total flux of all active neutrino species through the charged-current and the neutralcurrent interactions on the deuterons. Assuming the standard B shape, the νe component of the B solar neutrino flux is measured to be φe= 1.76 −0.05(stat.) +0.09 −0.09 (syst.)× 10 cms for a kinetic energy threshold of 5 MeV. The non-νecomponent is found to be φμτ= 3.41 +0.45 −0.45(stat.) +0.48 −0.45 (syst.)× 10 cms. This 5.3σ difference provides strong evidence for νe flavor transformation in the solar neutrino sector. The total active neutrino flux is measured with the neutral-current reaction at a neutrino energy threshold of 2.2 MeV. This flux is determined to be φNC= 5.09 +0.44 −0.43(stat.) +0.46 −0.43 (syst.) × 10 cms, and is consistent with solar model predictions. Assuming an undistorted B spectrum, the night minus day rate is 14.0±6.3(stat.) −1.4(sys.)% of the average rate in the charged-current channel. If the total active neutrino flux is constrained to have no asymmetry, the night-day asymmetry in the νe flux is found to be 7.0±4.9(stat.) −1.2(sys.)%. A global analysis of all the available solar neutrino data in terms of matter-enhanced oscillations of two active flavors strongly favors the Large Mixing Angle (LMA) solution. TTH01 XXX SLAC Summer Institute (SSI2002), Stanford, CA, 5-16 August, 2002