Solar Neutrino Results from Super-Kamiokand

Andrew Renshaw
(UC Irvine)


Super-Kamiokande-IV data taking began in September of 2008, and with upgraded electronics and improvements to water system dynamics, calibration and analysis techniques, a clear solar neutrino signal could be extracted at recoil electron kinetic energies as low as 3.49 MeV. The SK-I through IV extracted solar neutrino flux between 3.49 and 19.49 MeV is found to be (2.37±0.02(stat.)±0.04(syst.))×10^6 /(cm^2sec). A maximum likelihood fit to the amplitude of the expected solar zenith angle variation of the elastic neutrino-electron scattering rate in SK, results in a day/night asymmetry of (-3.2±1.1(stat)±0.5(syst))%. The 2.7 σ significance of a non-zero asymmetry is the first indication of the regeneration of electron type solar neutrinos as they travel through Earth’s matter. An oscillations analysis of SK solar neutrino data measures the solar mixing angle to sin^2(θ_{12})=0.341+0.029-0.025 and the solar neutrino mass splitting to ∆m^2 =4.8+1.80-0.9 ×10^(−5) eV^2.