Solar neutrino measurements in Super-Kamiokande-IV

Abstract

Upgraded electronics, improved water system dynamics, better calibration and analysis techniques allowed Super-Kamiokande-IV to clearly observe very low-energy B-8 solar neutrino interactions, with recoil electron kinetic energies as low as similar to 3.5 MeV. Super-Kamiokande-IV data-taking began in September of 2008; this paper includes data until February 2014, a total livetime of 1664 days. The measured solar neutrino flux is (2.308 +/- 0.020)(stat)(-0.040)(+0.039) (syst)) x 10(6)/(cm(2) sec) assuming no oscillations. The observed recoil electron energy spectrum is consistent with no distortions due to neutrino oscillations. An extended maximum likelihood fit to the amplitude of the expected solar zenith angle variation of the neutrino-electron elastic scattering rate in SK-IV results in a day/night asymmetry of (-3.6 +/- 1.6(stat) +/- 0.6(syst)%. The SK-IV solar neutrino data determine the solar mixing angle as sin(2)theta(12) = 0.327(-0.031)(+0.026), all SK solar data (SK-I, SK-II, SK III and SK-IV) measures this angle to be sin(2)theta(12) = 0.334(-0.023)(+0.027), the determined mass-squared splitting is Delta m(21)(2) = 4.8(-0.8)(+1.5) x 10(-5) eV(2).