2013/07/14 by Sekiya, Hiroyuki
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Solar and Stellar Astrophysics (astro-ph.SR)
paper · doi:10.48550/arxiv.1307.3686
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 3.5 MeV. The SK-IV extracted solar neutrino flux between 3.5 and 19.5 MeV is found to be (2.36±0.02(stat.)±0.04(syst.))× 106 /(cm2sec). The SK combined recoil electron energy spectrum favors distortions predicted by standard neutrino flavour oscillation parameters over a flat suppression at 1σ level. 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 non-zero asymmetry is the first indication of the regeneration of electron type solar neutrinos as they travel through Earth's matter. A fit to all solar neutrino data and KamLAND yields sin2 θ12 = 0.304 ± 0.013, sin2 θ13 = 0.031+0.017-0.015 and Δm221 = 7.45+0.20-0.19 × 10-5 \rm eV2.