Precise Measurement of Solar Neutrinos with Super-Kamiokande III

New solar neutrino measurements with the Super-Kamiokande detector are reported. The main motivation of this thesis is to observe the spectrum distortion of solar neutrinos caused by the matter effect of neutrino oscillation in the Sun (MSW effect). The data for this thesis were taken between August 2006 and August 2008, during the third phase of Super-Kamiokande (SK-III). Two neutrino samples are used in this thesis. The first one with total electron energy between 6.5 and 20MeV has a total livetime of 547.9 days. The second, with total electron energy between 4.5 and 6.5MeV has a total livetime of 298.2 days after rejecting high background periods caused by radioactive impurities accidentally injected into the detector. With improved detector calibrations, a full detector simulation, and analysis methods, the systematic uncertainty on the total neutrino flux is estimated to be ±2.3%, which is about two thirds of the systematic uncertainty in the first phase of Super-Kamiokande (SK-I). The observed 8B solar flux in the 5.0 to 20MeV electron energy region is 2.28 ± 0.04 (stat.) ± 0.05 (sys.) ×106cm−2sec−1, in agreement with previous measurements. The day-night asymmetry is measured to be ADN = −0.057 ± 0.031(stat.)±0.013(sys.). In the 4.5-5.0 MeV region, the observed flux is 2.14 +0.56 −0.54 (stat) ×106cm−2sec−1 and is consistent with the flux in the 5.0-20MeV region. A global oscillation analysis is carried out using SK-I, II, and III, and is combined with the results of other solar neutrino experiments. The best-fit oscillation parameters are obtained with the world’s best accuracy as sin 2 θ12 = 0.29 +0.024 −0.011 and ∆m2 12 = 6.03+1.21 −1.67 × 10−5 eV 2. Combined with KamLAND result, the best-fit oscillation parameters are found to be sin2 θ12 = 0.304 +0.017