REAL-TIME, DIRECTIONAL MEASUREMENT OF B-8 SOLAR NEUTRINOS IN THE KAMIOKANDE-II DETECTOR

The method of B-8 solar-neutrino measurement by means of the reaction nu-ee --> nu-ee in the Kamiokande II detector is described in detail. A data sample of 1040 live detector days in the time period January 1987 through April 1990 yields a clear directional correlation of the solar-neutrino-induced electron events with respect to the Sun and a measurement of the differential electron energy distribution. The measured flux of B-8 solar neutrinos from the subsamples of 450 days at electron energy threshold E(e) greater-than-or-equal-to 9.3 MeV, and 590 days at E(e) greater-than-or-equal-to 7.5 MeV relative to calculations of the B-8 flux based on the standard solar model are 0.46 +/- 0.05(stat) +/- 0.06(syst) times the prediction of Bahcall and Ulrich, and 0.70 +/- 0.08(stat) +/- 0.09(syst) times the prediction of Turck-Chieze et al. The shape of the recoil electron energy distribution is consistent with that expected from the product of the known shape of the neutrino flux from B-8 beta-decay and the cross section for nu-ee --> nu-ee scattering. Within the statistical error, there is no evidence in the solar-neutrino signal for a significant time variation.