Abstract

A data sample of 1040 days from the Kamiokande II detector, consisting of subsamples of 450 days at electron-energy threshold Ee≥9.3 MeV and 590 days at Ee≥7.5 MeV, 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. These provide unequivocal evidence for the production of B8 by fusion in the Sun. The measured flux of B8 solar neutrinos from the two subsamples relative to a prediction of the standard solar model is 0.46±0.05(stat)±0.06(syst). The total data sample is tested for short-term time variation; within the statistical error, no significant variation is observed.Received 5 June 1990DOI:https://doi.org/10.1103/PhysRevLett.65.1297©1990 American Physical Society