Results from one thousand days of real-time, directional solar-neutrino data

Abstract

A data sample of 1040 days from the Kamiokande II detector, consisting of subsamples of 450 days at electron-energy threshold E e > 9.3 MeV and 590 days at E e > 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 8 B by fusion in the Sun. The measured flux of 8 B 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.PACS numbers: 96.60. Kx, 95.85.Qx, 96.40.Tv A primary motivation of the study of solar neutrinos is the prospect that it will directly reveal the inner structure of the Sun. At the same time, it may also reveal as yet undetected intrinsic properties of neutrinos, owing to the wide range of matter density, the very long distance from the Sun to the Earth, and the relatively high magnetic field traversed by low-energy solar neutrinos in their passage from the center of the Sun to a detector on Earth.In a previous paper, x we describe the observation of 8 B solar neutrinos during an exposure of 450 live days of the detector Kamiokande II in the time period January 1987 through May 1988. The principal result of that observation was a measurement of the value of the 8 B solarneutrino flux relative to that predicted by the standard solar model (SSM), 2 to wit, 0.46 ± 0.13(stat) ±0.08(syst), for observed recoil-electron total energies of E e >93MeV. The neutrino signal was correlated with the direction from the Sun, and the shape of the differential total-energy spectrum was consistent with that predicted from the product of the 8 B decay spectrum 3 and the cross section a(v e e-* v e e), which is the reaction for detecting low-energy v e in Kamiokande II.Here we report the data from an additional 590 live detector days in the period June 1988 through April 1990, obtained with a lower background level due to improved detector performance and reduction of the radioisotopes (primarily 222 Rn) present in the detector water. These improvements permitted a lower electronenergy threshold of 7.5 MeV to be used. The data so obtained, in conjunction with the earlier 450-day data sample, are of particular interest, because they extend over a 1040-day period in which the sunspot activity 4 has risen steeply from a minimum value at the end of solar magnetic cycle 21 to a maximum value approximately 15 times larger at the present peak of solar cycle 22. Ac-

A scintillator purification system for the Borexino solar neutrino detector

“…The standard solar model predicts the flux of 862-keV 7 Be solar neutrinos at the earth's surface be ~ 4.3 x 10 9 /cm 2 /s. That flux produces about 0.5 events/day per ton scintillator from the 7 Be neutrino-electron scattering [27][28][29] .…”

“…Particles scattered by neutrinos with energies below 1 MeV do not produce enough Čerenkov light to measure the 7 Be , pep and pp neutrino fluxes. The Borexino experiment employs a liquid scintillator for detection of these low energy neutrinos by elastic scattering of neutrinos on electrons.…”

“…The mono-energetic 0.862 MeV 7 Be solar neutrino is of particular interest for understanding nuclear reactions in the sun and for understanding neutrino oscillations. Particles scattered by neutrinos with energies below 1 MeV do not produce enough Čerenkov light to measure the 7 Be , pep and pp neutrino fluxes.…”

“…The Kamiokande experiment was the first to achieve real time detection of solar neutrinos [7][8][9] . Kamiokande, and the follow-up Super Kamiokande experiment, measured the flux of the high energy 8 B neutrinos by detecting the Čerenkov radiation produced by electrons scattered by neutrinos.…”

Attempt at Neutrino Detection by Resonance-Type Electrochemical Detector with a Small Size

“…As a result, neutrinos rarely interact with other substances. This property makes neutrinos extremely hard to be detected, and detection of neutrinos needs largesized measurement system like Homestake and Kamiokande experiments 3), 4) . The potential type of V-A and the coupling constant characterize the weak interaction.…”