Measurement of the solar 8B neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector
G. Bellini et al. (Borexino Collaboration)
Phys. Rev. D 82, 033006 – Published 5 August 2010
doi:10.1103/PhysRevD.82.033006
(local copy; preprint on arXiv)
Abstract
We report the measurement of ν−e elastic scattering from 8B solar neutrinos with 3 MeV energy threshold by the Borexino detector in Gran Sasso (Italy). The rate of solar neutrino-induced electron scattering events above this energy in Borexino is 0.22 ±0.04(stat) ±0.01(syst) cpd/100 t, which corresponds to Φ
= 2.4 ±0.4 ±0.1 × 106 cm−2 s−1, in good agreement with measurements from SNO and SuperKamiokaNDE. Assuming the 8B neutrino flux predicted by the high metallicity standard solar model, the average 8B νe survival probability above 3 MeV is measured to be 0.29±0.10. The survival probabilities for 7Be and 8B neutrinos as measured by Borexino differ by 1.9 σ. These results are consistent with the prediction of the MSW-LMA solution of a transition in the solar νe survival probability Pee between the low-energy vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation regimes.