Measurement of the solar 8B neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector

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 ν_e 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 P_ee between the low-energy vacuum-driven and the high-energy matter-enhanced solar neutrino oscillation regimes.