Direct Measurement of the 7Be Solar Neutrino Flux with 192 Days of Borexino Data

Direct Measurement of the ⁷Be Solar Neutrino Flux with 192 Days of Borexino Data
C. Arpesella et al. (Borexino Collaboration)
Phys. Rev. Lett. 101, 091302 – Published 29 August 2008
doi:10.1103/PhysRevLett.101.091302
(local copy; preprint on arXiv)

Abstract

We report the direct measurement of the ⁷Be solar neutrino signal rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso. The interaction rate of the 0.862 MeV ⁷Be neutrinos is 49 ±3_stat ±4_syst counts/(day⋅100 ton). The hypothesis of no oscillation for ⁷Be solar neutrinos is inconsistent with our measurement at the 4σ C.L. Our result is the first direct measurement of the survival probability for solar ν_e in the transition region between matter-enhanced and vacuum-driven oscillations. The measurement improves the experimental determination of the flux of ⁷Be, pp and CNO solar ν_e, and the limit on the effective neutrino magnetic moment using solar neutrinos.