Precision Measurement of the (7)Be Solar Neutrino Interaction Rate in Borexino
A direct measurement of the 0.862 MeV 7Be solar neutrino interaction rate performed with the Borexino detector at the Laboratori Nazionali del Gran Sasso yields 46.0±1.5stat+1.6−1.5syst counts/day/(100 tons). Our result is the first direct measurement of a sub-MeV solar neutrino rate with an accuracy better than 5%. The hypothesis of no oscillation for 7Be solar neutrinos is rejected at 4.9σ C.L. Using the latest Standard Solar Model (SSM) flux predictions, the result leads directly to a precise determination of the survival probability for solar νe's in vacuum, and permits us to probe with unprecedented sensitivity the transition between the matter-enhanced and vacuum-dominated neutrino oscillation regimes characteristic of the MSW-LMA solution to the solar neutrino problem.
Borexino Collaboration Bellini, Gianpaolo Peña Garay, Carlos 2011 Precision Measurement of the (7)Be Solar Neutrino Interaction Rate in Borexino Physical Review Letters 107 14 141302