Precision measurement of the 7Be solar neutrino interaction rate in Borexino

TL;DR

This paper reports a highly precise direct measurement of the 7Be solar neutrino interaction rate using Borexino, confirming neutrino oscillations and providing insights into the transition between matter-enhanced and vacuum oscillations.

Contribution

It presents the first sub-5% accuracy direct measurement of 7Be solar neutrinos and explores neutrino oscillation regimes with unprecedented sensitivity.

Findings

Measured 7Be neutrino rate at 46.0±1.5(stat)±1.6(syst) counts/day/100 tons

Rejected no-oscillation hypothesis at 4.9σ confidence level

Provided a precise survival probability of solar ν_e in vacuum

Abstract

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$\pm1.5_{\rm stat}$$^{+1.6}_{-1.5\,\rm syst}$ 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 4.9$\sigma$ 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 $\nu_e$'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.