Solar neutrino physics with Borexino I

TL;DR

Borexino's phase I provided precise real-time measurements of solar neutrinos, confirming key oscillation parameters and detecting specific neutrino fluxes, advancing understanding of solar neutrino physics.

Contribution

This paper reports the first real-time measurement of $^{7}$Be solar neutrinos with high accuracy and confirms the MSW-LMA oscillation solution without assuming CPT invariance.

Findings

Measured $^{7}$Be neutrino interaction rate with better than 5% accuracy

Confirmed absence of day-night asymmetry in solar neutrinos with 1.4% precision

Detected $pep$ solar neutrino signal and constrained CNO neutrino flux

Abstract

Borexino is a large-volume liquid scintillator detector installed in the underground halls of the Laboratori Nazionali del Gran Sasso in Italy. After several years of construction, data taking started in May 2007. The Borexino phase I ended after about three years of data taking. Borexino provided the first real time measurement of the $^{7}$Be solar neutrino interaction rate with accuracy better than 5% and confirmed the absence of its day-night asymmetry with 1.4% precision. This latter Borexino results alone rejects the LOW region of solar neutrino oscillation parameters at more than 8.5 $\sigma$ C.L. Combined with the other solar neutrino data, Borexino measurements isolate the MSW-LMA solution of neutrino oscillations without assuming CPT invariance in the neutrino sector. Borexino has also directly observed solar neutrinos in the 1.0-1.5 MeV energy range, leading to the first direct evidence of the $pep$ solar neutrino signal and the strongest constraint of the CNO solar neutrino flux up to date. Borexino provided the measurement of the solar $^{8}$B neutrino rate with 3 MeV energy threshold.