Abstract
We report on an improved measurement of the B8 solar neutrino interaction rate with the Borexino experiment at the Laboratori Nazionali del Gran Sasso. Neutrinos are detected via their elastic scattering on electrons in a large volume of liquid scintillator. The measured rate of scattered electrons above 3 MeV of energy is 0.223−0.016+0.015(stat) −0.006+0.006(syst) cpd/100 t, which corresponds to an observed solar neutrino flux assuming no neutrino flavor conversion of ΦB8ES=2.57−0.18+0.17(stat) −0.07+0.07(syst)×106 cm−2 s−1. This measurement exploits the active volume of the detector in almost its entirety for the first time, and takes advantage of a reduced radioactive background following the 2011 scintillator purification campaign and of novel analysis tools providing a more precise modeling of the background. Additionally, we set a new limit on the interaction rate of solar hep neutrinos, searched via their elastic scattering on electrons as well as their neutral current-mediated inelastic scattering on carbon, C12(ν,ν′)C*12 (Eγ=15.1 MeV).6 MoreReceived 3 February 2020Accepted 21 February 2020DOI:https://doi.org/10.1103/PhysRevD.101.062001Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasSolar neutrinosParticles & FieldsGravitation, Cosmology & Astrophysics
Highlights
Borexino detects solar neutrinos with the lowest energy threshold of all solar neutrino experiments to date
Results from the HER-II sample use data from the entire active volume, while the HER-I sample requires a spatial cut to remove the top layer of scintillator
This is motivated by the presence of PPO from a scintillator leak, in proximity of the polar region, into the upper buffer fluid volume
Summary
Borexino detects solar neutrinos with the lowest energy threshold of all solar neutrino experiments to date. Borexino has performed a new comprehensive measurement of pp-chain solar neutrinos [1], improving previous results on pp, 7Be, and pep neutrino interaction rates [2,3,4,5], 8B neutrinos above ∼3 MeV [6], and setting a limit on the neutrino flux produced by the 3He-proton fusion (hep). We describe the improved measurement of the 8B solar neutrino interaction rate, performed with a greater than tenfold increase of exposure with respect to an earlier measurement [6] and using an electron energy threshold of ∼3 MeV, the lowest to date.
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