Study of solar and other unknown anti-neutrino fluxes with Borexino at LNGS

TL;DR

This study uses the Borexino detector to search for unknown anti-neutrino fluxes, setting new upper limits on solar anti-neutrinos and providing constraints on unknown sources in the 1.8 to 17.8 MeV energy range.

Contribution

It presents the first stringent upper limits on solar anti-neutrino fluxes and unknown anti-neutrino sources using Borexino data, improving previous constraints.

Findings

Set a new upper limit for solar anti-neutrino flux of 760 cm^{-2}s^{-1}

Constrained the transition probability of solar neutrinos to anti-neutrinos to 1.3×10^{-4}

Provided differential limits on anti-neutrino fluxes from unknown sources between 1.8 and 17.8 MeV

Abstract

We report on the search for anti-neutrinos of yet unknown origin with the Borexino detector at the Laboratori Nazionali del Gran Sasso. In particular, a hypothetical anti-neutrino flux from the Sun is investigated. Anti-neutrinos are detected through the neutron inverse $\beta$ decay reaction in a large liquid organic scintillator target. We set a new upper limit for a hypothetical solar $\bar{\nu}_e$ flux of 760 ${\rm cm}^{-2}{\rm s}^{-1}$, obtained assuming an undistorted solar $^8$B energy spectrum. This corresponds to a limit on the transition probability of solar neutrinos to anti-neutrinos of $1.3\times10^{-4}$ (90\% C.L.) for $E_{\bar{\nu}}>1.8$ MeV, covering the entire $^{8}$B spectrum. Best differential limits on anti-neutrino fluxes from unknown sources are also obtained between the detection energy threshold of 1.8 MeV and 17.8 MeV with more than 2 years of data.