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

Study of solar and other unknown anti-neutrino fluxes with Borexino at LNGS
Physics Letters B Volume 696, Issue 3,
31 January 2011, Pages 191-196
doi:10.1016/j.physletb.2010.12.030
(local copy,  preprint on arXiv)

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 β decay reaction in a large liquid organic scintillator target.  We set a new upper limit for a hypothetical solar flux of 760cm⁻²s⁻¹, obtained assuming an undistorted solar ⁸B energy spectrum.  This corresponds to a limit on the transition probability of solar neutrinos to anti-neutrinos of 1.3×10⁻⁴ (90% C.L.) for E>1.8MeV, covering the entire ⁸B 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.