Probing neutrino magnetic moment and unparticle interactions with Borexino

TL;DR

This paper uses Borexino data to set new limits on the neutrino magnetic moment and unparticle interactions, improving previous bounds and demonstrating the experiment's sensitivity to these rare phenomena.

Contribution

It provides the first Borexino-based constraints on neutrino magnetic moments and unparticle couplings, with significant improvements over prior limits.

Findings

Limit on solar neutrino magnetic moment: μ_ν < 8.4×10^−11 μ_B at 90% CL

Enhanced the upper limit on ν_τ magnetic moment by three orders of magnitude

Set new bounds on neutrino-unparticle coupling constants

Abstract

We discuss the limits on the neutrino magnetic moment and hypothetical interactions with a hidden unparticle sector, coming from the first neutrino data release of the Borexino experiment. The observed spectrum in Borexino depends weakly on the solar model used in the analysis, since most of the signal comes from the mono-energetic 7Be neutrinos. This fact allows us to calibrate the nu-e scattering cross section through the spectral shape. In this way, we have derived a limit on the magnetic moment for the neutrinos coming from the Sun (in which a nu_mu and nu_tau component is present): mu_nu<8.4E-11 mu_B (90%CL) which is comparable with those obtained from low energy reactor experiments. Moreover, we improve the previous upper limit on magnetic moment of the nu_tau by three orders of magnitude and the limit on the coupling constant of the neutrino with a hidden unparticle sector.