New limits on heavy sterile neutrino mixing in 8B decay obtained with the Borexino detector

New limits on heavy sterile neutrino mixing in ⁸B decay obtained with the Borexino detector
G. Bellini et al. (Borexino Collaboration)
Phys. Rev. D 88, 072010 – Published 29 October 2013
[doi:10.1103/PhysRevD.88.072010] (preprint on arXiv)

Abstract

If heavy neutrinos with mass mν_H≥2m_e are produced in the Sun via the decay ⁸B→⁸B_e+e⁺+ν_H in a side branch of the pp chain, they would undergo the observable decay into an electron, a positron and a light neutrino ν_H→ν_L+e⁺+e⁻.  In the present work Borexino data are used to set a bound on the existence of such decays.  We constrain the mixing of a heavy neutrino with mass 1.5 MeV≤mν_H≤14 MeV to be |U_eH|²≤(10⁻³−4×10⁻⁶), respectively.  These are tighter limits on the mixing parameters than obtained in previous experiments at nuclear reactors and accelerators.