Revision of the LHCb Limit on Majorana Neutrinos

TL;DR

This paper revises the LHCb limits on Majorana neutrinos in the 250-5000 MeV range, correcting the decay model used and providing updated formulas for future research.

Contribution

It introduces a revised decay model for Majorana neutrinos, correcting previous theoretical assumptions and offering formulas for more accurate future analyses.

Findings

Corrected the decay model used in LHCb analyses.

Provided new formulas for Majorana neutrino decay rates.

Updated constraints on the mixing angle Vμ4.

Abstract

We revisit the recent limits from LHCb on a Majorana neutrino N in the mass range 250 - 5000 MeV. These limits are among the best currently available, and they will be improved soon by the addition of data from Run 2 of the LHC. LHCb presented a model-independent constraint on the rate of like-sign leptonic decays, and then derived a constraint on the mixing angle V{\mu}4 based on a theoretical model for the B decay width to N and the N lifetime. The model used is unfortunately unsound. We revise the conclusions of the paper based on a decay model similar to the one used for the tau lepton and provide formulae useful for future analyses.