Search for heavy neutral leptons in $W^+\to\mu^{+}\mu^{\pm}\text{jet}$ decays

TL;DR

This paper reports a search for heavy neutrinos produced in W boson decays into two muons and a jet, using LHCb data, setting upper limits on their coupling in the 5-50 GeV/c^2 mass range.

Contribution

It provides the first constraints on heavy neutrino couplings in W decays within the 5-50 GeV/c^2 mass range using LHCb data.

Findings

No excess observed over background expectations.

Upper limits on heavy neutrino coupling are set at 10^{-3} for lepton-number-conserving decays.

Limits are around 10^{-4} for lepton-number-violating decays.

Abstract

A search is performed for heavy neutrinos in the decay of a $W$ boson into two muons and a jet. The data set corresponds to an integrated luminosity of approximately $3.0 \text{ fb}^{-1}$ of proton-proton collision data at centre-of-mass energies of 7 and $8 \text{ TeV}$ collected with the LHCb experiment. Both same-sign and opposite-sign muons in the final state are considered. Data are found to be consistent with the expected background. Upper limits on the coupling of a heavy neutrino with the Standard Model neutrino are set at $95\%$ confidence level in the heavy-neutrino mass range from 5 to $50 \text{ GeV}/c^2$. These are of the order of $10^{-3}$ for lepton-number-conserving decays and of the order of $10^{-4}$ for lepton-number-violating heavy-neutrino decays.