Search for long-lived particles decaying to $e^\pm \mu^\mp \nu$

TL;DR

This paper searches for long-lived particles decaying into electron-muon-neutrino final states within a specific mass and lifetime range, using LHCb data, but finds no evidence and sets upper limits on production rates.

Contribution

First search for long-lived particles decaying to $e^   u$ in the specified mass and lifetime range using displaced vertex analysis at LHCb.

Findings

No evidence of long-lived particles was observed.

Upper limits on production cross-section times branching fraction were established.

The analysis constrains models predicting such long-lived particles.

Abstract

Long-lived particles decaying to $e^\pm \mu^\mp \nu$, with masses between 7 and $50$ GeV/c$^2$ and lifetimes between 2 and $50$ ps, are searched for by looking at displaced vertices containing electrons and muons of opposite charges. The search is performed using $5.4$ fb$^{-1}$ of $pp$ collisions collected with the LHCb detector at a centre-of-mass energy of $\sqrt{s} = 13$ TeV. Three mechanisms of production of long-lived particles are considered: the direct pair production from quark interactions, the pair production from the decay of a Standard-Model-like Higgs boson with a mass of $125$ GeV/c$^2$, and the charged current production from an on-shell $W$ boson with an additional lepton. No evidence of these long-lived states is obtained and upper limits on the production cross-section times branching fraction are set on the different production modes.