Resurgence of $Z'$ from the single electron-muon event at ATLAS

Abstract

Inspired by the recent single $e^{\pm}\mu^{\mp}$ event at 2.1 TeV invariant mass from the ATLAS at $\sqrt{s}=13$ TeV with 3.2 fb$^{-1}$ luminosity, we propose an explanation using a $Z'$ gauge boson, which possesses lepton-flavor-changing neutral currents originated from non-universal couplings to charged leptons. We assume that the left-handed charged-lepton mixing matrix equals to the PMNS matrix and no mixing in the neutrino sector to make this phenomenological $Z'$ model more predictive. There are indeed some parameter regions, where the $Z'$ can generate a large enough $e^{\pm}\mu^{\mp}$ production cross section, while at the same time satisfies various observables from lepton-flavor violation and other constraints from the LHC.