Search for lepton-flavor violation in different-flavor, high-mass final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

TL;DR

This paper searches for heavy particles causing lepton-flavor violation in high-mass dilepton final states at 13 TeV with the ATLAS detector, setting new limits on possible new physics models without observing any excess.

Contribution

It provides the first search for heavy particles decaying into different-flavor dileptons at 13 TeV and sets the most stringent limits to date on related new physics models.

Findings

No significant excess observed over Standard Model predictions.

95% credibility level lower limits set on $Z'$ boson and sneutrino masses.

Upper limits on couplings are more stringent than low-energy experiment limits.

Abstract

A search is performed for a heavy particle decaying into different-flavor, dilepton pairs ($e\mu$, $e\tau$ or $\mu\tau$), using 36.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV collected in 2015-2016 by the ATLAS detector at the Large Hadron Collider. No excesses over the Standard Model predictions are observed. Bayesian lower limits at the 95% credibility level are placed on the mass of a $Z^{\prime}$ boson, the mass of a supersymmetric $\tau$-sneutrino, and on the threshold mass for quantum black-hole production. For the $Z^{\prime}$ and sneutrino models, upper cross-section limits are converted to upper limits on couplings, which are compared with similar limits from low-energy experiments and which are more stringent for the $e\tau$ and $\mu\tau$ modes