Search for type-III seesaw heavy leptons in dilepton final states in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

TL;DR

This paper reports a search for type-III seesaw heavy leptons in dilepton final states using 13 TeV proton-proton collision data from the ATLAS detector, setting new exclusion limits on their masses.

Contribution

The study provides the first comprehensive search for type-III seesaw heavy leptons at 13 TeV with the ATLAS detector, establishing new mass exclusion limits.

Findings

No significant excess over the Standard Model was observed.

The lower mass limit for type-III seesaw heavy leptons is set at 790 GeV.

The analysis constrains models predicting heavy leptons in the type-III seesaw mechanism.

Abstract

A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to 139 fb$^{-1}$ of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on the final state with two light leptons (electrons or muons) of different flavour and charge combinations, with at least two jets and large missing transverse momentum. No significant excess over the Standard Model expectation is observed. The results are translated into exclusion limits on heavy-lepton masses, and the observed lower limit on the mass of the type-III seesaw heavy leptons is 790 GeV at 95% confidence level.