Search for vector-like leptons coupling to first- and second-generation Standard Model leptons in pp collisions at sqrt(s) = 13 TeV with the ATLAS detector

A search for pair production of vector-like leptons (VLLs) coupling to first- and second-generation Standard Model (SM) leptons is presented. The search is based on a dataset of proton-proton (pp) collisions at a centre-of-mass energy of sqrt(s) =13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider (LHC), corresponding to an integrated luminosity of 140 fb -1. Events are categorised depending on the flavour and multiplicity of leptons (electrons or muons), as well as on the scores of a deep neural network targeting particular signal topologies according to the decay modes of the VLLs. In each of the signal regions, the scalar sum of the transverse momentum of the leptons and the missing transverse momentum (ST) is analysed. The main background processes are estimated using dedicated control regions in a simultaneous fit with the signal regions to data. No significant excess above the Standard Model background expectation is observed. Limits are set at 95% confidence level on the production cross-sections of vector-like electrons and muons as a function of the vector-like lepton mass, separately for SU(2) doublet and singlet scenarios. The resulting mass lower limits are: Doublet Scenario: 1220 GeV for vector-like electrons and 1270 GeV for vector-like muons. Singlet Scenario: 320 GeV for vector-like electrons and 400 GeV for vector-like muons.