Search for long-lived particles using displaced vertices of oppositely charged leptons in 140fb-1 of pp collisions at root s = 13 TeV with the ATLAS detector

A search is presented for long-lived particles decaying into an oppositely charged lepton pair, mu+ mu−, e+e−, or e+- μ-+, that form a vertex within the inner tracking system of the ATLAS detector at the Large Hadron Collider, displaced from the primary proton–proton interaction region. The analysis uses the 140 fb-1 of Run-2 data collected at root s = 13 TeV by the ATLAS experiment in 2015-2018. The results of the analysis are interpreted in the context of three benchmark models covering masses from 0.1 to 2.2 TeV and a range of mean proper lifetimes times the speed of light from 1 to 10 000 mm. The first model is a generic Z' boson pair-produced by a new heavy scalar, with the Z' decaying into lepton pairs. The remaining two models are R -parity violating supersymmetric models in which the lightest neutralino chi^tilde_1^0 decays into l+ l'- nu (l,l' = e, mu). The models differ by the mode of production of the chi^tilde_1^0, which can be produced via the decay of pairs of gluinos or of pairs of charginos and neutralinos (chi^tilde_1^+- chi^tilde_1^0, chi^tilde_1^+- chi^tilde_2^0, or chi^tilde_2^0 chi^tilde_1^0). Although each benchmark sample includes pair-produced LLPs, only a single vertex is required to be reconstructed. No dilepton displaced vertex candidate is observed and the results are presented as upper limits on the production cross-sections. This analysis sets leading limits on the production cross-sections for multiple models, including parameter space that has never been directly probed.