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

A search is presented for long-lived particles decaying into an oppositely charged lepton pair, ⁺ ⁻, ⁺ ⁻, or ^± ^∓, 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 √ = 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 ′ boson pair-produced by a new heavy scalar, with the ′ decaying into lepton pairs. The remaining two models are -parity violating supersymmetric models in which the lightest neutralino ˜⁰₁decays into ℓ⁺ ℓ ′⁻ (ℓ, ℓ′ = , ). The models differ by the mode of production of the ˜⁰₁ , which can be produced via the decay of pairs of gluinos or of pairs of charginos and neutralinos (˜^±₁ ˜⁰₁, ˜^±₁ ˜⁰₂, or ˜⁰₂ ˜⁰₁). 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.