Search for displaced vertices of oppositely charged leptons from decays of long-lived particles in pp collisions at s=13 TeV with the ATLAS detector

Abstract

A search for long-lived particles decaying into an oppositely charged lepton pair, μμ, ee, or eμ, is presented using 32.8fb−1of ppcollision data collected at √s=13TeV by the ATLAS detector at the LHC. Candidate leptons are required to form a vertex, within the inner tracking volume of ATLAS, displaced from the primary ppinteraction region. No lepton pairs with an invariant mass greater than 12GeV are observed, consistent with the background expectations derived from data. The detection efficiencies for generic resonances with lifetimes (cτ) of 100–1000mm decaying into a dilepton pair with masses between 0.1–1.0TeV are presented as a function of pTand decay radius of the resonances to allow the extraction of upper limits on the cross sections for theoretical models. The result is also interpreted in a supersymmetric model in which the lightest neutralino, produced via squark–antisquark production, decays into + −ν( , =e, μ) with a finite lifetime due to the presence of R-parity violating couplings. Cross-section limits are presented for specific squark and neutralino masses. For a 700GeV squark, neutralinos with masses of 50–500GeV and mean proper lifetimes corresponding to cτvalues between 1mm to 6m are excluded. For a 1.6TeV squark, cτvalues between 3mm to 1m are excluded for 1.3TeV neutralinos.