Search for new phenomena in events with two opposite-charge leptons, jets and missing transverse momentum in pp collisions at $\sqrt{\mathrm{s}}$ = 13 TeV with the ATLAS detector

The collaboration
JHEP 04 (2021) 165, 2021.

Abstract (data abstract)
The results of a search for direct pair production of top squarks and for dark matter in events with two opposite-charge leptons (electrons or muons), jets and missing transverse momentum are reported, using 139~\mbox{fb$$^{-1}$$} of integrated luminosity from proton--proton collisions at $\sqrt{s}=13$ TeV, collected by the ATLAS detector at the Large Hadron Collider during Run~2 (2015--2018). This search considers the pair production of top squarks and is sensitive across a wide range of mass differences between the top squark and the lightest neutralino. Additionally, spin-0 mediator dark-matter models are considered, in which the mediator is produced in association with a pair of top quarks. The mediator subsequently decays to a pair of dark-matter particles. No significant excess of events is observed above the Standard Model background, and limits are set at $95\%$\ confidence level. The results exclude top squark masses up to about $1$ TeV, and masses of the lightest neutralino up to about $500$ GeV. Limits on dark-matter production are set for scalar (pseudoscalar) mediator masses up to about $250~(300)$ GeV.