A search for an unexpected asymmetry in the production of e + μ − and e − μ + pairs in proton–proton collisions recorded by the ATLAS detector at √ s = 13 TeV

This search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for e + μ − and e − μ + pairs to constrain physics processes beyond the Standard Model. It uses 139 fb − 1 of proton–proton collision data recorded at √ s = 13TeV at the LHC. Targeting sources of new physics which prefer final states containing e + μ − to e − μ + , the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640GeV in a model in which the only other light sparticle is a neutralino when the R -parity-violating coupling λ (cid:3) 231 is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880GeV when g eu 1R = g μ c 1R = 1, at 95% confidence level. The limit on the coupling reduces to g eu 1R = g μ c 1R = 0 . 46 for a mass of 1420GeV.