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 = 13 TeV 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 640 GeV in a model in which the only other light sparticle is a neutralino when the R- parity-violating coupling λ′ 231 is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when geu 1R = gμc 1R = 1, at 95% confidence level. The limit on the coupling reduces to geu 1R = gμc 1R = 0.46 for a mass of 1420 GeV.

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

G. L. Alberghi;F. Alfonsi;E. Ballabene;L. Bellagamba;M. Bindi;D. Boscherini;G. Cabras;D. Caforio;G. Carratta;N. Cavalli;L. Clissa;S. De Castro;L. Fabbri;M. Franchini;A. Gabrielli;B. Giacobbe;F. Lasagni Manghi;L. Massa;A. Polini;L. Rinaldi;