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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"><mml:msqrt><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msqrt><mml:mo linebreak="goodbreak" linebreakstyle="after">=</mml:mo><mml:mn>13</mml:mn></mml:math> TeV

This search, a type not previously performed at ATLAS, uses comparison of the production cross sections for e+μ− and e−μ+ pairs to constrain physics processes beyond Standard Model. It 139fb−1 proton–proton collision data recorded s=13 TeV LHC. Targeting sources new which prefer final states containing e−μ+, search contains two broad signal regions are used provide model-independent constraints on ratio 2% level. The also has special selections targeting supersymmetric models leptoquark signatures. Observations using one these able exclude, 95% confidence level, singly produced smuons with masses up 640 GeV in model only other light sparticle is neutralino when R-parity-violating coupling λ231′ close unity. selection exclude scalar leptoquarks below 1880 g1Reu=g1Rμc=1, limit reduces g1Reu=g1Rμc=0.46 mass 1420 GeV.