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 <math altimg='"si1.svg"'> <msqrt> <mrow> <mi>s</mi> </mrow> </msqrt> <mo linebreak='"goodbreak"' linebreakstyle='"after"'>=</mo> </math>