Search for charged-lepton-flavor violating 𝜇⁢𝜏⁢𝑞⁢𝑡 interactions in top-quark production and decay in 𝑝⁢𝑝 collisions at √𝑠=13 TeV with the ATLAS detector at the LHC

A search for charged-lepton-flavor violating 𝜇⁢𝜏⁢𝑞⁢𝑡 (𝑞=𝑢, 𝑐) interactions is presented, considering both top-quark production and decay. The data analyzed correspond to 140  fb−1 of proton-proton collisions at a center-of-mass energy of √𝑠=13  TeV recorded with the ATLAS detector at the Large Hadron Collider. The analysis targets events containing two muons with the same electric charge, a hadronically decaying 𝜏-lepton and at least one jet, with exactly one 𝑏-tagged jet, produced by a 𝜇⁢𝜏⁢𝑞⁢𝑡 interaction. Agreement with the Standard Model expectation within 1.6 standard deviations is observed, and limits are set at the 95% confidence level (CL) on the charged-lepton-flavor violation branching ratio of ℬ⁡(𝑡→𝜇⁢𝜏⁢𝑞)<8.7×10−7. An effective field theory interpretation is performed yielding 95% CL limits on Wilson coefficients, dependent on the flavor of the associated light quark and the Lorentz structure of the coupling. These range from |𝑐3⁢(2313) 𝗅𝖾𝗊𝗎|/Λ2<0.10  TeV−2 for 𝜇⁢𝜏⁢𝑢⁢𝑡 to |𝑐1⁢(2323) 𝗅𝖾𝗊𝗎|/Λ2<1.8  TeV−2 for 𝜇⁢𝜏⁢𝑐⁢𝑡. An additional interpretation is performed for scalar leptoquark production inducing charged-lepton-flavor violation, with fixed intergenerational couplings. Upper limits on leptoquark coupling strengths are set at the 95% CL, ranging from 𝜆LQ=1.3 to 𝜆LQ=3.7 for leptoquark masses between 0.5 and 2.0 TeV.