Abstract
A search for charged-lepton-flavour violating μτqt (q=u,c) interactions is presented, considering both top-quark production and decay. The data analysed correspond to 140 fb−1 of proton-proton collisions at a centre-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 μτqt interaction. Agreement with the Standard Model expectation within 1.6σ is observed, and limits are set at the 95% CL on the charged-lepton-flavour violation branching ratio of B(t→μτq)<8.7×10−7. An Effective Field Theory interpretation is performed yielding 95% CL limits on Wilson coefficients, dependent on the flavour of the associated light quark and the Lorentz structure of the coupling. These range from |c3(2313)lequ|/Λ2<0.10 TeV−2 for μτut to |c1(2323)lequ|/Λ2<1.8 TeV−2 for μτct. An additional interpretation is performed for scalar leptoquark production inducing charged lepton flavour violation, with fixed inter-generational 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.