Search for charged-lepton-flavor violating μτqt interactions in top-quark production and decay in pp 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 |𝑐^3⁢(2313)_{𝗅𝖾𝗊𝗎}|/Λ² <0.10  TeV⁻² for 𝜇⁢𝜏⁢𝑢⁢𝑡 to |𝑐^1⁢(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 𝜆^LQ =1.3 to 𝜆^LQ =3.7 for leptoquark masses between 0.5 and 2.0 TeV.