Search for Charged-Lepton Violating Μτ<i>qt</I> Interactions in Top-Quark Production and Decay in <i>pp</I> Collisions at √<i>s</I>=13 Tev With the Atlas Detector at the Lhc

Abstract

A search for charged-lepton-flavor violating mu tau qt (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 root 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 tau-lepton and at least one jet, with exactly one b-tagged jet, produced by a mu tau qt 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 -> mu tau q) < 8.7 x 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 vertical bar c(lequ)(3(2313))vertical bar/Lambda(2) < 0.10 TeV-2 for mu tau ut to vertical bar c(lequ)(1(2323))vertical bar/Lambda(2) < 1.8 TeV-2 for mu tau ct. 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 lambda(LQ) = 1.3 to lambda(LQ) = 3.7 for leptoquark masses between 0.5 and 2.0 TeV.