Measurement of the c-jet mistagging efficiency in t(t)over-bar events using pp collision data at root s=13 TeV collected with the ATLAS detector
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A technique is presented to measure the effi-ciency with whichc-jets are mistagged asb-jets (mistaggingefficiency) usingt ̄tevents, where one of theWbosons decaysinto an electron or muon and a neutrino and the other decaysinto a quark–antiquark pair. The measurement utilises therelatively large and knownW→csbranching ratio, whichallows a measurement to be made in an inclusivec-jet sample.The data sample used was collected by the ATLAS detectorat√s=13 TeV and corresponds to an integrated luminos-ity of 139 fb−1. Events are reconstructed using a kinematiclikelihood technique which selects the mapping between jetsandt ̄tdecay products that yields the highest likelihood value.The distribution of theb-tagging discriminant for jets fromthe hadronicWdecays in data is compared with that in sim-ulation to extract the mistagging efficiency as a function ofjet transverse momentum. The total uncertainties are in therange 3–17%. The measurements generally agree with thosein simulation but there are some differences in the region cor-responding to the most stringentb-jet tagging requirement.