Measurements of jet observables sensitive to b-quark fragmentation in tt̅ events at the LHC with the ATLAS detector

Several observables sensitive to the fragmentation of b-quarks into b-hadrons are measured using 36 fb⁻¹ of √s = 13 TeV proton-proton collision data collected with the ATLAS detector at the LHC. Jets containing b-hadrons are obtained from a sample of dileptonic tt̅ events, and the associated set of charged-particle tracks is separated into those from the primary pp interaction vertex and those from the displaced b-decay secondary vertex. This division is used to construct observables that characterize the longitudinal and transverse momentum distributions of the b-hadron within the jet. The measurements have been corrected for detector effects and provide a test of heavy-quark-fragmentation modeling at the LHC in a system where the top-quark decay products are color-connected to the proton beam remnants. The unfolded distributions are compared with the predictions of modern Monte Carlo parton-shower generators, and these predictions are found to be largely in agreement with the observed data. These measurements complement similar measurements from e⁺e⁻ collider experiments in which the b-quarks originate from a color-singlet Z/γ^∗.