Measurements of jet observables sensitive to b-quark fragmentation in tt¯ 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 t ¯ t events, and the associated set of charged-particle tracks is separated into those from the primary p p 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 several modern Monte Carlo parton-shower generators and generator tunes, and a wide range of agreement with the data is observed, with p values varying from 5 × 10 − 4 to 0.98. These measurements complement similar measurements from e + e − collider experiments in which the b quarks originate from a color singlet Z / γ ∗ . publishedVersion