Measurements of jet observables sensitive to $b$-quark fragmentation in $t\overline{t}$ events at the LHC with the ATLAS detector

Several observables sensitive to the fragmentation of $b$ quarks into $b$ hadrons are measured using $36\text{}\text{}{\mathrm{fb}}^{-1}$ of $\sqrt{s}=13\text{}\text{}\mathrm{TeV}$ proton-proton collision data collected with the ATLAS detector at the LHC. Jets containing $b$ hadrons are obtained from a sample of dileptonic $t\overline{t}$ 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 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 $Z/{\gamma }^{*}$.