Abstract
Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and π‘β’Β―π‘ system kinematic observables using proton-proton collisions at a center-of-mass energy of βπ =13ββTeV. The data set corresponds to an integrated luminosity of 36.1ββfbβ1, recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Events with two large-radius jets in the final state, one with transverse momentum πT >500ββGeV and a second with πT >350ββGeV, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a π-tagged jet. The measured spectra are corrected for detector effects to a particle-level fiducial phase space and a parton-level limited phase space, and are compared to several Monte Carlo simulations by means of calculated π2 values. The cross-section for π‘β’Β―π‘ production in the fiducial phase-space region is 292Β±7β’(stat)Β±71β’(syst)ββfb, to be compared to the theoretical prediction of 384 Β±36ββfb.