Measurements are made of differential cross-sections of highly boosted pair-produced top quarks as a function of top-quark and $t\overline{t}$ system kinematic observables using proton-proton collisions at a center-of-mass energy of $\sqrt{s}=13\mathrm{TeV}$. The data set corresponds to an integrated luminosity of $36.1{\mathrm{fb}}^{-1}$, 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 $p_{\mathrm{T}}>500\mathrm{GeV}$ and a second with $p_{\mathrm{T}}>350\mathrm{GeV}$, are used for the measurement. The top-quark candidates are separated from the multijet background using jet substructure information and association with a $b$-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 ${\chi }^2$ values. The cross-section for $t\overline{t}$ production in the fiducial phase-space region is $292\pm 7(\mathrm{stat})\pm 71(\mathrm{syst})\mathrm{fb}$, to be compared to the theoretical prediction of $384\pm 36\mathrm{fb}$.

• Received 6 January 2018

DOI:https://doi.org/10.1103/PhysRevD.98.012003

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© 2018 CERN, for the ATLAS Collaboration