Measurement of the differential cross-section of highly boosted top quarks as a function of their transverse momentum using the ATLAS detector in $\sqrt{s}$ = 8 TeV proton-proton collisions

The differential cross-section for boosted top quark pair production is measured in 20.3~\ifb\ of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for $\ttbar$ events in the lepton+jets channel, where the hadronically decaying top quark has a transverse momentum above 300 GeV, and is reported as a function of the hadronically decaying top quark transverse momentum. Jet substructure techniques are employed to identify top quarks, which are reconstructed with an anti-$k_t$ jet with radius parameter $R=1.0$. The observed yield is corrected for detector effects to obtain a cross-section at particle-level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase-space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of next-to-leading-order and leading-order matrix element plus parton shower Monte Carlo generators are found to generally overestimate the measured cross-sections.