  The differential cross-section for pair production of top quarks with high
transverse momentum is measured in 20.3 fb$^{-1}$ of proton-proton collisions
at a center-of-mass energy of 8 TeV. The measurement is performed for
$t\bar{t}$ events in the lepton+jets channel. The cross-section is reported as
a function of the hadronically decaying top quark transverse momentum for
values above 300 GeV. The hadronically decaying top quark is reconstructed as
an anti-$k_t$ jet with radius parameter $R=1.0$ and identified with jet
substructure techniques. 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 a majority of next-to-leading-order and leading-order
matrix-element Monte Carlo generators are found to agree with the measured
cross-sections.
