  Measurements of normalized differential cross-sections of top-quark pair
production are presented as a function of the top-quark, $t\bar{t}$ system and
event-level kinematic observables in proton-proton collisions at a
centre-of-mass energy of $\sqrt{s}=8$ TeV}. The observables have been chosen to
emphasize the $t\bar{t}$ production process and to be sensitive to effects of
initial- and final-state radiation, to the different parton distribution
functions, and to non-resonant processes and higher-order corrections. The
dataset corresponds to an integrated luminosity of 20.3 fb$^{-1}$, recorded in
2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are
selected in the lepton+jets channel, requiring exactly one charged lepton and
at least four jets with at least two of the jets tagged as originating from a
$b$-quark. The measured spectra are corrected for detector effects and are
compared to several Monte Carlo simulations. The results are in fair agreement
with the predictions over a wide kinematic range. Nevertheless, most generators
predict a harder top-quark transverse momentum distribution at high values than
what is observed in the data. Predictions beyond NLO accuracy improve the
agreement with data at high top-quark transverse momenta. Using the current
settings and parton distribution functions, the rapidity distributions are not
well modelled by any generator under consideration. However, the level of
agreement is improved when more recent sets of parton distribution functions
are used.
