  The normalized differential cross section for top quark pair (tt-bar)
production is measured in pp collisions at a centre-of-mass energy of 8 TeV at
the CERN LHC using the CMS detector in data corresponding to an integrated
luminosity of 19.7 inverse femtobarns. The measurements are performed in the
lepton + jets (e/mu + jets) and in the dilepton (e+e-, mu+mu-, and e+-mu-+)
decay channels. The tt-bar cross section is measured as a function of the
kinematic properties of the charged leptons, the jets associated to b quarks,
the top quarks, and the tt-bar system. The data are compared with several
predictions from perturbative quantum chromodynamics up to approximate
next-to-next-to-leading-order precision. No significant deviations are observed
relative to the standard model predictions.
