  Measurements of normalized differential cross-sections of top quark pair
($t\bar t$) production are presented as a function of the mass, the transverse
momentum and the rapidity of the $t\bar t$ system in proton-proton collisions
at center-of-mass energies of $\sqrt{s}$ = 7 TeV and 8 TeV. The dataset
corresponds to an integrated luminosity of 4.6 fb$^{-1}$ at 7 TeV and 20.2
fb$^{-1}$ at 8 TeV, recorded with the ATLAS detector at the Large Hadron
Collider. Events with top quark pair signatures are selected in the dilepton
final state, requiring exactly two charged leptons and at least two jets with
at least one of the jets identified as likely to contain a $b$-hadron. The
measured distributions are corrected for detector effects and selection
efficiency to cross-sections at the parton level. The differential
cross-sections are compared with different Monte Carlo generators and
theoretical calculations of $t\bar t$ production. The results are consistent
with the majority of predictions in a wide kinematic range.
