  We study the nuclear modification of angular and momentum correlations
between heavy quark pairs in ultrarelativistic heavy-ion collisions. The
evolution of heavy quarks inside the thermalized medium is described via a
modified Langevin approach that incorporates both elastic and inelastic
interactions with the medium constituents. The spacetime evolution of the
fireball is obtained from a (2+1)-dimensional viscous hydrodynamics simulation.
The hadronization of heavy quarks is performed utilizing a hybrid model of
fragmentation and coalescence. Our results show that the nuclear modification
of the transverse momentum imbalance of D\bar{D} pairs reflects the total
energy loss experienced by the heavy quarks and may help us probe specific
regions of the medium. The angular correlation of heavy flavor pairs,
especially in the low to intermediate transverse momentum regime, is sensitive
to the detailed energy loss mechanism of heavy quarks inside the QGP.
