  We study the correlations of heavy quarks produced in relativistic heavy ion
collisions and find them to be quite sensitive to the effects of the medium and
the production mechanisms. In order to put this on a quantitative footing, as a
first step, we analyze the azimuthal, transverse momentum, and rapidity
correlations of heavy quark-anti quark ($Q\overline{Q}$) pairs in $pp$
collisions at $\cal{O}$($\alpha_{s}^{3}$). This sets the stage for the
identification and study of medium modification of similar correlations in
relativistic collision of heavy nuclei at the Large Hadron Collider. Next we
study the additional production of charm quarks in heavy ion collisions due to
multiple scatterings, {\it viz.}, jet-jet collisions, jet-thermal collisions,
and thermal interactions. We find that these give rise to azimuthal
correlations which are quite different from those arising from prompt initial
production at leading order and at next to leading order.
