D-Dbar Correlations as a sensitive probe for thermalization in   high-energy nuclear collisions
  We propose to measure azimuthal correlations of heavy-flavor hadrons to address the status of thermalization at the partonic stage of light quarks and gluons in high-energy nuclear collisions. In particular, we show that hadronic interactions at the late stage cannot significantly disturb the initial back-to-back azimuthal correlations of DDbar pairs. Thus, a decrease or the complete absence of these initial correlations does indicate frequent interactions of heavy-flavor quarks and also light partons in the partonic stage, which are essential for the early thermalization of light partons. 
X. Zhu, M. Bleicher, S.L. Huang, K. Schweda, H. Stoecker, N. Xu, P.   Zhuang