2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/176343We 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.5 pages, 4 figures. Version accepted for publication in Phys.Lett.BHigh Energy Physics - Phenomenologytext