Variation of jet quenching from RHIC to LHC and thermal suppression of the QCD coupling constant

We perform a joint jet tomographic analysis of the data on the nuclear modification factor R _AA from PHENIX at RHIC and ALICE at LHC. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant. Our results show that the observed slow variation of R _AA from RHIC to LHC indicates that the QCD coupling constant is suppressed in the quark-gluon plasma produced at LHC.