Modification of the spectra of correlated charm-anticharm quark pairs in the quark-gluon plasma

Heavy quarks play an important role in probing the properties of strongly interacting quark-gluon plasma（QGP） created in ultra-relativistic heavy-ion collisions.We study the interactions of single heavy（charm） quarks and correlated charm and anticharm（cc） quark pairs with the medium constituents of QGP by performing fireball+Langevin simulations of the pertinent Brownian motion with elastic collisions.Besides studying the traditional observables,the nuclear modification factor and the elliptic flow of single heavy quarks in QGP for different thermal relaxation rates,we also study the broadening of the azimuthal correlations of charm and anticharm quark pairs in the QGP medium for different relaxation rates and transverse momenta classes.We quantified the smearing of cc pair azimuthal correlations with an increasing thermal relaxation rate:while the（nearly） back-to-back correlations among cc pairs are almost completely washed out at low transverse momentum（pT）,these correlations at high pT largely survive the pair diffusion.This provides a novel observable for diagnosing the properties of QGP.