Probing the transport properties of quark-gluon plasma via heavy-flavor Boltzmann and Langevin dynamics

Abstract

The heavy quark propagation behavior inside the quark-gluon plasma (QGP), is usually described in terms of the Boltzmann dynamics, which can be reduced to the Langevin approach by assuming a small momentum transfer for the scattering processes between heavy quarks and the QGP constituents. In this work, the temperature and energy dependence of the transport coefficients are calculated in the framework of both Boltzmann and Langevin dynamics, by considering only the elastic scattering processes to have a better comparison and understanding of these two models. The extracted transport coefficients are found to be larger in the Boltzmann approach as compared with the Langevin, in particular in the high-temperature and high-energy region. Within each of the two theoretical frameworks, we simulate the charm quark production and the subsequent evolution processes in relativistic heavy-ion collisions. We find that the energy loss due to elastic scattering is larger from the Boltzmann dynamics, resulting in a smaller RAA at high pT (pT ≳ 10 GeV), for both the charm quark and heavy-flavor mesons. The Boltzmann model produces systematically larger v2, in particular at moderate pT, meanwhile, it shows a stronger broadening behavior for the relative azimuthal angle between initially back-to-back generated cc¯ pairs in the similar region. They are mainly induced by the stronger interactions between heavy quarks and the QGP partons in Boltzmann, which are able to transfer more v2 from the medium to the heavy quarks, as well as to pull more cc¯ pairs from high momentum to low momentum. By comparing the model calculations with available experimental measurements for D mesons, a visible deviation can be observed for both the Boltzmann and Langevin approaches. The missing inelastic contributions allow reducing the discrepancy with data, and additionally, the relevant Langevin approach is more favored by the RAA data while the Boltzmann approach is more favored favor by the v2 data. A simultaneous description of both observables appears challenging for both models.