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Description
We derive a diffusion coefficient of quarks propagating through a strongly coupled plasma from the AdS/CFT correspondence. This diffusion coefficient interpolates between light and heavy flavour. In contradistinction to past results, this diffusion coefficient does not increase with quark velocity. Taking our diffusion coefficient derivation as fundamental, we use the fluctuation-dissipation theorem to predict a strong-coupling heavy quark drag that is slightly different from the original calculations of Gubser and Herzog et al.
From this result, we compute the suppression, angular, and rapidity distribution of single open heavy flavour and the momentum, angular, and rapidity correlations for pairs of open heavy flavour at RHIC and LHC from an AdS/CFT-based energy loss model. We quantitatively compare these strongly-coupled QGP predictions to the weakly-coupled QGP predictions of Nahrgang et al., PRC90 (2014) [arXiv:1305.3823].
We find that the strongly coupled correlations of high transverse momentum pairs (>4GeV) are broadened less efficiently than the corresponding weak coupling based correlations, while low transverse momentum pairs (1−4GeV) are broadened with similar efficiency, but with an order of magnitude more particles ending up in this momentum class. The strong coupling momentum correlations we compute account for initial correlations and reveal that the particle pairs suppressed from initially high momenta to the low momentum domain do not suffice to explain the stark difference to the weak coupling results in momentum correlations for 1−4GeV. From this, we conclude that heavy quark pairs are more likely to stay correlated in momentum when propagating through a strongly coupled plasma than a weakly coupled one.
We also compare our predictions with experimental data from ALICE and CMS. We find good agreement with both B and D suppression data, unlike earlier AdS/CFT based calculations.
Summary
We present a new derivation of the heavy quark diffusion coefficient in a strongly-coupled plasma using the AdS/CFT correspondence. Our main result is that, unlike some previous calculations, our diffusion coefficient does not increase with heavy quark velocity: we find that the effect of momentum fluctuations smoothly interpolates between light and heavy flavors.
We use this diffusion coefficient to compare the azimuthal and momentum correlations of bottom pairs in Pb+Pb collisions of our model with pQCD calculations. Our comparison demonstrates that low momentum correlations (1–4GeV) serve as a potential distinguishing observable between weakly and strongly coupled plasmas.