We study the effect of thermal charm production on charmonium regeneration in high energy nuclear collisions. By solving the kinetic equations for charm quark and charmonium distributions in Pb+Pb collisions, we calculate the global and differential nuclear modification factors R AA (N part ) and R AA (p t ) for J/ψs. Due to the thermal charm production in hot medium, the charmonium production source changes from the initially created charm quarks at SPS, RHIC and LHC to the thermally produced charm quarks at Future Circular Collider (FCC), and the J/ψ suppression (R AA < 1) observed so far will be replaced by a strong enhancement (R AA > 1) at FCC at low transverse momentum. 12.38.Mh, 24.85.+p Statistical Quantum Chromodynamics (QCD) predicts that, a strongly interacting matter will undergo a deconfinement phase transition from hadron matter to quark matter at finite temperature and density. It is expected that, this new state of matter, the so-called quark gluon plasma (QGP), can be created by liberating quarks and gluons from hadrons through high energy nuclear collisions. Since the QGP can only exist in the initial period and cannot be directly observed in the final state of the collisions, one needs sensitive probes to demonstrate the formation of this new state. J/ψ suppression has long been considered as such a probe since the original work of Matsui and Satz [1], and many progresses have been achieved both experimentally and theoretically, see for instance the recent review paper [2,3]. While the charmonium production mechanism changes from initial production at SPS energy [4-6] to initial production plus regeneration at RHIC and LHC energies [7][8][9][10][11][12][13][14], the charm quarks are all from the initial production.Recently, the Future Circular Collider (FCC) at CERN is proposed to push the energy frontier beyond LHC, which includes the plan of Pb+Pb collision at √ s NN = 39 TeV [15].What would we expect about the charmonium production at this new energy regime? Since a much more hot medium will emerge at FCC, gluons and light quarks inside the medium would be more energetic and denser. Therefore, the thermal production of charm quarks via gluon fusion and quark and anti-quark annihilation may have a sizeable effect on charmonium regeneration. For the in-medium charm quark production, there are already many studies, by considering leading order [16][17][18] and including next to leading order [19] QCD processes. Taking into account the quadratic dependence of the charmonium regeneration on charm quark density, we expect that, the extra increase of charm quark pairs via the thermal production in QGP will obviously enhance the charmonium yield at FCC. Since the very hot medium can eat up almost all the initially produced charmonia, the regeneration becomes the only source of the finally observed soft charmonia. This makes J/ψ more effective to probe the medium properties. In this paper, we focus on the effect of thermal charm production on charmonium production in heavy ion collisions at LHC a...
According to the Kubo formulas we employ the (3+1)-d parton cascade, Boltzmann approach of multiparton scatterings (BAMPS), to calculate the anisotropic transport coefficients (shear viscosity and electric conductivity) for an ultrarelativistic Boltzmann gas in the presence of a magnetic field. The results are compared with those recently obtained by using the Grad's approximation. We find good agreements between both results, which confirms the general use of the derived Kubo formulas for calculating the anisotropic transport coefficients of quark-gluon plasma in a magnetic field.
We calculate the shear viscosity of ultrarelativistic Boson systems in the presence of Bose-Einstein condensate (BEC). Two different methods are used. One is the Grad's method of moments and another is the Green-Kubo relation within a kinetic transport approach. In this work we consider a Boson system with isotropic elastic collisions and a gluon system with elastic scatterings described by perturbation QCD (pQCD). The results show that the presence of BEC lowers the shear viscosity. This effect becomes stronger for the increasing proportion of the BEC in the Boson system and is insensitive to the detail of interactions.
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