Quasi particle model vs lattice QCD thermodynamics: extension to Nf=2+1+1 flavors and momentum dependent quark masses

In the last decade a quasi-particle model (QPM) has supplied the basis for the study of heavy quark (HQ) production in ultra-relativistic collisions, allowing for a phenomenological estimate of the HQ diffusion coefficient Dₛ(T) D s ( T ) . Using the new lattice QCD results for the equation of state (EoS) with 2+1+1 dynamical flavors, we extend the QPM from Nf=2+1 N f = 2 + 1 to Nf=2+1+1 N f = 2 + 1 + 1 , where the charm quark is included. Fixing the coupling g ( T ) by a fit to the lQCD energy density ε (T) ϵ ( T ) , we evaluate the impact of different temperature parametrizations of charm quark mass on EoS and susceptibilities χ q(T) χ q ( T ) of light, χ ₛ(T) χ s ( T ) of strange and χ c(T) χ c ( T ) of charm quarks, the last favouring a charm quark mass increasing toward Tc T c . We also explore the extension of the QPM to a more realistic approach called QPM ₚ p , where quark and gluon masses explicitly depend on their momentum converging to the current quark mass at high momenta, as expected from asymptotic free dynamics. The QPM ₚ p allows for a simultaneous quantitative description not only of the EoS but also of the quark susceptibilities ( χ q(T) χ q ( T ) , χ ₛ(T) χ s ( T ) ), which instead are underestimated in the simple QPM. Furthermore, evaluating the spatial diffusion coefficient 2π T Dₛ(T) 2 π T D s ( T ) in the QPM ₚ p , we find it is also closer than QPM to the recent lQCD data performed including dynamical fermions. Finally, in a 1+1D expanding system, we evaluate the RAA(pT) R AA ( p T ) in the QPM and QPM ₚ p , finding a significant reduction at low momenta for QPM ₚ p which could lead in a realistic scenario to a better agreement to experimental data.