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

Abstract 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 (T) ϵ (T), we evaluate the impact of different temperature parametrizations of charm quark mass on EoS and susceptibilities q (T) χ q (T) of light, ₛ (T) χ s (T) of strange and 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 (q (T) χ q (T), ₛ (T) χ s (T) ), which instead are underestimated in the simple QPM. Furthermore, evaluating the spatial diffusion coefficient 2 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 R₀₀ (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.