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

Abstract

AbstractIn 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 $$D_s(T)$$ 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 $$N_f=2+1$$ N f = 2 + 1 to $$N_f=2+1+1$$ N f = 2 + 1 + 1 , where the charm quark is included. Fixing the coupling g(T) by a fit to the lQCD energy density $$\epsilon (T)$$ ϵ ( T ) , we evaluate the impact of different temperature parametrizations of charm quark mass on EoS and susceptibilities $$\chi _q(T)$$ χ q ( T ) of light, $$\chi _s(T)$$ χ s ( T ) of strange and $$\chi _c(T)$$ χ c ( T ) of charm quarks, the last favouring a charm quark mass increasing toward $$T_c$$ 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 ($$\chi _q(T)$$ χ q ( T ) , $$\chi _s(T)$$ χ s ( T ) ), which instead are underestimated in the simple QPM. Furthermore, evaluating the spatial diffusion coefficient $$2\pi T D_s(T)$$ 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 $$R_{AA}(p_T)$$ 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.