We extend the parton-hadron string dynamics (PHSD) transport approach in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections as a function of temperature T and baryon chemical potential mu(B) on the basis of the effective propagators and couplings from the dynamical quasiparticle model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature T-c from lattice QCD. We calculate the collisional widths for the partonic degrees of freedom at finite T and mu(B) in the timelike sector and conclude that the quasiparticle limit holds sufficiently well. Furthermore, the ratio of shear viscosity. over entropy density s, i.e., eta/s, is evaluated using the collisional widths and compared to lattice QCD calculations for mu(B) = 0 as well. We find that the novel ratio eta/s does not differ very much from that calculated within the original DQPM on the basis of the Kubo formalism. Furthermore, there is only a very modest change of eta/s with the baryon chemical mu(B) as a function of the scaled temperature T/T-c (mu(B)). This also holds for a variety of hadronic observables from central A + A collisions in the energy range 5 GeV <= root s(NN) <= 200 GeV when implementing the differential cross sections into the PHSD approach. We only observe small differences in the antibaryon sector ((p) over bar, (Lambda) over bar + (Sigma) over bar (0)) at root s(NN) = 17.3 GeV and 200 GeV with practically no sensitivity of rapidity and p(T) distributions to the mu(B) dependence of the partonic cross sections. Small variations in the strangeness sector are obtained in all collisional systems studied (Lambda + Lambda and C + Au); however, it will be very hard to extract a robust signal experimentally. Since we find only small traces of a mu B dependence in heavy-ion observables-although the effective partonic masses and widths as well as their partonic cross sections clearly depend on mu(B)-this implies that one needs a sizable partonic density and large space-time QGP volume to explore the dynamics in the partonic phase. These conditions are only fulfilled at high bombarding energies where mu(B) is, however, rather low. On the other hand, when decreasing the bombarding energy and thus increasing mu(B), the hadronic phase becomes dominant and accordingly it will be difficult to extract signals from the partonic dynamics based on "bulk" observables.
Exploring the partonic phase at finite chemical potential within an extended off-shell transport approach
Lucia Oliva;
2019-01-01
Abstract
We extend the parton-hadron string dynamics (PHSD) transport approach in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections as a function of temperature T and baryon chemical potential mu(B) on the basis of the effective propagators and couplings from the dynamical quasiparticle model (DQPM) that is matched to reproduce the equation of state of the partonic system above the deconfinement temperature T-c from lattice QCD. We calculate the collisional widths for the partonic degrees of freedom at finite T and mu(B) in the timelike sector and conclude that the quasiparticle limit holds sufficiently well. Furthermore, the ratio of shear viscosity. over entropy density s, i.e., eta/s, is evaluated using the collisional widths and compared to lattice QCD calculations for mu(B) = 0 as well. We find that the novel ratio eta/s does not differ very much from that calculated within the original DQPM on the basis of the Kubo formalism. Furthermore, there is only a very modest change of eta/s with the baryon chemical mu(B) as a function of the scaled temperature T/T-c (mu(B)). This also holds for a variety of hadronic observables from central A + A collisions in the energy range 5 GeV <= root s(NN) <= 200 GeV when implementing the differential cross sections into the PHSD approach. We only observe small differences in the antibaryon sector ((p) over bar, (Lambda) over bar + (Sigma) over bar (0)) at root s(NN) = 17.3 GeV and 200 GeV with practically no sensitivity of rapidity and p(T) distributions to the mu(B) dependence of the partonic cross sections. Small variations in the strangeness sector are obtained in all collisional systems studied (Lambda + Lambda and C + Au); however, it will be very hard to extract a robust signal experimentally. Since we find only small traces of a mu B dependence in heavy-ion observables-although the effective partonic masses and widths as well as their partonic cross sections clearly depend on mu(B)-this implies that one needs a sizable partonic density and large space-time QGP volume to explore the dynamics in the partonic phase. These conditions are only fulfilled at high bombarding energies where mu(B) is, however, rather low. On the other hand, when decreasing the bombarding energy and thus increasing mu(B), the hadronic phase becomes dominant and accordingly it will be difficult to extract signals from the partonic dynamics based on "bulk" observables.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
