Abstract
AbstractWe 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 μB 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 Tc from lattice quantum chromodynamics (QCD). We calculate the collisional widths for the partonic degrees of freedom at finite T and μB in the time‐like sector and conclude that the quasiparticle limit holds sufficiently well. Furthermore, the ratio of shear viscosity η over entropy density s, that is, η/s, is evaluated using the collisional widths and compared to lattice QCD(lQCD) calculations for μB = 0 as well. We find that the ratio η/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 η/s with the baryon chemical μB as a function of the scaled temperature T/Tc(μB). This also holds for a variety of hadronic observables from central A + A collisions in the energy range 5 GeV 200 GeV when implementing the differential cross sections into the PHSD approach. Accordingly, it will be difficult to extract finite μB signals from the partonic dynamics based on “bulk” observables.
Highlights
The phase transition from partonic degrees of freedom to interacting hadrons is a central topic of modern high-energy physics
The following elastic and inelastic interactions are included in parton–hadron–string dynamics (PHSD) qq ↔ qq, q q ↔ q q, gg ↔ gg, gg ↔ g, qq ↔ g, qg ↔ qg, gq ↔ gq exploiting “detailed-balance” with cross sections calculated from the leading Feynman diagrams using the effective propagators and couplings g2(T/Tc) from the dynamical quasiparticle model (DQPM) (Moreau et al 2019)
We mention that, when implementing the differential cross sections and parton masses into the PHSD5.0 approach, one has to specify the” Lagrange parameters” T and μB in each computational cell in space–time. This has been conducted by using the lattice equation of state, which is practically identical to the lattice quantum chromodynamics (QCD) equation of state, and a diagonalization of the energy–momentum tensor from PHSD as described in Moreau et al (2019)
Summary
The phase transition from partonic degrees of freedom (quarks and gluons) to interacting hadrons is a central topic of modern high-energy physics. As relativistic heavy-ion collisions start with impinging nuclei in their ground states, a proper nonequilibrium description of the entire dynamics through possibly different phases up to the final asymptotic hadronic states—eventually showing some degree of equilibration—is mandatory. To this aim, the parton–hadron–string dynamics (PHSD) transport approach (Bratkovskaya et al 2011; Linnyk et al 2013) has been formulated about a decade ago and was found to well describe observables from p + A and A + A collisions from SPS to LHC energies, including electromagnetic probes such as photons and dileptons (Linnyk et al 2016). In order to explore the partonic systems at higher μB, the PHSD approach is extended to incorporate partonic quasiparticles and their differential cross sections that depend on T and μB explicitly
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
