Jan 10 – 15, 2021
Weizmann Institute of Science
Asia/Jerusalem timezone
See you at IS2023 in Copenhagen in June 2023

The effect of the equation of state on $\eta/s$ of strongly interacting matter

Jan 10, 2021, 7:45 PM
1h 30m
Patio (vDLCC)



bullet talk (poster) Collective dynamics from small to large systems Poster


Jussi Auvinen (Institute of Physics Belgrade)


The properties of QCD matter produced in ultrarelativistic heavy ion collisions can be determined in a global analysis of LHC and RHIC observables. Bayesian analysis [1] has provided meaningful credibility ranges for the ratio of shear viscosity to entropy density $\eta/s$, as well as for key parameters describing the initial state, essentially confirming earlier results like those obtained using the EKRT model [2]. We report here the results of our study [3] where we investigate the temperature dependence of $\eta/s$ using a piecewise linear parametrization. We perform a global Bayesian model-to-data comparison on Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and Pb+Pb collisions at $2.76$ TeV and $5.02$ TeV, using a 2+1D hydrodynamical model, with the initial entropy distribution taken as an average of a large number of fluctuating event-by-event EKRT initial states. We provide three new parametrizations of the equation of state (EoS) based on contemporary lattice results and hadron resonance gas. We use these parametrizations, named $s83s_{18}$, $s87h_{04}$, and $s88h_{18}$, along with the earlier $s95p$ parametrization to explore the uncertainties caused by the choice of the EoS. We find $\eta/s$ most constrained and almost independent of $T$ in the temperature range $T\approx 150$--$220$ MeV, where, for all EoSs, $0.08 < \eta/s < 0.23$ when taking into account the 90% credibility intervals. In this temperature range the EoS parametrization has only a small $\sim$10% effect on the favored $\eta/s$ value, which is less than the $\sim$30% uncertainty of the analysis using a single EoS parametrization. Our parametrization of $\eta/s(T)$ leads to a slightly larger minimum value of $\eta/s(T)$ than the previously used parametrizations.

[1] J. E. Bernhard, J. S. Moreland and S. A. Bass, Nature Phys. 15, no.11, 1113-1117 (2019).
[2] H. Niemi, K. J. Eskola and R. Paatelainen, Phys. Rev. C 93, no.2, 024907 (2016).
[3] J. Auvinen, K.J. Eskola, P. Huovinen, H. Niemi, R. Paatelainen and P. Petreczky, arXiv:2006.12499 [nucl-th], to appear in Phys. Rev. C.

Primary authors

Harri Niemi (Johann Wolfgang Goethe-Universität) Jussi Auvinen (Institute of Physics Belgrade) Kari J. Eskola (University of Jyvaskyla) Pasi Huovinen (University of Wroclaw) Peter Petreczky (BNL) Risto Sakari Paatelainen (CERN)

Presentation materials