12-18 August 2012
US/Eastern timezone

If you have any questions about the details of the program please contact Bolek Wyslouch

Relation Between the Trace Anomaly and Shear Viscosity in Clustering of Color Sources and the Equation of State of the QGP

16 Aug 2012, 16:00
Regency 1/3 and Ambassador

Regency 1/3 and Ambassador

Poster QCD at finite temperature and density Poster Session Reception


Prof. Rolf Scharenberg (Purdue University)


The major challenge in heavy ion physics is to extract the equation of state and the shear viscosity to entropy ratio $\eta/s$ from the data. In the clustering of color sources (CSPM) the charged particle transverse momentum spectrum is used to measure the percolation density parameter $\xi$, which determines the initial temperature T, energy density $\epsilon$, and the $\eta/s$ ratio versus T in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV . For 0.9 $T_{c} < T < $1.2 $T_{c}$ ($T_{c}$ = 167.7 MeV), the sound velocity $C_{s}^{2}$ from the mass less non interacting constituent version of CSPM agrees with Lattice QCD (LQCD)$C_{s}^{2}$ values . For T$ >$ 1.2$T_{c}$ there is a significant difference with the LQCD values\cite{eos}. The measured CSPM value for $\eta/s$ = 0.20, at 1.15$T_{c}$ is consistent with a strongly coupled QGP and increases with T. The Trace Anomaly $\triangle $ is defined as $(\epsilon-3p)/T^{4}$. Above $T_{c}$, the LQCD $\triangle $ and the reciprocal of $\eta/s$ fall off with 1/T. At $T_{c}$ , $s/\eta$ has a magnitude of $\sim$5.5 , non interacting - CSPM has a $\triangle\sim$ 5.5 and LQCD $\triangle \sim $5.5. The change in $\triangle$ and $s/\eta$ with 1/T describes the transition from a strongly to weakly coupled QGP. Above $T_{c}$, $s/\eta$ and the LQCD $\triangle$ may have the same underlying structure. The $C_{s}^{2}$ values for the QGP obtained using the $s/\eta \sim 5.5$ version of CSPM above $T_{c}$ are in excellent agreement with LQCD \cite{wupp, hotqcd}. The CSPM predictions for Pb-Pb and p-p collisions at LHC energies will be presented.

Primary author

Prof. Rolf Scharenberg (Purdue University)


Prof. Andrew Hirsch (Purdue University) Brijesh Kumar Srivastava (Purdue University (US))

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