Parton-medium cross section and average QGP viscosity in lead-lead collisions at LHC

Abstract

The recent experimental CMS and E-by-E ATLAS data on the elliptic anisotropy of particles in \PbPb collisions are used to extract parton medium cross-section and the quark-gluon plasma viscosity-to-entropy ratio within the incomplete equilibration medium model. Our method assumes extrapolation of the measured pseudorapidity spectrum of charged particles to low-$p_T$ range. Then the rapidity distribution of both charged and neutral hadrons is restored. The extracted value of the parton-medium cross section is found to be $\text{ds}\sigma =(3.1\pm 0.2)\mathrm{mb}$. It yields $\eta /s=0.17\pm 0.02$ for the ratio of shear viscosity to entropy density in QGP phase. The last result is in a good agreement with the estimates obtained by calculations within the viscous hydrodynamics.

Comments: 12 pages, 1 figure. arXiv admin note: text overlap with arXiv:1204.1409 by other authors