اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدPercolation of Color Sources and the Shear Viscosity of the QGP in Central A-A Collisions at RHIC and LHC Energies
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The Color String Percolation Model (CSPM) is used to determine the shear viscosity to entropy ratio ($eta/s$) of the Quark-Gluon Plasma (QGP) produced in Au-Au collisions at $sqrt{s_{NN}}$ = 200 GeV at RHIC and Pb-Pb at $sqrt{s_{NN}}$ = 2.76 TeV at LHC. The relativistic kinetic theory relation for $eta/s$ is evaluated using CSPM values for the temperature and the mean free path of the QGP constituents. The experimental charged hadron transverse momentum spectrum is used to determine the percolation density parameter $xi$ in Au-Au collisions (STAR). For Pb-Pb at $sqrt{s_{NN}}$ = 2.76 TeV $xi$ values are obtained from the extrapolation at RHIC energy. The value of $eta/s$ is 0.204$pm$0.020 and 0.262$pm$0.026 at the CSPM initial temperatures of 193.6$pm$3 MeV (RHIC) and 262.2 $pm$13 MeV (LHC) respectively. These values are 2.5 and 3.3 times the AdS/CFT conjectured lower bound $1/4pi$. We compare the CSPM $eta/s$ analytic expression with weak coupling (wQGP) and strong coupling (sQGP) calculations. This indicates that the QGP is a strongly coupled fluid in the phase transition region.
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The initial temperature $T_{i}$, energy density $varepsilon_{i}$, and formation time $tau_{i}$ of the initial state of the QGP formed in the heavy ion collisions at RHIC and LHC energies are determined using the data driven Color String Percolation M
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The Color String Percolation Model (CSPM) is used to determine the equation of state (EOS) of the QGP produced in central Au-Au collisions at $sqrt{s_{NN}}$ = 200 A GeV using STAR data at RHIC. When the initial density of interacting colored strings
exceeds the 2D percolation threshold a cluster is formed, which defines the onset of color deconfinement. These interactions also produce fluctuations in the string tension which transforms the Schwinger particle (gluon) production mechanism into a maximum entropy thermal distribution. The single string tension is determined by identifying the known value of the universal hadron limiting temperature $T_{c}$ = 167.7 $pm$ 2.6 MeV with the CSPM percolation temperature at the critical threshold $xi_{c}$ =1.2. At mid-rapidity the initial Bjorken energy density and the initial temperature determine the number of degrees of freedom consistent with the formation of a $sim$ 2+1 flavor QGP. An analytic expression for the equation of state, the sound velocity $C_{s}^{2}(xi)$ is obtained in CSPM. The CSPM $C_{s}^{2}(xi)$ and the bulk thermodynamic values $varepsilon /T^{4}$ and $s /T^{3}$ are in excellent agreement in the phase transition region with recent lattice QCD simulations (LQCD) by the HotQCD Collaboration.
The progress over the 30 years since the first high-energy heavy-ion collisions at the BNL-AGS and CERN-SPS has been truly remarkable. Rigorous experimental and theoretical studies have revealed a new state of the matter in heavy-ion collisions, the
quark-gluon plasma (QGP). Many signatures supporting the formation of the QGP have been reported. Among them are jet quenching, the non-viscous flow, direct photons, and Debye screening effects. In this article, selected signatures of the QGP observed at RHIC and the LHC are reviewed.
Possible phase transition of strongly interacting matter from hadron to a quark-gluon plasma state have in the past received c onsiderable interest. It has been suggested that this problem might be treated by percolation theory. The clustering of col
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