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1
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Refractive index of light and the quark-gluon plasma

100%
Liu J., Luo M.-J., Xu H.-J.
Open Physics
|
2012
|
vol. 10
|
issue 6
1369-1371
EN
The refractive index (RI) of light propagating in a medium of quark-gluon plasma (QGP) is studied. The weakly coupled QGP is studied in the framework of hard-thermal-loop (HTL) perturbation theory, and the strongly coupled one is treated based on the holographic approach. In more realistic setups, the feasibility of observing the optical phenomenon related to the RI of QGP is also discussed.
2
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Baryon number cumulants and proton number cumulants in relativistic heavy ion collisions

80%
Asakawa M.
Open Physics
|
2012
|
vol. 10
|
issue 6
1314-1317
EN
Baryon number cumulants are invaluable tools to diagnose the primordial stage of heavy ion collisions. In experiments, however, proton number cumulants have been measured as substitutes. In fact, proton number fluctuations are further modified in the hadron phase and different from those of baryon number. We give formulas that express the baryon number cumulants solely in terms of proton number fluctuations, which are experimentally observable.
3
Content available remote

What favors and disfavors the critical point of QCD?

80%
Fukushima K.
Open Physics
|
2012
|
vol. 10
|
issue 6
1318-1321
EN
Results from chiral effective models suggest the existence of the so-called QCD critical point. These model predictions are highly dependent on the model setup and there is no universal argument for its existence and location. I discuss why a first-order phase transition is generally favored in models at low temperature T and high chemical potential µ, which will explain why the model results are unreliable about the critical point. I propose a useful way to reinterpret the model results as a liquid-gas-type phase transition like that of nuclear matter. This picture provides us with a fairly model-independent description of the QCD critical point not relying on detailed phase structures.
4
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Determination of freeze-out conditions from lattice QCD calculations

80%
Karsch F.
Open Physics
|
2012
|
vol. 10
|
issue 6
1234-1237
EN
Freeze-out conditions in Heavy Ion Collisions are generally determined by comparing experimental results for ratios of particle yields with theoretical predictions based on applications of the Hadron Resonance Gas model. We discuss here how this model dependent determination of freeze-out parameters may eventually be replaced by theoretical predictions based on equilibrium QCD thermodynamics.
5
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Equation of state and initial temperature of quark gluon plasma at RHIC

80%
Csanád M., Májer I.
Open Physics
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2012
|
vol. 10
|
issue 4
850-857
EN
In gold-gold collisions of the Relativistic Heavy Ion Collider a perfect fluid of strongly interacting quark gluon plasma (sQGP) is created. The time evolution of this fluid can be described by hydrodynamical models. After an expansion, hadrons are created during the freeze-out period. Their distribution reveals information about the final state. To investigate the time evolution one needs to analyze penetrating probes: e.g. direct photon observations. In this paper we analyze a 1+3 dimensional solution of relativistic hydrodynamics. We calculate momentum distribution, azimuthal asymmetry and momentum correlations of direct photons. Based on earlier fits to hadronic spectra, we compare photon calculations to measurements to determine the equations of state and the initial temperature of sQGP. We find that the initial temperature in the center of the fireball is 507±12 MeV, while for the sound speed we get c s=0.36±0.02. We also estimate a systematic error of these results. We find that the measured azimuthal asymmetry is also compatible with this model. We also predict a photon source that is significantly larger in the out direction than in the side direction.
6
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Dilepton creation based on an analytic hydrodynamic solution

80%
Csanád M., Krizsán L.
Open Physics
|
2014
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vol. 12
|
issue 2
132-140
EN
High-energy collisions of various nuclei, so called “Little Bangs” are observed in various experiments of heavy ion colliders. The time evolution of the strongly interacting quark-gluon plasma created in heavy ion collisions can be described by hydrodynamical models. After expansion and cooling, the hadrons are created in a freeze-out. Their distribution describes the final state of this medium. To investigate the time evolution one needs to analyze penetrating probes, such as direct photon or dilepton observables, as these particles are created throughout the evolution of the medium. In this paper we analyze an 1+3 dimensional analytic solution of relativistic hydrodynamics, and we calculate dilepton transverse momentum and invariant mass distributions. We investigate the dependence of dilepton production on time evolution parameters, such as emission duration and equation of state. Using parameters from earlier fits of this model to photon and hadron spectra, we compare our calculations to measurements as well. The most important feature of this work is that dilepton observables are calculated from an exact, analytic, 1+3D solution of relativistic hydrodynamics that is also compatible with hadronic and direct photon observables.
7
Content available remote

Hard-thermal-loop QCD trace anomaly

70%
Su N.
Open Physics
|
2012
|
vol. 10
|
issue 6
1379-1381
EN
In this proceedings I summarize results of QCD trace anomaly from recent three-loop hard-thermal-loop perturbation theory (HTLpt) calculations. I focus on the trace anomaly scaled by T 2 for pure-glue and N f = 3 QCD. The comparison to available lattice data suggests that for pure-glue QCD agreement between HTLpt results and lattice data for the trace anomaly begins at temperatures above 8 T c while when including quarks (N f = 3) agreement begins already at temperatures above 2 T c. The results in both cases indicate that at very high temperatures the T 2-scaled trace anomaly increases with temperature in accordance with the predictions of HTLpt.
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