Thermalization of gluons at RHIC: Dependence on initial conditions

Xu, Zhe; Greiner, Carsten

doi:10.1140/epja/i2005-10294-8

“…The quick thermalization and the smallness of the η/s ratio observed in the present calculations with the CGC initial conditions are consistent with the findings from the previous studies [5,6,13,28,29] using the Glauber-type minijets initial conditions. This demonstrates that independent of the chosen initial conditions, the pQCD bremsstrahlung processes (and the back reactions) dominate the dynamical equilibration and then keep the system behaving like a nearly perfect fluid.…”

Section: Discussionsupporting

confidence: 93%

“…Therefore, the time scale of thermalization is of order α −2 s (ln α s ) −2 Q −1 s , which is smaller than the "Bottom-Up" prediction. The quick thermalization observed here is consistent with the findings from the previous studies [5,6,13]: The gluon bremsstrahlung favors initial condition with α s = 0.2 and Q s = 3 GeV could be appropriate for Pb-Pb collisions at the maximal energy at the LHC. In this case the gluon number also decreases at the beginning.…”

Section: Time Scale Of Thermalizationsupporting

confidence: 91%

Thermalization of a color glass condensate and review of the “bottom–up” scenario

El¹,

Xu²,

Greiner³

2008

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The thermalization of a longitudinally expanding color glass condensate with Bjorken boost invariant geometry is investigated within microscopical parton cascade BAMPS. Our main focus lies on the detailed comparison of thermalization, observed in BAMPS with that suggested in the "Bottom-Up" scenario. We demonstrate that the tremendous production of soft gluons via gg → ggg, which is shown in the "Bottom-Up" picture as the dominant process during the early preequilibration, will not occur in heavy ion collisions at RHIC and LHC energies, because the back reaction ggg → gg hinders the absolute particle multiplication. Moreover, contrary to the "Bottom-Up" scenario, soft and hard gluons thermalize at the same time. The time scale of thermal equilibration in BAMPS calculations is of order α −2 s (ln α s ) −2 Q −1 s . After this time the gluon system exhibits nearly hydrodynamical behavior. The shear viscosity to entropy density ratio has a weak dependence on Q s and lies close to the lower bound of the AdS/CFT conjecture.

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“…The quick thermalization and the smallness of the η/s ratio observed in the present calculations with the CGC initial conditions are consistent with the findings from the previous studies [4,5,12,16,17] using the Glauber-type minijets initial conditions. This demonstrates that independent of the chosen initial conditions, the pQCD bremsstrahlung processes (and the back reactions) dominate the dynamical equilibration and then keep the system behaving like a nearly perfect fluid.…”

Section: Discussionsupporting

confidence: 93%

“…The dependence on α s proves to be weaker than the "Bottom-Up" prediction but consistent with the scaling obtained in [16]. The reason for the quick thermalization observed in our calculations is the gluon bremsstrahlung, which favors large-angle radiation due to the LPM suppression [4,5,12]. Thus, the pQCD gg ↔ ggg processes are dominant for the thermal equilibration.…”

Section: Introductionsupporting

confidence: 87%

Thermalization of a color glass condensate and review of the ‘bottom-up’ scenario

El¹,

Greiner²,

Xu³

2008

J. Phys. G: Nucl. Part. Phys.

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The thermalization of a longitudinally expanding color glass condensate with Bjorken boost invariant geometry is investigated within microscopical parton cascade BAMPS. Our main focus lies on the detailed comparison of thermalization, observed in BAMPS with that suggested in the "Bottom-Up" scenario. We demonstrate that the tremendous production of soft gluons via gg → ggg, which is shown in the "Bottom-Up" picture as the dominant process during the early preequilibration, will not occur in heavy ion collisions at RHIC and LHC energies, because the back reaction ggg → gg hinders the absolute particle multiplication. Moreover, contrary to the "Bottom-Up" scenario, soft and hard gluons thermalize at the same time. The time scale of thermal equilibration in BAMPS calculations is of order α −2 s (ln α s ) −2 Q −1 s . After this time the gluon system exhibits nearly hydrodynamical behavior. The shear viscosity to entropy density ratio has a weak dependence on Q s and lies close to the lower bound of the AdS/CFT conjecture.

show abstract

“…In [2] it is demonstrated that the inelastic processes dominate the total transport collision rate and thus contribute much stronger to momentum isotropization then elastic ones. Within a default setting of minijet initial conditions, the overall build up of elliptic flow v 2 can be reasonably described [4] (a more dedicated study is presently undertaken [5]).…”

mentioning

confidence: 99%