Isotropization of an equilibrating QuarkGluon Plasma

1
Isotropization of an equilibrating Quark-Gluon
Plasma

• Bin Zhanga, Lie-Wen Chenb, Che-Ming Koc
• aArkansas State University, bShanghai Jiaotong
  University, cTexas AM University
• 24th Winter Workshop on Nuclear Dynamics, South
  Padre Island, April 5-12, 2008

• The AMPT model
• Evolution of bulk properties in the AMPT model
• Pressure Anisotropy in the AMPT model
• Summary

Work supported by the National Science Foundation
under Grant PHY-0554930 (B.Z.) PHY-0457265, the
Welch Foundation Grant No. A-1358 (C.M.K.), the
NNSF of China Grant Nos. 10575071 and 10675082,
MOE of China project NCET-05-0392, Shanghai
Rising-Star Program Grant No. 06QA14024, and the
SRF for ROCS, SEM of China (L.W.C.).
2
The AMPT model
Lin et al, PRC 72, 064901 (2005)
3
The AMPT model
Chen et al.,PLB605,95(2005)
Good description of light hadron low pT spectra
and elliptic flow
Chen et al.,PRC69,031901(2004)
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Bulk properties in the AMPT model
Equation of state can be characterized by P/e as
a function of e. Active particle contributions
are evaluated.

• default model hadronizes earlier than the string
  melting model
• equation of state depends on the parton
  scattering cross section

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Bulk properties in the AMPT model
hadron ltmgt/ltK.E.gt increases
Strange percentage increases
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Pressure anisotropy in the AMPT model
Momentum isotropy can be characterized by PL/PT

• String melting scenario increases faster than
  the default scenario
• There is a late time increase to above 1. It is
  caused by on set of transverse expansion
• Larger parton cross section leads to larger
  early pressure anisotropy and late transverse
  expansion
• Partial thermalization is achieved

7
Summary and Outlook

• Pressure to energy density ratio in default model
  is much smaller than the string melting model
  over a wide range of energy density.
• Pressure to energy density ratio in the string
  melting model depends on the partonic cross
  section.
• Both longitudinal expansion and transverse
  expansion can affect pressure anisotropy
  evolution.
• The hot and dense matter in the AMPT model does
  not reach full isotropization.
• Effects of parton number changing processes,
  plasma instabilities, hadronization at fixed
  time, mean field deserve further study.

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The AMPT model
String melting is needed for the description of
elliptic flow
9
The AMPT model
Rapidity distributions
HBT radii
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Pressure anisotropy in the AMPT model
Comoving frame is necessary even for
?slt0.5 Mid-space-time rapidity region is boost
invariant
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Pressure anisotropy in the AMPT model
Parton recombination can introduce dependence on
space-time rapidity range
12
Bulk Properties including free streaming hadrons