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Isotropization of an equilibrating Quark-Gluon Plasma
Bin Zhanga, Lie-Wen Chenb, Che-Ming Koc
aArkansas State University, bShanghai Jiaotong University, cTexas A&M University24th 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.).
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The AMPT model
Lin et al, PRC 72, 064901 (2005)
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The AMPT model
Chen et al.,PLB605,95(2005)
Chen et al.,PRC69,031901(2004)
Good description of light hadron low pT spectra and elliptic flow
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Bulk properties in the AMPT model
Equation of state can be characterized by P/ε as a function of ε.
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 <m>/<K.E.> 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
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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
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The AMPT model
Rapidity distributionsHBT radii
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Pressure anisotropy in the AMPT model
Comoving frame is necessary even for |ηs|<0.5
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
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Bulk Properties including free streaming hadrons