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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