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Toward parton equilibration with improved parton interaction matrix elements

Toward parton equilibration with improved parton interaction matrix elements. Bin Zhang Arkansas State University The 11 th International Conference on Nucleus-Nucleus Collisions San Antonio, Texas, May 27 – June 1, 2012. Introduction Pressure anisotropy and energy density

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Toward parton equilibration with improved parton interaction matrix elements

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  1. Toward parton equilibration with improved parton interaction matrix elements Bin Zhang Arkansas State University The 11th International Conference on Nucleus-Nucleus Collisions San Antonio, Texas, May 27 – June 1, 2012 • Introduction • Pressure anisotropy and energy density • gg <-> ggg with the exact matrix element • Summary and speculations Work supported by the U.S. National Science Foundation under Grant No. PHY-0970104

  2. Introduction: radiative transport • The reaction rates

  3. Longitudinal to transverse pressure ratio Lines (points): exponential (condensate) initial conditions • competition between expansion and equilibration • common asymptotic evolution • more isotropization with inelastic processes • not sensitive to initial momentum distribution with inelastic processes

  4. Exact matrix element for gg↔ggg Propagators regulated by μ2 When αs=0.47, μ2=10 fm-2, s=4 GeV2, σ22=0.312 fm2, and σ23=0.0523 fm2. σ23/σ22~0.168 (When αs=0.3, μ2=6.38 fm-2, s=4 GeV2, σ22=0.199 fm2, and σ23=0.0504 fm2.)

  5. Exact matrix element vs. Gunion-Bertsch singularity regulated by μ2 Gunion-Bertsch Gunion-Bertsch Gunion-Bertsch f exact f f exact exact φ φ

  6. Exact matrix element for gg↔ggg When αs=0.47, μ2=10 fm-2, I32=6.84 fm2. Estimate with isotropic matrix element gives I32=6.19 fm2. When αs=0.47, μ2=10 fm-2, I32=4.85 fm2. Estimate with isotropic matrix element gives I32=6.19 fm2. E=0.344 GeV 0.728 0.691 0.626 0.682 0.928

  7. Summary and speculations • Elastic collisions may be more important in thermalization than expected. • Specific shear viscosity may be larger than the quantum limit. • Formation time regularization can be approximated by screening mass regularization (replacement of the theta function by a Lorentzian). • Exact and Gunion-Bertsch can have big differences. • Bethe-Heitler limit may be important for bulk matter thermalization (formation time vs. mean free path). • Elastic collisions can also be important for heavy quark equilibration (meson dissociation).

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