Wei-Liang Qian University of São Paulo

1. A hydro approach to chemical freeze-out for identified particle spectra at 200AGeV Au-Au collisions at RHIC Wei-Liang Qian University of São Paulo

2. Outline • Introduction • SPheRIO • Chemical freeze-out • Numerical Result • Conclusion

3. Introduction • Success of hydro: single particle spectra and strong collective flow patterm • Building blocks for hydro model • Themal model fits for chemical/thermal freeze-out temperatures

4. Building blocks for hydro • Initial condition: • Glauber type, event generator, CGC , pQCD + saturation model… • EOS • Hadron gas, 1st phase transition, Bag Model, EoS based on Lattice QCD, Quasiparticle Model… • Freeze-out • Chemical/thermal, Continuous emission, Partial chemical equilibrium, Cascade model...

5. Chemical/thermal freeze-out • Chemical/thermal freeze-out temperature • Conclusions drawn from hydro-motivated model fits • Chemical freeze-out temperatures almost not depend on centrality • Strangeness saturation factor introduced as free parameter • Thermal freeze-out temperatures depend on centrality • Full 3+1 hydro with chemical freeze-out?

6. SPheRIO: SPH method • Smooth Particle Dynamics • Parameterize the matter flow in terms of discrete Lagrangian coordinates (namely, SPH particles) • EOM derived by variational principles in terms of SPH particle degree of freedom • Entropy is assigned to the SPH particle as a conserved quantity • Robustness to deal with any kind of geometrical structure

7. IC: NEXUS event generator • Initial condition • Hydrodynamic equations • Equation of state • Freeze out and particle emission

8. EOS with 1st order phase transition • Hadronic resonance model with finite volume correction for hadron phase, including main part of observed resonances in Particle Data Tables • Ideal gas model for QGP phase • Incorporate strangeness conservation • Local strangeness neutrality

9. Evolution of the fluid Space time evolution of one NEXUS event for most central collision Up left: Temperature profile on transverse plane Up right: Same diagram shown in 3-D axis Right: Matter flow on transverse plane

10. Lattice size dependence

11. Chemical freeze-out in SPheRIO • Hyperons ΛΞΩ and anti-proton undergo chemical freeze-out • Chemical/thermal freeze-out temperatures are fixed for most centrality and most peripheral windows • Interpolation for intermediate centrality windows • Fully strangeness equilibrium at CFO • Data from • Phys. Rev. C72, 014908 (BRAHMS) • Phys. Rev. Lett. 98, 062301(STAR)

12. Numerical Results Event by event fluctuation initial condition (average over 100 events) Up left: Pseudo-rapidity distribution Up right: Pt districution for all charged particles Used to fit thermal freeze-out temperature Right: Pt distribution for Λ Used to fit chemical freeze-out temperature

13. Numerical Results

14. Numerical Results

15. Numerical Results

16. Numerical Results

17. Numerical Results

18. Numerical Results

19. Conclusion • SPheRIO gives good panoramic description for the pt spectra for Au-Au 200 GeV • For light hadrons, no chemical freeze-out • Chemical freeze-out temperatures depend on centrality • Close to thermal freeze-out temperature

20. Thank you!谢谢!