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

Outline

Introduction SPheRIO Chemical freeze-out Numerical Result Conclusion

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

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 Q

CD, Quasiparticle Model…

Freeze-out Chemical/thermal, Continuous emission, Partial chemical

equilibrium, Cascade model...

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?

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

IC: NEXUS event generator

Initial condition Hydrodynamic equations Equation of state Freeze out and particle emission

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

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

Lattice size dependence

Chemical freeze-out in SPheRIO Hyperons ΛΞΩ and anti-proton undergo che

mical 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)

Numerical Results

Event by event fluctuation initial condition(average over 100 events)

Up left:

Pseudo-rapidity distribution

Up right:

Pt districution for all charged particlesUsed to fit thermal freeze-out temperature

Right:

Pt distribution for ΛUsed to fit chemical freeze-out temperature

Numerical Results

Numerical Results

Numerical Results

Numerical Results

Numerical Results

Numerical Results

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

Thank you!谢谢 !