# Presentation: 868364

## 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 QCD, 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

- 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 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)

## 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

## 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!