Bulk properties at RHIC

1
Bulk properties at RHIC

• Olga Barannikova
• (Purdue University)

• Motivation
• Freeze-out properties at RHIC
• STAR perspective
• STAR ?PHENIX, PHOBOS
• Time-span estimates
• Summary and Open Questions

2
Motivation

• Bulk properties Soft Physics
• Spectral shapes
• kinetic freeze-out properties
• transverse radial flow
• Tkin _at_ kinetic freeze-out
• X,W,f different behavior?
• Flavor composition
• chemical freeze-out properties
• Tch _at_ chemical freeze-out
• strangeness production
• strangeness enhancement?
• Resonance production
• regeneration and rescattering
• K, L(1520), f

Partonic collectivity
Thermalization
Time span
3
Particle Identification
dE/dx method
K K_
Topological method
K
K(892) ? ? K ? (1020) ? K K ?(1520) ?
p K
K0s ? ? ? ? ? p p X
? L p
4
Transverse mass spectra
X
STAR Preliminary
Variety of hadron species K? , K0s, K, ?, ?,
?, ?, ?(1520), S(1385), X(1530), ?? , p, D pp,
AuAu, dAu Same experimental setup!
5
Statistical Model Fit
200 GeV AuAu

• Stable particle ratios well described with
• Tch 160?10 MeV,
• mB 24 ?5 MeV
• Thermalization ?

6
Chemical Freeze-out Properties
200 GeV AuAu
Close to net-baryon free
p,K,p
Close to chemical equilibrium !
p,K,p,L,X
7
Spectral shapes
Blast-wave model
E.Schnedermann et al, PRC48 (1993) 2462.
?, K, p ? T 90MeV, b0.6 X, ? ?
T160MeV, b0.45
Common hydro description ? Kolb and Rapp, PRC 67
(2003) 044903. Sudden Single Freeze-out ? A.
Baran et al. nucl-th/0305075.
8
Fit details
9
Resonance effects?

• Thermal model
• One freeze-out Tchem Tkin T
• Complete treatment of hadronic states
• Boost-invariance at mid rapidity
• T, ?B - fixed by ratios, ?, ? - fixed by p?-
  spectra
• W. Broniowski, et al, nucl-th/0305075

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BW fit with Resonances
??/dof ? 6

• More complete study of resonance effects code
  from
• U.A.Wiedemann, U.Heinz, PRC 56 (1997), 3265

??/dof ? 2
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Other RICH experiments?

• STAR only

• PHENIXPHOBOSSTAR ? T 96 MeV, b0.57 c
• Consistent BW results

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Kinetic Freeze-out
Kinetic FO temperature

• Sudden Single Freeze-out ?

Radial flow velocity

• p,K,p Tkin decreases with centrality
• X Tkin const
• ?, X and W flow

13
Freeze-out Evolution
Lattice QCD Tc 170?10 MeV

• Chemical FO close to hadronization
• Strong flow at hadronization

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Time Scale
Tch ? Tkin For massless particles in
equilibrium Entropy density T3
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Resonance Production and Survival

• pp
• No extended initial medium
• Chemical freeze-out
• Kinetic freeze-out close to the Chemical
  freeze-out

pp

• AuAu
• Extended hot and dense phase
• Thermalization Chemical freeze-out
• Kinetic and Chemical freeze-outs are separated

Tch Yields
Tkin Spectra
time

• Resonances
• Two competing effects regeneration and
  rescattering can change yields after chemical
  freeze-out
• Ratio to stable particle reveals information
  time-span between Chemical and Kinetic FO

time
AuAu
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ltpTgt in AuAu at 200 GeV
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Resonances and Stat. Model
200 GeV pp
200 GeV AuAu

• In pp particle ratios are well described
• In AuAu only stable particle ratios are well
  described

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Ratios
Life time fm/c ? 40 L 13 K
4 ? 1.7
K ? ? K ? ? K K ? ? p
K ? ? p p

• Resonance ratios modified from pp to AuAu
• Rescattering and regeneration is needed !
• ?? gt 4 fm/c (lower limit)

Rescattering and regeneration is needed !
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Summary

• Chemical Freeze-out conditions
• Particle ratios suggest equilibrium
• Invariant Tch 160 MeV TC -near lattice phase
  boundary
• Thermal model does not reproduce resonances
• Kinetic freeze-out conditions
• p,K,p vary with centrality Tkin ?, b?
• Collectivity (strong flow) builds up very early
• Multistrange baryons Tkin Tch
• Between freeze-outs
• Chemical ? kinetic Dt 6 fm/c
• Resonances are strongly affected by rescattering
• Dt gt4 fm/c rescattering-based estimate in
  agreement with blast wave results

20
Open Questions and a Wish List
Applicability limits?
Theoretical models for extended momentum range