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. Olga Barannikova Berkeley School, May 20052 Bulk properties – “Soft Physics” Spectral shapes: kinetic freeze-out properties transverse radial flow T kin @ kinetic freeze-out  different behavior? Flavor composition: chemical freeze-out properties T ch @ chemical freeze-out strangeness production strangeness enhancement? Resonance production: regeneration and rescattering K*,  (1520),  Motivation

3. Olga Barannikova Berkeley School, May 20053  Topological method dE/dx method Particle Identification K + K _ K(892)   + K  (1020)  K + K  (1520)  p + K K 0 s   +     + p   +  

4. Olga Barannikova Berkeley School, May 20054 K    K0sK0s  K* Variety of hadron species:                pp, Au+Au, d+Au Same experimental setup! Transverse mass spectra STAR Preliminary

5. Olga Barannikova Berkeley School, May 20055 Statistical Model Fit Stable p a rticle ratios well described with T ch = 160  10 MeV,  B = 24  5 MeV Thermalization ?

6. Olga Barannikova Berkeley School, May 20056 Chemical Freeze-out Properties ,K,p ,K,p,  Close to chemical equilibrium ! Close to net-baryon free

7. Olga Barannikova Berkeley School, May 20057 E.Schnedermann et al, PRC48 (1993) 2462. whereand Blast-wave model: Spectral shapes T dec = 100 MeV Common hydro description ? Kolb and Rapp, PRC 67 (2003) 044903. Sudden Single Freeze-out ? A. Baran et al.; nucl-th/0305075. , K, p  T= 90MeV,   T=160MeV, 

8. Olga Barannikova Berkeley School, May 20058 -- K-K- T=160MeV  , K, p   c Fit details -- K-K- , K, p  T= 90MeV,  c

9. Olga Barannikova Berkeley School, May 20059 Resonance effects? -- p , GeV/c K-K- Thermal model :  One freeze-out T chem = T kin = 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

10. Olga Barannikova Berkeley School, May 200510   /dof  2 BW fit with Resonances More complete study of resonance effects: code from U.A.Wiedemann, U.Heinz, PRC 56 (1997), 3265   /dof  6   /dof  2

11. Olga Barannikova Berkeley School, May 200511 Other RICH experiments? -- K-K- pp pp  PHENIX  STAR  PHOBOS -- K-K-  PHENIX+PHOBOS+STAR  T= 96 MeV,  c  Consistent BW results * STAR only

12. Olga Barannikova Berkeley School, May 200512  Sudden Single Freeze-out ?* Kinetic Freeze-out Radial flow velocity Kinetic FO temperature ,K,p: T kin decreases with centrality  T kin = const ,  and  flow

13. Olga Barannikova Berkeley School, May 200513 TcTcTcTc T kin ~ 90 MeV,  ~ 0.6 T kin ~ T ch ~ 160 MeV   ~ 0.45 rescattering Partonic flow? Freeze-out Evolution Lattice QCD: T c = 170  10 MeV  Chemical FO close to hadronization  Strong flow at hadronization

14. Olga Barannikova Berkeley School, May 200514 Time Scale T ch  T kin For massless particles in equilibrium: Entropy density ~ T 3

15. Olga Barannikova Berkeley School, May 200515 Resonance Production and Survival time T ch Yields time Hadrongas Chemical FO Kinetic FO T kin Spectra pp –No extended initial medium –Chemical freeze-out –Kinetic freeze-out close to the Chemical freeze-out Au + Au –Extended hot and dense phase –Thermalization & Chemical freeze-out –Kinetic and Chemical freeze-outs are separated 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 Dense medium Hadronization Chemical FO Kinetic FO lost measured   K K*K* K K*K* K*K*  K   K*K* K K

16. Olga Barannikova Berkeley School, May 200516 in Au + Au at 200 GeV in Au + Au at 200 GeV K* ++++  increase from pp to Au+Au: Proton (GeV/c) Centrality 0.760  0.0501.030  0.120 50% - 80% 0.620  0.0400.680  0.040 pp 1.090  0.1101.080  0.120 0% - 10% K(892) (GeV/c) Signal loss of ~70% for K* Signal loss at low p T : UrQMD: signal loss at low p T due to rescattering of decay daughters  is higher UrQMD has long lifetime (  5-20fm/c)

17. Olga Barannikova Berkeley School, May 200517 Resonances and Stat. Model Strangeness Enhancement Resonance Suppression  In pp particle ratios are well described  In Au+Au only stable particle ratios are well described

18. Olga Barannikova Berkeley School, May 200518 M. Bleicher et al. J. Phys. G 25 (1999) 1859 σ(Kπ) σ(ππ) Rescattering and regeneration is needed ! Life time [fm/c] :  = 40  = 13 K* = 4  ++ = 1.7 Resonance ratios modified from pp to Au+Au Rescattering and regeneration is needed !  > 4 fm/c (lower limit) Thermal model UrQMD Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and Horst Stöcker.Phys.G30 (2004) 111. K*   + K   K + K   p + K  ++   p  + Ratios

19. Olga Barannikova Berkeley School, May 200519 Chemical Freeze-out conditions:  Particle ratios suggest equilibrium  Invariant T ch ~160 MeV ~ T C -near lattice phase boundary  Thermal model does not reproduce resonances Kinetic freeze-out conditions:  , K,p vary with centrality : T kin ,   Collectivity (strong flow) builds up very early  Multistrange baryons: T kin ~ T ch Between freeze-outs:  Chemical  kinetic :  ~6 fm/c – Resonances are strongly affected by rescattering –  >4 fm/c rescattering-based estimate – in agreement with blast wave results – Summary

20. Olga Barannikova Berkeley School, May 200520 -- K-K- pp  PHENIX  STAR  PHOBOS  T = 90 MeV  T = 160 MeV Open Questions and a Wish List Hydro, Statistical Model pTpT 2-3 GeV/c6-7 GeV/c0 SoftHard Intermediate pQCD, Fragmentation Jet quenching ?? pp  T = 90 MeV  T = 160 MeV T = 87 MeV T = 101 MeV T = 109 MeV pp -- STAR Preliminary Applicability limits? Theoretical models for extended momentum range