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Manuel Calder ó n de la Barca S á nchez

ISMD ‘02, Alushta, Ukraine Sep 9, 2002. Manuel Calder ó n de la Barca S á nchez. Understanding “Bulk” Matter in HI collisions. 99.5%. Studying Matter: Global Observables N ch ,  E T  ,  p T   e , S, … Particle Yields & Ratios  T ch , m B , m S , … Particle Spectra

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Manuel Calder ó n de la Barca S á nchez

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  1. ISMD ‘02, Alushta, Ukraine Sep 9, 2002 Manuel Calderón de la Barca Sánchez

  2. Understanding “Bulk” Matter in HI collisions 99.5% Studying Matter: • Global Observables Nch, ET, pT  e, S, … • Particle Yields & Ratios  Tch, mB, mS, … • Particle Spectra  Tfo, flow, stopping, … STAR preliminary

  3. Nch: Centrality Dependence at RHIC (SPS) _ pp PHOBOS Au+Au |h|<1 200 GeV 130 GeV Au+Au 19.6 GeV preliminary (preliminary) • Everything counts: • Nch|h=0 described nicely by Kharzeev-Nardi (hard + soft) • Nch scales with Npart

  4. ET/ Nch from SPS to RHIC PHENIX preliminary PHENIX preliminary Independent of centrality Independent of energy Surprising fact: SPS  RHIC: increased flow, all particles higher pT still ET/ Nch changes very little Does different composition (chemistry) account for that?

  5. pT of Charged Hadrons from SPS to RHIC increase only ~2% STAR preliminary Saturation model: J. Schaffner-Bielich, et al. nucl-th/0108048 D. Kharzeev, et al. hep-ph/0111315 Many models predict similar scaling (incl. hydro) Need data around s = 70 GeV to verify (or falsify)

  6. Ratios • Huge amount of results from all 4 RHIC experiments: • systematic studies of: p-/p+, K-/K+,p/p,/ ,/,/, p/p, K/p , /, /h, , /p, f/K, K*/K, … • many as function of pT, Npart • at s of (20), 130, and 200 GeV • Problem: with and without feed-down correction • BRAHMS  large y coverage and reach to high pT • PHENIX  reach to high pT • STAR multi-strange baryons

  7. Ratios at RHIC I : vs. p^ All experiments: p-/p+ 1 K-/K+ 0.95 Does p/p also stay constant, or does it begin falling?

  8. Ratios at RHIC II: vs. y BRAHMS 200 GeV At mid-rapidity: Net-protons: dN/dy  7 proton yield: dN/dy  29  ¾ of all protons from pair-production

  9. K-/K+ and p/p from AGS to RHIC Slightly different view of statistical model. Becattini calculation using statistical model: T=170, gs=1 (weak dependency) vary mB/T  K+/K- andp/p K- /K+=(p/p)1/4 is a empirical fit to the data points K-/K+ driven by ms ~ exp(2ms/T) p/p driven by mB ~ exp(-2mB/T) ms = ms (mB) since <S> = 0 BUT: Holds for y  0 (BRAHMS y=3)

  10. Rapidity Spectra: Boost-Invariance at RHIC ? D. Ouerdane (BRAHMS)

  11. Boost-Invariance at RHIC ? p- p- • dN/dy of pions looks boost-invariant BUT • change in slopes for rapidity already from 0  1 • BRAHMS (J.H. Lee): no change in proton slope from y = 0  3 BUT increase in dN/dy •  Boost invariance only achieved in small region |y|<0.5

  12. Identified Particle Spectra at RHIC @ 200 GeV BRAHMS: 10% central PHOBOS: 15% PHENIX: 5% STAR: 5% Feed-down matters !!!

  13. Interpreting the Spectra • The shape of the various particle spectra teach us about: • Kinetic freeze-out temperatures • Transverse flow • The stronger the flow the less appropriate are simple exponential fits: • Hydrodynamic models (a la Heinz/Kolb/Shuryak/Huovinen/Teaney) • Hydro inspired parameterizations (Blastwave) • Blastwave parameterization: • Ref. : E.Schnedermann et al, PRC48 (1993) 2462 (modifications by Snellings, Voloshin) • Very successful in recent months • Spectra • HBT (incl. the Rout/Rside puzzle) • Flow spectra (p) HBT b

  14. Blastwave Fits at 130 & 200 GeV Results depend slightly on pT coverage STAR: Tfo ~ 100 MeV bT ~ 0.55c (130) & 0.6c (200) PHENIX: Tfo ~ 110 MeV (200) bT ~ 0.5c (200) 200 GeV Fits M. Kaneta (STAR)

  15. What flows and when? <pT> prediction with Tth and <b> obtained from blastwave fit (green line) STAR <pT> prediction for Tch = 170 MeV and <b>=0 pp no rescattering, no flow no thermal equilibrium preliminary F. Wang  and  appear to deviate from common thermal freeze-out Smaller elast? Early decoupling from expanding hadronic medium? Less flow? What about partonic flow?

  16. Does it flow? Fits to Omega mT spectra STAR preliminary RHIC SPS/NA49 bT is not well constrained ! • What do we now about elast of  and  ? • May be it flows, and may be they freeze out with the others • Maybe  and  are consistent with a blastwave fit at RHIC • Need to constrain further  more data & much more for v2 of 

  17. Other Attempts: The Single Freeze-Out Model • Single freeze-out model (Tch=Tfo) • (W. Broniowski et. al) fit the data well (and reproduce f, K*, L, X, W) •  Thermal fits to spectra are not enough to make the point. • To discriminate between different models they have to prove their validity by describing: • Spectra (shape & yield) • Correlations (HBT, balance function, etc.) • Flow • Only then we can learn …

  18. Conclusions • Flood of data from SPS & RHIC • new probes • correlations between probes • higher statistics & precision • Models (Generators) are behind • The majority of models in RHI fail already describing global observables (possible exception AMPT) • Many models describe “A” well but fail badly at “B”  can still be useful but limited scope • We learn more by combing various pieces and putting them into context • Thermalization, Chemical and Kinetic Freeze-out Conditions, and System Dynamics can only be studied (and are studied) using all the pieces together • Agreement between thermal fits to particle spectra and ratios + flow makes a very strong case for thermalization of matter created at RHIC

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