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

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

Nch: Centrality Dependence at RHIC (SPS) PHOBOS Au+Au |h|<1 200 GeV 130 GeV Au+Au _ pp 19.6 GeV preliminary (preliminary) pp not in fit fix point 1.5 off beam-rapidity Everything counts: Nch|h=0 described nicely by Kharzeev-Nardi (hard + soft) Nch scales with Npart

ET/ Nch  from SPS to RHIC PHENIX preliminary PHENIX preliminary Hagedorn 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?

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)

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

Ratios at RHIC I : vs. p^ All experiments: p-/p+  1 K-/K+  0.95 3x more protons produced than shifted in from beam Does p/p also stay constant, or does it begin falling?

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

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 Kristoph Redlich : two different curves: AGS K/K driven by associate production / RHIC pair production BUT: Holds for y  0 (BRAHMS y=3)

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

Boost-Invariance at RHIC ? p- p- MB fits 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

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

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 Increasing T has similar effect on a spectrum as increasing b But it has opposite effect on R(pT) opposite parameter correlations in the two analyses  tighter constraint on parameters spectra (p) HBT b

Blastwave Fits at 130 & 200 GeV 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)

What flows and when? STAR <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 fit k, pi, p only ---- <pt> Boltzman for pion, K exp, p exponential, rest is exponential  and  appear to deviate from common thermal freeze-out Smaller elast? Early decoupling from expanding hadronic medium? Less flow? What about partonic flow?

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 

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 …

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