Spectra Physics at RHIC : Highlights from 200 GeV data Manuel Calderón de la Barca Sánchez ISMD ‘02, Alushta, Ukraine Sep 9, 2002

2 Understanding “Bulk” Matter in HI collisions Studying Matter:  Global Observables N ch,  E T ,  p T   , S, …  Particle Yields & Ratios  T ch,  B,  S, …  Particle Spectra  T fo, flow, stopping, … STAR preliminary 99.5%

3 N ch : Centrality Dependence at RHIC (SPS) _ pp PHOBOS Au+Au |  |< GeV preliminary 130 GeV 200 GeV Au+Au (preliminary) Everything counts: N ch |  =0 described nicely by Kharzeev-Nardi (hard + soft)  N ch  scales with N part

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

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

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

7 Ratios at RHIC I : vs. p  All experiments:      1 K  /K   0.95 Does  p/p also stay constant, or does it begin falling?

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

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

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

11 Boost-Invariance at RHIC ? 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 200 GeV Feed-down matters !!! BRAHMS: 10% central PHOBOS: 15% PHENIX: 5% STAR: 5%

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 l Spectra l HBT (incl. the R out /R side puzzle) l Flow spectra (  ) HBT

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

15 What flows and when? prediction with T th and obtained from blastwave fit (green line) prediction for T ch = 170 MeV and =0 pp no rescattering, no flow no thermal equilibrium STAR 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 m T spectra 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 v 2 of  SPS/NA49 RHIC STAR preliminary  T is not well constrained !

17 Other Attempts: The Single Freeze-Out Model Single freeze-out model (T ch =T fo ) (W. Broniowski et. al) fit the data well (and reproduce , K*, ,   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 l 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