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

2. 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

3. 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

4. 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?

5. pT of Charged Hadrons from SPS to RHIC
increase only ~2%
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)

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
3x more protons produced than shifted in from beam
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
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
Kristoph Redlich : two different curves: AGS K/K driven by associate production / RHIC pair production
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-
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  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
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

14. 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)

15. 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?

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