2. Outline First of all, there’s too much data!! BRAHMS PHOBOS PHENIX
Focus on some recent results and analyses
BRAHMS
PHOBOS
PHENIX
STAR
Low, Intermediate, High-pt
Can we understand it? Can at least some of it be synthesised?
Spectra
Flow

3. Particle Spectra in Au+Au, STAR |y|<.5
STAR Preliminary
Hydro inspired “Thermal” Fits (input to Blast-Wave parameterization) (T, bt) = (170 MeV, 0.6c) Large transverse flow component in central collisions.

4. Hydrodynamics  Equation of State
Low pt, 99.5% of particles are below 2 GeV.
Hydrodynamics describes bulk particle momentum distributions
Hydro is limit of zero mean free path…early phase dominated by strong interactions?
Calculations  too long a system lifetime (still work to do)
Enormous initial pressure, but decouples quickly (~10 fm/c)

5. Spectra at large y, BRAHMS.
Radial flow decreases
at large rapidity.
Boost invariant region is only
about 1 unit wide! 3-D hydro
y=0 Thermal fit
T = 0.53
T = 138. MeV
y=3 Thermal fit
T = 0.42
T = 140 MeV

6. Charged hadrons at large h, PHOBOS
T. Hirano
Hydrodynamics:
Mid-rapidity data is well described, but larger rapidity is not.

7. Particle Ratios and Statistical Models
Statistical models do a very good job.
Values Tch are very close to expected Tcrit from lattice.
However, this alone cannot prove a phase transition nor that the system is thermal; but coupled with agreement from hydrodynamics (spectra and v2), evidence starts to increase…

8. Intermediate pt, spectra for various masses
Yield of p (L) similar to p(K) at ~3 GeV, flow effect for heavier
particle/baryon?

9. Compare with scaling by Ncoll…
K0s and p0 show suppression at 2-3 GeV, p and L do not… strong radial flow for heavier particles?

10. Particles with Similar Mass
Differ at low pt, similar at ~3 GeV
Reflection of Flow? Rescattering? Recombination?
Rescattering has effect on other observables: resonances! (See Patricia’s talk)

11. Wealth of data!
It is very important to try to understand as much of the combined measurements as possible
Under a single framework!
Many times, predictions work for observable A but fail for observable B. Need a coherent picture!
Some recent ideas:
Hydro-inspired Blast-wave (won’t go into it)
Recombination+Fragmentation
Single Freeze-out

12. Fragmentation + Recombination
Lopez, Parikh, Siemens, PRL 53 (1984) 1216:
Net charge and baryon number fluctuations [Asakawa, Heinz, BM, PRL 85 (2000) 2072; Jeon, Koch, PRL 85 (2000) 2076]
Balance functions [Bass, Danielewicz, Pratt, PRL 85 (2000) 2689]
Recombination / coalescence [Fries, BM, Nonaka, Bass, nucl-th/ ; Greco, Ko, Levai, nucl-th/ ; Molnar, Voloshin, nucl-th/ ]
Fragmentation
Recombination
Bass et al. nucl-th/

13. F+R: Model assumptions
at low pt, quarks and antiquarks recombine into hadrons locally “at an instant”:
hadron momentum P is much larger than average momentum Δp2 of the internal quark wave function of the hadron;
features of the parton spectrum are shifted to higher pt in the hadron spectrum
parton spectrum has thermal part (quarks) and a power law tail (quarks and gluons) from pQCD.

14. Does it fit the measured spectra?
Teff = 350 MeV blue-shifted temperature
pQCD spectrum shifted by 2.2 GeV
R.J. Fries, B. Müller, C. Nonaka, S.A. Bass; PRL (2003)

15. For identified particles…p, K

16. …p, f, L, X, W

17. Ratios vs pt

18. High pt suppression.
Reproduces charged hadron suppression, and flavor dependence.
Prediction, quenching for protons above 6 GeV, where fragmentation starts to dominate

19. What about v2?

20. Does v2 reflect partonic flow?
P. Sorensen (UCLA – STAR)
Quark v2
Recombination model suggests that hadronic flow reflects partonic flow (n = number of valence quarks):
Provides measurement of partonic v2 !
See also: Lin & Ko, PRL 89 (2002) ; Molnar & Voloshin, nucl-th/

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

22. Single freeze-out model, Tch = Tkin?
Very nice feature, include
feeddown in the calculations.
Describe spectra and ratios
vs pt and vs centrality well
Supports the use of thermal approach to heavy ion collisions
If Tch=Tkin, very explosive expansion!
W. Broniowski and W. Florkowski, PRC (2002), for 130 GeV
A. Baran, W. Broniowski, W. Florkowski nucl-th/ for 200 GeV ratios and spectra.

23. High-pt: Latest news from the d+Au run
From cover of
PRL 91 (2003)
Phobos
Phenix
Star
Brahms
In Au+Au, suppression of high-pt hadrons and of away side jet, not seen in d+Au. Final state effect…consistent with the production of dense matter!!

24. Summary & Conclusions
All 4 RHIC experiments have continued their outpour of measurements.
Low pt spectra, hydrodynamic fits, statistical models taken together yield support (albeit don’t prove) to a high density thermalized phase.
Still trouble in the longitudinal direction (HBT, v2 vs y)
We are beginning to see more theoretical efforts that encompass various observables! That is good!
Spectra, flow, correlations. Would like to understand in one picture, pt, y and centrality dependence.
Fragmentation + Recombination: aplicability of the recombination regime to 3-6 GeV, fragmentation dominates at a higher pt than one naïvely expected.
v2 of hadrons reflects v2 of constituent quarks (? and !)
High-pt spectra and correlations: suppression of hadrons and away-side jet is a final state effect.