Outline

2. Outline • First of all, there’s too much data!! • 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. y=3 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 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/0301087; Greco, Ko, Levai, nucl-th/0301093; Molnar, Voloshin, nucl-th/0302014] Bass et al. nucl-th/0306027

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? R.J. Fries, B. Müller, C. Nonaka, S.A. Bass; PRL 90 202303 (2003) pQCD spectrum shifted by 2.2 GeV Teff = 350 MeV blue-shifted temperature

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? Recombination model suggests that hadronic flow reflects partonic flow (n = number of valence quarks): P. Sorensen (UCLA – STAR) Quark v2 Provides measurement ofpartonicv2 ! See also: Lin & Ko, PRL 89 (2002) 202302; Molnar & Voloshin, nucl-th/0302014

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 65 064905 (2002), for 130 GeV A. Baran, W. Broniowski, W. Florkowski nucl-th/0305075 for 200 GeV ratios and spectra.

23. High-pt: Latest news from the d+Au run • 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!! From cover of PRL 91 (2003) 072302 Phobos 072303 Phenix 072304 Star 072305 Brahms

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.