1. Strong and Electroweak Matter, June 16, 2004 Manuel Calderón de la Barca Sánchez RHIC Collisions The road so far. RHIC Collisions The road so far.

2. 2 A little background @ Main goal of RHIC Heavy Ion program: H To search for QGP formation in the laboratory, and H To study the properties of this state of matter @ Today’s talk: H On the progress made in the last 3 years of RHIC H Present some of the striking measurements obtained at RHIC so far H Many open questions!! @ “RHIC Whitepapers”: H Critical evaluation of the data and its (possible) interpretation H Present questions to the (theory) community for open discussion H Hope: Reach a better assessment of the implications of these measurements and of the next steps

3. 3 The Relativistic Heavy Ion Collider STAR PHENIX PHOBOS BRAHMS RHIC Design PerformanceAu + Aup + p Max  s nn 200 GeV500 GeV L [cm -2 s -1 ]2 x 10 26 1.4 x 10 31 Interaction rates1.4 x 10 3 s -1 6 x 10 5 s -1 Two Superconducting Rings Ions: A = 1 ~ 200, pp, pA, AA, AB

4. 4 Suppression at high transverse momenta @ Suppression of particle yield is a final state effect! @ Consistent with expectations from parton energy loss in a dense medium @ Not consistent with predictions for initial state gluon saturation (Color Glass Condensate) at mid-rapidity. @ Compare yields in Au+Au to yields in pp by taking the ratio R @ Yield is suppressed in Au+Au @ It is not suppressed in d+Au

5. 5 Dissappearance of the back-to-back correlation @ In central Au+Au, the away side jet is strongly suppressed @ d+Au data do not show this! @ Back to back supression is a final state effect @ Consistent with expectations of parton energy loss in a dense medium

6. 6 Away-side suppression is larger out-of-plane compared to in-plane The back to back correlation depends on the average distance traveled through the medium! Geometry of dense medium imprints itself on correlations STAR Preliminary Geometry of away-side suppression

7. 7 High-p t : summary of 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

8. 8 Where does the jet go? Away side away side associated particle decreases with centrality, approaching medium hadron in central collisions equilibration between the two sources of particles

9. 9 Suppression phenomena @ The observed strong suppression can be described efficiently by parton energy loss in matter H Implication: large energy density, large gluon density @ Does the magnitude of the energy loss inferred from the measurements demand an explanation in terms of traversal through deconfined matter? H Does factorization still apply in medium? Do fragmentation functions get modified? H Does the treatment of energy loss in the expanding system amplify the uncertainties inherent in the above assumption? @ Can one prove that the densities require the formation of a deconfined system?

10. 10 Particle ratios and statistical models @ Chemical freeze-out ~ 170 MeV, close to expected T c @ Particle ratios similar in pp for most abundant species @ Deviations of the resonance yields compared to thermal model predictions H indicative of hadronic phase after chemical freeze-out STAR PHENIX Strangeness Enhancement Resonance Suppression

11. 11 Identified particle spectra

12. 12 Identified particle spectra @ Mass dependence of particle spectra described reasonably well by ideal hydrodynamics Hydro (P. Kolb & U. Heinz) With initial flow kick Central AuAu √s = 200 GeV

13. 13 Anisotropy parameter v 2 y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Initial/final conditions, dof, EOS

14. 14 “Elliptic flow” data Hydrodynamic limit STAR PHOBOS Hydrodynamic limit STAR PHOBOS Compilation and Figure from M. Kaneta First time in Heavy-Ion Collisions a system created which at low p t is in quantitative agreement with ideal hydrodynamic model predictions for v 2 up to mid-central collisions PHOBOS: Phys. Rev. Lett. 89, 222301 (2002) STAR: Phys. Rev. Lett. 86, 402 (2001) PHENIX: Phys. Rev. Lett. 89, 212301 (2002) RQMD

15. 15 v 2 (m,p t ) @ Hydro calculation constrained by particle spectra @ Clear mass dependence; signature of collective flow (not only in hydro) @ Dependence on particle mass: Hydrodynamics gives a natural description at low transverse momenta H Still some deviations of 20-30% Hydro calculations: Kolb, Heinz and Huovinen

16. 16 Thermalization @ Is the system in approximate local thermal equilibrium? @ Evidence: H Hydrodynamics successfully accounts for v2 and soft particle spectra (for the first time in HI collisions). W Indirectly points to a rapid thermalization W Comparison with data favors a soft equation of state. H Statistical approach to particle ratios: excellent agreement with data W Tch = 170 MeV ~ Tc : lower limit W Assumes thermal equilibrium for its applicability, does not prove it. @ How do we know that the observed elliptic flow can not result alternatively from a harder EOS coupled with incomplete thermalization? H D. Teaney, J. Lauret, E.V. Shuryak; Phys. Rev. Lett 86, 4783 (2001)

17. 17 Space-Time information: HBT correlations @ HBT “radii” show an azimuthal dependence; qualitative centrality dependence fits into picture obtained from v 2 and spectra R side 2

18. 18 Space-time Information: the oddball @ Dynamical models which succeed with spectra and elliptic flow give a rather poor description of the HBT “radii” @ Observables like elliptic flow are an integral over the time evolution H this seems to be not very well under control

19. 19 HBT, spectra and v 2 ; the soft sector @ The argument for the success of hydro: @ Resting on key soft-physics observables H The magnitude and centrality dependence of v2 H Hadron mass-dependence of v 2 to the EOS @ How does the level of this EOS sensitivity compare quantitatively to that of uncertainties in the calculations? H Range of adjustable parameters: what is the uncertainty, and predictive power? H Failure to describe the spectra, elliptic flow and HBT at the same time

20. 20 Identified particles at intermediate to high-p t @ Two groups, baryons and mesons @ Are the valence quarks the relevant scaling? @ Coalescence/recombination provides an elegant description between 1.5- 6 GeV/c

21. 21 Fragmentation + Recombination Fragmentation Recombination Bass et al. nucl-th/0306027 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]

22. 22 Does it fit the measured spectra? T eff = 350 MeV blue- shifted temperature pQCD spectrum shifted by 2.2 GeV R.J. Fries, B. Müller, C. Nonaka, S.A. Bass; PRL 90 202303 (2003)

23. 23 D. Molnar, S.A. Voloshin Phys. Rev. Lett. 91, 092301 (2003) V. Greco, C.M. Ko, P. Levai Phys. Rev. C68, 034904 (2003) R.J. Fries, B. Muller, C. Nonaka, S.A. Bass Phys. Rev. C68, 044902 (2003) Coalescence Coalescence, recombination work at intermediate p  Au+Au  s NN =200 GeV

24. 24 Quark coalescence: Au+Au  s NN =200 GeV STAR Preliminary MinBias 0-80% Works for: K 0 s (sd)  (sdu)  (ssd)  Partonic flow  v 2 s ~ v 2 u,d ~ 7%

25. 25 Identified particles at intermediate to high-p t @ Baryon-meson scaling: importance of constituent quark d.o.f H Suggestive of collective flow at constituent quark level @ Scaling is naturally accomodated in a coalescence/recombination picture @ Would like to see predictions for future measurements: H Centrality dependence? H Correlations between mesons-baryons? H Does it work if one incorporates a more complete space-time evolution?

26. 26 First D Measurement at RHIC  D 0, D , D* spectra from d+Au  Cover range 0.2 < p T < 11 GeV/c  Necessary baseline for Au+Au

27. 27 Heavy Flavor D,B  e + X  (e + + e - )/2 spectrum, background subtracted  e-PID by TOF, dE/dx and EMC, measurements consistent  Consistent with measured D meson yield  PYTHIA:c  e, dominates at p T ~ 2-4 GeV/c b  e, dominates at p T > 4-5 GeV/c

28. 28 Summary, and the road ahead High p t  consistent with jet quenching scenario Bulk properties: rapid thermalization, soft EOS Hydrodynamics works well for spectra and v2, but not for HBT. v 2, R AB  quark coalescence seems to work, 2-4 GeV/c  partonic collectivity ? Significant progress in our understanding of the matter produced in the collisions!

29. 29 …and the road ahead Study various particles: centrality dependence of spectra and v 2 of d,  0, , , ,…, Heavy flavor production analysis is just getting started J/ ,  ’, maybe  … better probes of deconfinement? So far, no evidence whatsoever of chiral symmetry restoration Does it occur? And can we measure it? What is the best way? RUN 4 : An order of magnitude more data… with more complete detectors!  s NN = 200 GeV, 62.4 GeV