Experimental Results at RHIC

1. Experimental Results at RHIC T. Hallman Brookhaven National Laboratory ISMD Kromeriz, Czech Republic August 9-15, 2005 TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

2. The Outline of this Talk • Brief definition of terms • Recent results on hard probes • Some thoughts about what the data are telling us • Conclusions TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

3. QGP  a (locally) thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes. • Not required: • non-interacting quarks and gluons • 1st- or 2nd-order phase transition • evidence of chiral symmetry restoration Definition of the terms QGP, v2, and RAA (RCP) TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

4. V2 (Elliptic Flow) z y x Anisotropic Flow py px Peripheral Collisions Comparison with hydro suggests early (local) thermalization of the matter and an EOS with a soft point Hydro calculations: Kolb, Heinz and Huovinen TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

5. leading particle suppressed hadrons q q ? Experimental Tools: High pT (Self-Analyzing) Probes of the Matter at RHIC Nuclear Modification Factor: <Nbinary>/sinelp+p nucleon-nucleon cross section AA If R = 1 here, nothing new going on RCP is the same construct with peripheral AA spectra as a reference TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

6. Partonic radiative energy loss in dense matter as a means to (indirectly) test deconfinement Thick plasma (Baier et al.): Gluon bremsstrahlung Thin plasma (Gyulassy et al.): • Linear dependence on gluon density glue: • measure DE  gluon density at early hot, dense phase • High gluon density requires deconfined matter • (“indirect” QGP signature !) TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

7. STAR Pedestal&flow subtracted An old story by now… Phys. Rev. Lett. 91, 072304 (2003). • In central Au+Au collisions: • Strong suppression of inclusive hadron production • Disappearance of the away-side jet • d+Au looks like p+p • Jet quenching in the dense medium • pQCD parton energy loss fits to observed central suppression  dNg/dy ~ 1000 at start of rapid expansion TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

8. What’s New for the Inclusives? Significantly higher PT • Partonic (vs hadronic) energy loss • Matter is surprisingly opaque • Should provide lower bound on dNg/dy System Size Systematics RAA for CuCu: same behavior for the same Npart as in AuAu, but better precision TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

9. Inclusive Suppression: RAA in Cu+Cu √sNN=200 GeV Au+Au A=197 Cu+Cu A=63 From Au+Au to Cu+Cu: change collision geometry in a more precise/ controlled way Result: Cu+Cu suppressed, but less so than Au+Au TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

10. Geometrical Dependence of RAA • RAA scales smoothly from Au+Au through Cu+Cu to p+ • Scaling prefers Npart1/3, though Npart2/3 not strongly excluded p+p TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

11. ? Limitations of RAA K.J. Eskola et al., NP A747, 511 • Leading hadrons preferentially arise from the surface • Limited sensitivity to the region of highest energy density • Need more penetrating probes RAA at 10 GeV/c Central RAA Data (~ strength of interaction) TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

12. Di-jets at much higher pT 8 < pT(trig) < 15 GeV/c pT(assoc)>6 GeV STAR Preliminary No background subtraction! Clear emergence of the away-side jet TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

13. Di-jets and the interaction mechanism Scaling factors relative to d+Au ~0.54 8 < pT(trig) < 15 GeV/c ~0.25 Direct measurement of the medium modification (and lack thereof) of the away-side jet • Away-side width and fragmentation function • Can partonic energy loss models describe these simultaneously? TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

14. X-N Wang, PLB 595, 165 (2004)  = STAR preliminary Di-jets and the medium Yield should provide the first upper limit on the density of the medium • Constrain the number of active degrees of freedom? [Müller, Rajagopal, hep-ph/0502174] 8 < pT(trig) < 15 GeV/c TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

15. 4.0 < pT(trig) < 6.0 GeV/c 2.5 < pT(trig) < 4.0 GeV/c 1.0<pT(assoc)<2.5 GeV/c 2.0<pT(assoc)<pT(trig) GeV/c 0.15<pT(assoc)<4.0 GeV/c How does the medium respond? Measure low-pT associated hadrons • Away-side particles increase in number and soften in pT • Away-side flat or small dip for intermediate pT(trig) STAR Preliminary TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

16. near Medium away Conical flow near Medium away Deflected jets Conical flow? • Does a shock wave form? • Three-particle correlations • Conical flow: associated particles may appear on opposite sides of Δφ = π • Deflected jets: associated particles on the same side of Δφ = π Df2 Df1 Df2 Casalderrey-Solana, Shuryak and Teaney, hep-ph/0411315 Stocker, NP A750, 121 Ruppert and Muller, PL B618, 123 Df1 TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

17. pTtrig=3-4, pTassoc=1-2 GeV/c 2-particle corr, bg, v2 subtracted near d+Au min-bias Dφ2=φ2-φtrig Medium away Conical flow Au+Au 10% near Dφ2=φ2-φtrig dN2/dΔφ1dΔφ2/Ntrig Medium away Deflected jets Dφ1=φ1-φtrig Three-particle correlations in d+Au and Au+Au Difference in Au+Au average signal per radian2: center – corner = 0.3 ± 0.3 (stat) ± 0.4 (syst) center – cone = 2.6 ± 0.3 (stat) ± 0.8 (syst) Elongated along diagonal: kT effect? deflected jets? Distinctive features of conical flow are not seen in present data with these pT windows. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

18. Charm in Au+Au • Important test of radiative picture: reduction in energy loss from heavy quark mass • Non-photonic electrons dominantly from charm decay • Suppression in Au+Au relative to d+Au TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

19. STAR V2 Charm and n.p. electron RAA and v2 • Identified D0 consistent with binary scaling at low pT • Non-photonic electrons arise primarily from c and b • Large charm suppression and flow at intermediate pT TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

20. STAR What happens at higher pT? Heavy quarks Light quarks • RdAu consistent with binary scaling • RAA for central Au+Au shows n.p. electrons are very strongly suppressed at high pT • High-pT electron suppression is comparable to incl. charged hadron suppression TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

21. (Maybe) not what we expected! Djordjevic et al, nucl-th/0507019 Armesto et al, private comm. See also Armesto et al, Phys. Rev. D71 (2005) 054027 • b  e should be there, too. Theory: RAA > 0.4 • Data: RAA < 0.3 • Is our understanding of c and b production correct? • Is our understanding of partonic energy loss correct? • How strong are the in-medium interactions? • How dense is the medium? TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

22. System-Size Dependence ! Factor ~3 suppression in central events Suppression roughly at The same level as in NA50 PbPb even though s is 10 times higher ! (?) Data show the same trends within errors for all species and even 62 GeV TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

23. Muon arm Comparison to Theory Muon arm Central arm Theory Vogt: nucl-th/0507027 Model of cold nuclear matter effects in agreement with dAu: Tendency to underpredict suppression in most central AuAu and CuCu events TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

24. System-Size Dependence Models that were successful in describing SPS data (color screeing, co-movers) fail to describe data at RHIC - too much suppression - TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

25. System-Size Dependence Implementing regeneration: much better agreement with the data TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

26. J/y Rapidity Dependence Recombination expects narrowing of rapidity distribution which is not observed TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

27. ! • PHENIX J/y centrality dependence: • Models with only cold nuclear matter effects • don’t have enough suppression • 2) Models with color screening or comovers and • without recombination have too much suppression • 3) Models with recombination are in reasonable • agreement with the data Summarizing this part… • Suppression for most central collisions is similar to NA50 • Energy density and gluon density at RHIC should be much higher • (2-3 times) !? • At RHIC: Recombination compensates stronger QGP screening? TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

28. Some observations • Everything (!!!) flows (, K, K*, p, , d, , , Ω, D) • The flow (v2) seems to be built up very quickly (self quenching effect; seen for particles which may decouple early, seen for particles which contain heavy quarks not “born” flowing) • Preponderance of the evidence begs an explanation in which • Flow is developed when the degrees of freedom are those of quarks and gluons • The initial state (and the transition from it) “facilitate” extremely rapid thermalization • The apparent scaling of the v2 for mesons and baryons with the NCQ suggests the relevant degrees of freedom when the flow is built up is not those of hadrons (BTW, these data are about as good as they will get; the ball is in theory’s court) TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

29. solid: STAR open: PHENIX PRL91(03) Constituent quark scaling - v2 appears to scale with number of constituent quarks. - quark coalescence. NCQ scaling Constituent quark DOF. Deconfinement? “Hydro –like” TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

30. Other things we have learned –We know that the matter is extremely dense and it thermalizes very rapidly. First order estimates of the energy density from dET/d (a la Bjorken), Hydro, and jet suppression results are consistent and all well in excess of the density needed for a QGP predicted by LQCD (~ 10-15 GeV/fm3). – The yields of different hadron species up to and including multi-strange hadrons is consistent with a Grand Canonical Statistical distribution which implies a lower limit on the temperature at chemical freezeout of 160 ± 10 MeV if thermal equilibrium is reached • There is indirect evidence that: • the matter is deconfined • the primary degree of freedom of the matter is that of quarks and gluons • the matter is at high temperature (T > 170 MeV) • Systematic m-dependence of v2(pT) suggests common transverse vel. Field • mT spectra and v2 systematics for mid-central collisions at low pT are well (~20-30% level) described by hydro expansion of ideal relativistic fluid • Hydro success suggests early thermalization, very short mean free path and high initial energy density (e > 10 GeV/fm3) • Best agreement with v2 and spectra for therm < 1 fm/c and soft (mixed-phase- dominated) EOS ~ consistent with LQCD expectations for QGP  hadron • We need a better understanding of the real sensitivity of Hydro predictions to the EOS, and the freezeout treatment, and to improve consistency in describing spectra, v2, and HBT. At present we can not draw quantitative conclusions on the properties of the matter such as the equation of state and the presence of a mixed phase. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

31. Additional thoughts.. The data appear to demand an explanation beyond a purely hadronic scenario: • The lower limit of the energy densities derived fromdET/dhare ~ 4-5 GeV/fm3: The hydro-models require early thermalization(ttherm< 1fm/c)and high initial energy densitye > 10 GeV/fm3 . Their success implies the matter is well described as ideal relativistic fluid • Initial gluon density dng/dy~1000 and initial energy densitye~15 GeV/fm3 are obtained from GLV model of jet quenching. A similarly high initial energy density is obtained by other models. All these estimates of energy density are well in excess of ~1 GeV/fm3 obtained in lattice QCD as the energy density needed to form a deconfined phase. The new results on inclusive suppression to ~ 20 GeV/c and di-jet tomography should allow lower and upper bounds on the gluon density → lower limit on the degrees of freedom TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

32. Conclusion • A qualitatively new form of matter is produced in central • relativistic nucleus-nucleus collisions! • Needed:Further work ongoing to establish this is the quark-gluon plasma • according to our definition. • likely sources of insight on experimental side (in the near term): • soft sector: • open charm elliptic flow (inclusive non-photonic electrons)  • v2 systematics (more particles, better statistics)  • low mass di-leptons  • low pT direct photons  • Fluctuations & multi-particle correlations  • jets and hard probes: • higher pt; search for away side punch-through  • better stats di-hadron correlations wrt reaction plane/ trigger particle  • heavy quark suppression (energy loss) (inclusive n-phot electrons)  • search for forward mono-jets (Run VII) • study of suppression (?) for onium (screening in the plasma)  • theory:provide quantitative assessments of sensitivity (e.g. to EOS) & theoretical  • uncertainties; incorporate higher level effects (e.g. correlations into coalescence) TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

33. Backup Slides TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

34.     Extracting Near-Side Jet Yields d+Au, 40-100% • In Au+Au, jetlike correlation sits on top of an additional, ~flat correlation in  • : cannot differentiate between the two correlations •  : additional correlation gets grouped into subtracted background STAR preliminary Au+Au, 0-5% 3 < pT(trig) < 6 GeV2 < pT(assoc) < pT(trig) TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH:

35. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: