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

2. 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

3. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 3 Definition of the terms QGP, v 2, and R AA (R CP ) 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  1 st - or 2 nd -order phase transition  evidence of chiral symmetry restoration

4. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 4 Anisotropic Flow x y z pxpx pypy V 2 (Elliptic Flow) Peripheral Collisions Hydro calculations: Kolb, Heinz and Huovinen Comparison with hydro suggests early (local) thermalization of the matter and an EOS with a soft point

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

6. 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.): Linear dependence on gluon density  glue : measure  E  gluon density at early hot, dense phase High gluon density requires deconfined matter (“indirect” QGP signature !) Gluon bremsstrahlung Thin plasma (Gyulassy et al.):

7. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 7 An old story by now… Phys. Rev. Lett. 91, 072304 (2003). Pedestal&flow subtracted STAR 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

8. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 8 What’s New for the Inclusives? Significantly higher P T System Size Systematics Partonic (vs hadronic) energy loss Matter is surprisingly opaque Should provide lower bound on dN g /dy R AA for CuCu: same behavior for the same N part as in AuAu, but better precision

9. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 9 Inclusive Suppression: R AA in Cu+Cu 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 √ s NN =200 GeV

10. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 10 Geometrical Dependence of R AA R AA scales smoothly from Au+Au through Cu+Cu to p+ Scaling prefers N part 1/3, though N part 2/3 not strongly excluded p+p

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

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

13. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 13 Di-jets and the interaction mechanism ~0.54 ~0.25 Scaling factors relative to d+Au 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? 8 < p T (trig) < 15 GeV/c

14. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 14 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] X-N Wang, PLB 595, 165 (2004) = STAR preliminary 8 < p T (trig) < 15 GeV/c

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

16. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 16 Conical flow? Medium away near Deflected jets  1  2  1  2 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 Casalderrey-Solana, Shuryak and Teaney, hep-ph/0411315 Stocker, NP A750, 121 Ruppert and Muller, PL B618, 123 away near Medium Conical flow

17. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 17 p T trig =3-4, p T assoc =1-2 GeV/c 2-particle corr, bg, v2 subtracted  φ 2 = φ 2 - φ trig d+Au min-bias dN 2 /d Δφ 1 d Δφ 2 /N trig  φ 1 = φ 1 - φ trig  φ 2 = φ 2 - φ trig Au+Au 10% Three-particle correlations in d+Au and Au+Au Elongated along diagonal: k T effect? deflected jets? Distinctive features of conical flow are not seen in present data with these p T windows. Difference in Au+Au average signal per radian 2 : center – corner = 0.3 ± 0.3 (stat) ± 0.4 (syst) center – cone = 2.6 ± 0.3 (stat) ± 0.8 (syst) Medium away near Deflected jets away near Medium Conical flow

18. 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

19. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 19 Identified D 0 consistent with binary scaling at low p T Non-photonic electrons arise primarily from c and b Large charm suppression and flow at intermediate p T Charm and n.p. electron R AA and v 2 STAR V 2

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

21. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 21 (Maybe) not what we expected! Djordjevic et al, nucl-th/0507019Armesto et al, private comm. b  e should be there, too. Theory: R AA > 0.4 Data: R AA < 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? See also Armesto et al, Phys. Rev. D71 (2005) 054027

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

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

24. 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 -

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

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

27. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 27 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? PHENIX J/  centrality dependence: 1)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

28. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 28 Some observations Everything (!!!) flows ( , K, K*, p, , d, , , Ω, D) The flow (v 2 ) 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 v 2 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)

29. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 29 Constituent quark scaling Constituent quark DOF. Deconfinement? solid: STAR open: PHENIX PRL91(03) - v 2 appears to scale with number of constituent quarks. - quark coalescence. “Hydro –like” NCQ scaling

30. 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 dE T /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/fm 3 ). – 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 v 2 (p T ) suggests common transverse vel. Field –m T spectra and v 2 systematics for mid-central collisions at low p T 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 (  > 10 GeV/fm 3 ) –Best agreement with v 2 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, v 2, 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.

31. 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 from dE T /d  are ~ 4-5 GeV/fm 3 : The hydro-models require early thermalization (  therm 10 GeV/fm 3. Their success implies the matter is well described as ideal relativistic fluid –Initial gluon density dn g /dy ~1000 and initial energy density e~15 GeV/fm 3 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/fm 3 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

32. 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)  v 2 systematics (more particles, better statistics) low mass di-leptons low p T 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)

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

34. TJH: ISMD 2005, 8/9-15 Kromeriz, Czech Republic TJH: 34     Extracting Near-Side Jet Yields 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 d+Au, 40-100% Au+Au, 0-5% STAR preliminary 3 < p T (trig) < 6 GeV 2 < p T (assoc) < p T (trig)

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