T. Hallman ICHEP06 Moscow July 31, 2006

1. New Results and Future Perspectives in Relativistic Heavy Ion Physics T. Hallman ICHEP06 Moscow July 31, 2006

2. Outline of this talk • Recent results from RHIC & SPS • Hard Probes(RAA ofheavy quarks, di-hadron correlations) • Quarkonium • Interplay of high pT partons with the medium • Flow, global observables, etc. • Search for QCD Critical point • On the eve of new discoveries at the LHC • Summary

3. N. Armesto: ICHEP06 Jet quenching/heating Quarkonium suppression Control of the benchmark: prompt photons and dileptons 1. Introduction: • Hard processes (probes of the medium created in a HIC): those whose benchmark (result of the probe in cold nuclear matter) is computable within perturbative QCD, for which a hard scale is required (pT, mQ,...>>1/Rh). • Strategy: no medium (pp) and cold nuclear matter (pA) understood in pQCD define the benchmark for the probe; results in hot medium (AB) and their difference with expectation provide a (pQCD or not) characterization. 3 Hard Processes in Heavy Ion Collisions

4. Inclusive jets p0 pQCD in p+p at RHIC Good agreement with NLO pQCD  pQCD should be broadly applicable at RHIC (e.g. heavy flavor production…)

5. p+p Binary collision scaling By comparison, in central Au+Au collisions, jet quenching is observed: hadrons are suppressed; direct photons (the control) are not as we expect Nuclear Modification Factor sNN = 200

6. Q Up to QM05, a reasonably strong consensus that the suppression was basically understood: radiative energy loss in a medium 30-50 times normal nuclear matter density Then these measurements were extended to the heavy quark sector (c, b) by studying suppression of electrons from their semi-leptonic decays Heavy quark energy loss Dokshitzer, Khoze, Troyan, JPG 17 (1991) 1602. Dokshitzer and Kharzeev, PLB 519 (2001) 199. • In vacuum, gluon radiation suppressed at q < mQ/EQ • “dead cone” effect: heavy quarks fragment hard into heavy mesons Dead cone also implies lower heavy quark energy loss in matter: (Dokshitzer-Kharzeev, 2001)

7. S.Wicks et al., nucl-th/0512076 Armesto et al., Phys.Lett.B637:362-366,2006 Heavy flavor suppression via b,c  e+X RAA(non-photonic electrons) ~ 0.2 ~RAA(p0) !! • Gluon density/qhat constrained by light quark supression+entropy density (multiplicity) •  under-predicts electron suppression •  charm vs beauty? elastic energy loss? …?

8. S.Wicks et al., nucl-th/0512076 Elastic (collisional) energy loss revisited • Elastic DE comparable to Radiative DE – not negligible • Elastic DE important even for light quarks •  revisit energy density estimates?

9. One possibility: maybe all the non-photonic electrons are from charm decays? Submitted to PRL, nucl-ex/0607012 BDMPS: N. Armesto et al, nucl-ex/0511257 DGLV: Wicks et al, nucl-ex/0512076 c+b, radiative only c+b, collisional+radiative c only, collisional+radiative

10. D0 ~factor 2 CDF, PRL 91, 241804 (2003) M. Cacciari, Hard Probes STAR, nucl-ex/0607012 FONLL Another thing to understand: N. P. electrons in p+p at RHIC vs FONLL State of the art: Fixed-Order Next-to-Leading Log ? Tevatron charm and beauty vs FONLL: OK • RHIC n.p. electrons: factor 3-5 excess(!) • Large ambiguity in relative contribution of • ce/be •  need to resolve b and c explicitly NB: Consistent data between multiple independent measurements; problem is comparison with theory

11. The short summary: • Resolution of non-photonic electron suppression puzzle needs • experiment: explicit measurement of c vs b suppression • theory: unified framework incorporating both elastic and radiative • energy loss

12. trigger ? 4< pTtrig < 6 GeV pTassoc > 2 GeV pTassoc > 0.15 GeV recoil cos(Df) STAR, Phys Rev Lett 91, 072304 STAR, Phys Rev Lett 95, 152301 Di-hadron correlations: recoiling jets are strongly modified due quenching Well established experimental observation

13. trigger Yield per trigger pTtrigger>8 GeV/c ? recoil STAR, nucl-ex/0604018 What is new: di-hadron correlations at higher pT Armesto: ICHEP06 Recoil jet clearly seen above background but at suppressed rate

14. D(zT) Recoiling hadron distribution p Df Recoiling hadrons: details No modification of fragmentation No angular broadening STAR, nucl-ex/0604018 Recoil rate is suppressed but jet features unmodified  see only non-interacting jets? Detailed dynamical calculations (see T. Renk, hep-ph/0602045) suggest  75% of observed recoils are due to non-interacting jets c.f. Armesto: ICHEP06

15. High PT Summary • Experiment • jet quenching is well-established: multiple strong effects • key open issue: how does the medium respond to DE? • second generation of high precision measurements: • heavy flavor, correlations, g+jet • RHIC upgrades (topological charm reco), high luminosity (g+jet) • LHC brings qualitatively new physics • Theory • qualitative but not yet quantitative understanding of jet quenching • significant uncertainties in • underlying mechanism (elastic vs radiative) • heavy quark production • modeling of dynamical evolution

16. N. Armesto: ICHEP06 Conclusions: • Hard processes in HIC have a twofold interest: * Extension of pQCD to new domains: new theoretical tools, relation with other domains (hard QCD, high density QCD),... * Characterization of the produced medium. • Together with v2 and the (anti)baryon to meson anomaly, they have been key to establish the production of high density matter in HIC at RHIC. • Lesson from RHIC:control experiments (pp, dAu) must be an integral part of the HIC program to get clear conclusions. • LHC: large yields of hard processes will be available: if problems are solved, this subject will play a central role in the heavy ion program. 16 Hard Processes in Heavy Ion Collisions

17. Quarkonia

18. Projectile J/y L Target NA38/NA50 J/yproduction from p-A to Pb-Pb collisions The study of J/y production in p-A collisions at 200, 400 and 450 GeV, by NA3, NA38, NA50 and NA51, gives a “J/y absorption cross-section in normal nuclear matter” of 4.18 ± 0.35 mb. 450 GeV 400 GeV 200 GeV extrap. to 158 GeV J/y normal nuclear absorption curve S(J/y) ~ exp(-r L sabs) In S-U and peripheral Pb-Pb collisions, the data points follow this normal nuclear absorption, which scales with L, the length of nuclear matter crossed by the (pre-resonant) J/y. In central Pb-Pb collisions the L scaling is broken and an “anomalous suppression” sets in. Woehri: ICHEP06

19. J/y / DY analysis Set A (lower ACM current) Set B (higher ACM current) • Combinatorial background (, K decays) from event mixing method (negligible) • Mass shape of signal processes from MC (PYTHIA+GRV94LO pdf) • Multi-step fit: a) DY (M>4.2 GeV), b) IMR (2.2<M<2.5 GeV), c) charmonia (2.9<M<4.2 GeV) • Results from set A and B statistically compatible → use their average in the following • Stability of the J/y / DY ratio: • change of input distributions in MC calculation → 0.3% (cosq), 1% (rapidity) • level of muon spectrometer target cut → < 3% Woehri: ICHEP06

20. Anomalous suppressionpresent in Indium-Indium • Qualitative agreement with NA50 results plotted as a function of Npart • Data points have been normalised to the expected J/y normal nuclear absorption, calculated with • as measured with p-A NA50 data • B. Alessandro et al., Eur. Phys. J. C39(2005) 335 J/abs = 4.18  0.35 mb J/y / DY vs. centrality bin1  Npart = 63 bin2  Npart = 123 bin3  Npart = 175 3 centrality bins Woehri: ICHEP06

21. Comparison with other SPS results The J/y suppression patterns are in fair agreement when plotted versus Npart Woehri: ICHEP06

22. Comparison with the extreme case of a step-like function Meas/Exp 1 A1 A2 Npart Step position Step position: Npart = 82 ± 9 A1= 0.98 ± 0.03 A2= 0.85 ± 0.01 2/dof = 2.0 Resolution on Npart estimate (due to the measured EZDC resolution) taken into account A certain amount of physics smearing can be accommodated by the data Woehri: ICHEP06

23. N. Armesto, ICHEP06 Sequential suppression: • In the last 5 years, lattice results and potential model calculations support a sequential melting of quarkonium in the QGP. • Sequential melting provides an alternative mechanism (others: comovers, percolation,...) to explain data (Karsch, Kharzeev, Satz '05): pT broadening? 23

24. RHIC Baseline Measurements Deuteron-Gold at 200 GeV Consistent with 1-3 mb nuclear absorption and modest hint of shadowing effect Proton-Proton at 200 GeV s(ppJ/) = 2.610.200.26mb PHENIX PRL96 (2006) 012304

25. Preliminary RHIC Gold-Gold Results Higher energy density at RHIC leads to prediction of greater suppression than at SPS. Suppression Factor Arkhipkin, Armesto: ICHEP06 Collision Centrality Models over predict suppression. In fact, suppression is very similar to that found at the SPS (?): charm recombination, no J/y melting, only cc? CuCu, AuAu J/y data as a function of centrality, rapidity and pT will hopefully settle these questions.

26. Interplay of high pT partons with the medium: one of the most exciting questions

27. 3<pt,trigger<4 GeV pt,assoc.>2 GeV Au+Au 0-10% preliminary Armesto et al, nucl-ex/0405301 Medium response to jet energy loss ? One example: near-side “ridge” correlated with jet trigger Dh Df Induced radiation dragged by longitudinally expanding fluid?

28. Another intriguing conjecture Three-particle correlations which would show such effects (mach cone, Cherenkov gluons) are actively being pursued by STAR and PHENIX

29. Flow, Global Observables, etc.

30. RHIC Initial Conditions: CGC 19.6 GeV 130 GeV 200 GeV Charged hadron pseudo-rapidity  PHOBOS Collaboration 1) High number of Nch indicates initial high density; 2) Mid-y, Nch Npart nuclear collisions are not incoherent; 3) Saturation model works (Kharzeev et al) Initial high parton density at RHIC PRL 85, 3100 (00); 91, 052303 (03); 88, 22302(02); 91, 052303 (03) Xu: ICHEP06

31. data Thermal model fits Tch = 163 ± 4 MeV B = 24 ± 4 MeV Yield Ratio Results pT-integrated particle yield ratios in central Au+Au collisions consistent with Grand Canonical Stat. distribution across u, d and s quark sectors (S= 1). Inferred Temp. consistent with Tcrit (LQCD)  phase transition • The system is thermalized at RHIC. • Short-lived resonances show deviations. There is life after chemical freeze-out. RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184. Xu: ICHEP06

32. z y x Anisotropic Flow py px Elliptic Flow in Heavy Ion Collisions Peripheral Collisions

33. Comparison of elliptic flow and predictions of hydro potentially provide evidence for local thermalization and an EOS with a soft point P. Huovinen, private communications, 2004 • Minimum bias data! At low pT, model result fits mass hierarchy well! • - Details do not work, need more flow in the model! Xu: ICHEP06

34. STAR Preliminary  -mesons Flow: Partonic Flow • -mesons are very special: • they do not re-interact in hadronic environment • they show strong collective flow • they are formed via coalescence with thermal s-quarks • STAR Preliminary: QM05, M. Lemont, S. Blyth • Hwa and Yang, nucl-th/0602024; Chen et al., PRC73 (2006) 044903 Xu: ICHEP06

35. Collectivity, Deconfinement at RHIC - v2 of light hadrons and multi-strange hadrons - scaling by the number of constituent quarks At RHIC:  mT - NQ scaling  Partonic Collectivity  Deconfinement PHENIX: PRL91, 182301(03) STAR: PRL92, 052302(04), 95, 122301(05) nucl-ex/0405022, QM05 S. Voloshin, NPA715, 379(03) Models: Greco et al, PRC68, 034904(03) Chen, Ko, nucl-th/0602025 Nonaka et al. PLB583, 73(04) X. Dong, et al., Phys. Lett. B597, 328(04). …. i ii Xu: ICHEP06

36. KET/n scaling across collision centralities R. Lacey KET/n scaling observed across centralities Lacey: ICHEP06

37. A remarkable scaling of the fine structure of elliptic flow is observed at RHIC At midrapidity v2 (pt,M,b,A)/n = F(KET/n)*ε(b,A) R. Lacey Lacey: ICHEP06

38. v2{2}, v2{4}, non-flow, and flow fluctuations Non-flow Flow fluctuations • Several reasons for v to fluctuate in a centrality bin: • Variation in impact parameter in a centrality bin (taken out in STAR results) • Real flow fluctuations (due to fluctuations in the initial conditions or in the system evolution) • Non-flow (not related to the orientation • of the reaction plane) correlations: • resonance decays • inter and intra jet corelations 2 equations, at least 3 unknowns: v, δ, σ Subject of this talk • Different directions to resolve the problem: • - Find methods which suppress / eliminates non-flow • Add more equations assuming no new unknowns • Estimate flow fluctuations by other means Correlations with large rapidity gaps Use equations for v2{n}, n>4 Voloshin: ICHEP06

39. v2 from (Forward TPC * Main TPC) correlations Shown in black are resultsobtained by correlatingtwo random particles from Main TPC. Non-flow contribution can be largeand positive. In blue are results forv2in the Main TPC regionobtained from correlations (Forward*Main) and (East*West). These resultsare affected insignificantly by non-flow correlations. Note: significantly largerrelative non-flow contribution in Cu+Cu case compared to Au+Au | η| < 0.9 (Main TPC) -3.9 < η < -2.9 (FTPC East) 2.9 < η< 3.9 (FTPC West) Voloshin: ICHEP06

40. Some next steps for flow studies Disentangle fluctuations and correlations to measure <v2> and use the rapidity dependence of the v2 fluctuations to eliminate the uncertainty in the initial conditions (CGC or Glauber) Understand non-flow at high pt to extract precise particle type dependence of intermediate and high pt v2 Study the systematics (pt, centrality and -/sNN dependence) of ncq scaling and phi or Omega v2. Do indications of a quark and gluon phase disappear anywhere? Measure direct D meson v2

41. Energy Dependence of Particle Production PHOBOS PRL 91,52303 (2003) PHENIX @ QM01 Nucl. Phys. A698, 171 (2002). dNch/dη ~ ln(√s) PHENIX PRC 71, 034908 (2005) dNch/dη = (½Npart·A)ln(√sNN/√s0) A = 0.74±0.01 √s0 = 1.48±0.02 GeV LHC prediction based on data trend for 350 participants: dNch/dη @ η=0: 1100 Total Nch : 13000 Milov: ICHEP06

42. Ejiri, et.al. Taylor Expansion Fodor, Katz Lattice Re-weighting The QCD critical point search Gavai, Gupta B Lower Limit B √sNN ——————————————————— 180 MeV 25 GeV 420 MeV 7.5 GeV 725 MeV 4.5 GeV ——————————————————— Cleymans, et.al. M. Stephanov: hep-ph/0402115 For B=0, lattice QCD predicts asmooth crossover between hadrons and quark-gluon plasma at Tc=190 MeV For B>0, lattice calculations are less reliable: predictions for location of the critical point are highly uncertain

43. NUCLOTRON JINR Project parameters:maximum energy 5 GeV/nucl.fornuclei with А ~ 200. Upgraded Nuclotron: up to 10 GeV/nucl. Sissakian, Sorin, Toneev: ICHEP06

44. Conclusions • A study of the phase diagram in the domain populated by heavy-ion • collisions with the bombarding energy ~ 5 ÷10GeV/nucleontosearch for the mixed phase seems to be avery attractive task. • 2. The use of the isospin asymmetry as anadditional conserving parameter to characterize the created hotand dense system attracts new interest in this problem (critical end-boundary hypersurface ? ). • 3. The available theoretical predictions are stronglymodel dependent giving ratherdispersive results. There are nolattice QCD predictions for this highly nonpertubative region. Much theoretical work should be done and only future experimentsmaydisentangle these models. • A JINR Nuclotron possibility of accelerating heavy ions to theproject energy of 5A GeV and increasing it up to 10A GeV can berealized in two-three years. This will enable us to effort aunique opportunity for scanning heavy-ion interactions in energy,centrality and isospin asymmetry. It seems to beoptimal to have the gold and uranium beams in order to scan inisospin asymmetry in both central and semi-central collisions atnot so high temperatures. Sissakian, Sorin Toneev: ICHEP06

45. Large Heavy-ion Collider (LHC)

46. Solenoid magnet 0.5 T Cosmic-ray trigger HMPID • Forward detectors • FMD, T0, V0, ZDC • PMD Dipole Magnet Tracking Stations PHOS • Central tracking system • ITS • TPC • TRD • TOF • absorbers • trigger chambers Muon Spectrometer The ALICE Detector Safarik: ICHEP06

47. ALICE PID • p, K, p identified in large acceptance (2p * 1.8 units h) via a combination of dE/dx in Si and TPC and TOF from ~100 MeV to 2 (p/K) - 3.5 (K/p) GeV/c • Electrons identified from 100 MeV/c to 100 GeV/c (with varying efficiency) combining Si+TPC+TOF with a dedicated TRD • In small acceptance HMPID extends PID to ~5 GeV • Photons measured with high resolution in PHOS, counting in PMD, and in EMC Alice uses ~all known techniques! p/K TPC + ITS (dE/dx) K/p e /p p/K TOF e /p K/p HMPID (RICH) p/K K/p 0 1 2 3 4 5 p (GeV/c) TRD e /p PHOS g /p0 1 10 100 p (GeV/c) Safarik: ICHEP06

48. Hadroniccharm Combine ALICE tracking + secondary vertex finding capabilities (sd0~60mm@1GeV/c pT) + large acceptance PID to detect processes asD0K-+ ~1 in acceptance / central event ~0.001/central event accepted after reconstruction and all cuts Results for 107 PbPb ev. (~ 1/2 a run) significance vs pT S/B+S ~ 37 S/B+S ~ 8 for 1<pT<2 GeV/c (~12 if K ID required) Safarik: ICHEP06

49. Charm in pp (D0→ Kp) Sensitivity to NLO pQCD params s = 14 TeV down to pt ~ 0 ! Safarik: ICHEP06

50. 0 1 2 10 100 pt (GeV/c) LHC Experiments Qs T=LQCD Single particle spectra Correlation studies Jet reconstruction Hard processes Modified by the medium Bulk properties ALICE PID CMS&ATLAS Safarik: ICHEP06