10 12 Degrees in the Shade: Physics of the quark-gluon plasma

1. 1012 Degrees in the Shade:Physics of the quark-gluon plasma Craig Ogilvie • Motivation: non-perturbative quantum chromodynamics (QCD) • Results from RHIC • Properties of quark-gluon plasma to study QCD • Outstanding questions, next steps

2. Perturbation series in as PDG, W.-M. Yao et al., Journal of Physics G 33, 1 (2006) Non-perturbative QCD Strength of QCD interaction determined by the coupling (as) between quarks (q) and gluons (g) g q As as nears 1, perturbative tools fail, what happens to the physics when the interaction is very strong? What new phenomena occur? Craig Ogilvie

3. Strongly interacting system • With large average number q and g • Easier to use to study QCD? • Statistical tools • reduced role of vacuum Two systems to study non-perturbative QCD proton QGP Hive of activity, fluctuations of q-q pairs, g John Lajoie confined by vacuum condensate correlated <qq> Craig Ogilvie

4. Views of heavy-ion collision: Au+Au Thermal freeze-out Hadronization Equilibration Craig Ogilvie

5. Assertion • In these complicated events, we have (a posteriori ) control over the event geometry: • Degree of overlap • Orientation with respect to overlap Central Peripheral Reaction Plane Craig Ogilvie

6. Transverse Dynamics p pT q Craig Ogilvie

7. Physics of the QGP Is plasma locally thermalized? Craig Ogilvie

8. Chemical Equilibrium • Abundance of hadrons determined by their mass and a single common temperature (+ a chemical potential) Yield ~ e-(m/kT) Spectacular agreement over 3 orders => Consistent with system at chemical equilibrium STAR Preliminary Craig Ogilvie

9. Exponential Spectra: • Random motion + collective expansion (b=v/c ~ 0.6) • Heavier particles larger increase in pt due to expansion • Expanding, thermal system Craig Ogilvie

10. Expansion is not isotropic coordinate-space-anisotropy  momentum-space-anisotropy • If thermalized => pressure gradient is largest in x-direction • Expansion larger in that direction • Anisotropy characterized by elliptic flow, v2 y py px x dn/df ~ 1 + 2v2(pT) cos (2 f) + ... Craig Ogilvie

11. 2v2 Expansion is hydrodynamic • Initial asymmetry propagates to final state • Low momentum particles reproduced by hydro ( 99% of the particles) • System thermalizes early (Dt < 0.6 fm/c) Craig Ogilvie

12. What is flowing? • Quark scaling: divide by nq valence quarks in particle • Convert to energy axis (system does work) Universal scaling => system flows while it is deconfined quarks Craig Ogilvie

13. Physics of the QGP Does the QGP behave like a gas of quarks/gluons, or? Plasma appears to be locally thermalized Ongoing question: temperature via emission of photons Craig Ogilvie

14. Current :) predicted QCD phase diagram Marzia Rosati, LHC T (MeV) Hot QGP Attractive interactions in plasma Non-perturbatively strong as(q) large, since momentum transfer ~ T Correlated qq sQGP 200 packed hadrons nuclei m (MeV) Craig Ogilvie

15. u1 Exchange of constituents Long mean-free path Eff. Transport of p Strong coupling between fluid elements increases h Z Donko, Phys Plasma 7, 45 (2000) Probe of strongly coupled fluid: shear viscosity u1 2 • Shear gradient of velocity distribution du1/dx2 • Viscosity h reduces shear gradients, e.g. by transport of constituents from one fluid-cell to another 1 Minimum viscosity coupling Craig Ogilvie cQGP, Nucl-th/0601029

16. P. Romatschke, nucl-th:0706.1522 Shear viscosity reduces elliptic flow Quantum lower bound? Perturbative QCD h/s >0.5 => sQGP Calc h/s in non-perturbative QCD… RHIC viscosity close to conjectured lower quantum bound perfect fluid? Craig Ogilvie

17. Viscosity in other systems Kovtun et al, PRL 94 111601 (2005) Physics Today, 58(5) • Perfect fluid has h=0 (or lower bound h/s > 1/4p) RHIC, 4p*h/s~ 1 at 1012 K Craig Ogilvie

18. Physics of the QGP QGP behaves like a strongly coupled liquid, h key Ongoing question: Charm-quark binding with di-quark => flow, spectra, Lc Plasma appears to be locally thermalized How dense is the QGP? Craig Ogilvie

19. Hard Scattered Parton {Quark or Gluon} hard-scattered parton: high pt-transfer, calc. with perturbative QCD hard-scattered parton during Au+Au hadrons have less energy, broader angular spread ? cone of hadrons, pt leading hadron parton loses energy within plasma high pt p p Craig Ogilvie

20. Baseline p+p p0 spectra compared to pQCD • parton distribution functions, for partons a and b • measured in DIS, universality • perturbative cross-section (NLO) • requires hard scale • factorization between pdf and cross section • fragmentation function • measured in e+e- Phys. Rev. Lett. 91, 241803 (2003) Craig Ogilvie

21. High-pt parton loses energy within QGP • High-pt parton scatters in plasma, radiates gluons • Radiated gluon has formation time ~ 1/Egluon • During formation time, scatter from many partons in plasma • Multiple-scatters treated coherently • Reduces total gluon emission rate • Reduces energy-loss (though still large :) L Scattering centers = color charges q q g Craig Ogilvie

22. RAA = ratio (Au+Au)/(p+p) Au+Au p0 spectra Enhanced Suppressed Craig Ogilvie

23. L q q g How Opaque is QGP? Scattering power of the QCD medium: Range probable values Craig Ogilvie

24. QGP R. Baier Pion gas Cold nuclear matter Strong energy-loss not fully understood RHIC data Larger than expected from QGP that interacts perturbatively Calculate q in non-perturbative QCD, compare to expt Craig Ogilvie

25. parton loses energy within plasma Fate of Gluons • Jets broader in Cu+Cu than p+p • Fragmentation of induced gluon radiation? Do radiated gluons produce broader jet? Nathan Grau, Hua Pei Craig Ogilvie

26. Physics of the QGP QGP behaves like a strongly coupled liquid Plasma appears to be locally thermalized QGP is opaque colored system, Scattering power, q, is key Ongoing question: is the modeling of gluon radiation right? Energy-loss of charm-quarks Craig Ogilvie

27. e X De+X Au Au B e+X e X VTX $8M upgrade, C. Ogilvie project manager Designed to provide early time probe Charm, beauty: open questions sQGP silicon pixel+strip detectors Tracks extrapolate back to collision Displaced vertices => charm (D), beauty (B) Requires ~ 50 mm precision Craig Ogilvie

28. VTX VTX Craig Ogilvie

29. Wafers Testing at BNL Rachid Nouicer (BNL), Kieran Boyle (SBU), Hua Pei (ISU) and Junkichi Asai (RBRC) BNL RBRC ISU SBU Craig Ogilvie

30. Strip Front-End Electronics On the ladder Signal from hit strip => digitized => collected by read-out-card (ROC) • Led by Alan Dion (ISU post-doc) • Testing, debugging ROCs • Optimizing ROC+sensor Craig Ogilvie

31. eRHIC To establish the existence, then study the strongest possible gluon field • Process continues until saturation • Maximum strength color field Kirill Tuchin Gluon splitting => lower momenta Craig Ogilvie

32. Summary Non-perturbative QCD As as nears 1, perturbative tools fail, what happens to the physics when the interaction is very strong? • Strongly coupled QGP • Colored, opaque, and low-viscosity • Use these quantities (q, h) to test QCD Open questions <= VTX upgrade • Energy-loss + gluon radiation • Charm coupled to di-quarks in fluid? Craig Ogilvie

33. Thanks! Craig Ogilvie

34. Backup Craig Ogilvie

35. Viscosity lower bound For dilute systems, h ~ mean free path, transport of momentum across fluid cells For relativistic systems, number of particles not so well defined, Entropy density s ~ kBn Craig Ogilvie

36. spectra (p) HBT b Expansion Craig Ogilvie

37. PHENIX Experiment at RHIC • In operation since 2000 • Designed for penetrating probes to characterize QGP Focus on mid-rapidity arms Charged tracking + Calorimetry => photons, p0…+ J/y,… Craig Ogilvie

38. √s=200 GeV, p+p => x NLO QCD agrees well with data D. d’Enterria nucl-ex/0611012 Craig Ogilvie

39. Partons lose energy as they travel through QGP p0 spectra at √s=200 GeV nucl-ex/0611007 PHENIX • p+p cross-section scaled by parton-flux in Au+Au • Fewer high-pt p0 in Au+Au • Energy-lost by parton => info on density of QGP Eloss Craig Ogilvie

40. Ratio of (Au+Au)/(scaled p+p spectra) • Mesons suppressed  5 → energy-lost in QGP • g scale with parton flux Drop possibly due to isospin difference p+p and A+A Craig Ogilvie

41. Particles correlated with high-pt trigger STAR Df = f1-f2 • Correlation survives high-multiplicity environment of A+A p+p, PHENIX PRD, 74 072202 (06). A+A Craig Ogilvie

42. 3 < pt,trigger < 4 GeV pt,assoc. > 2 GeV Au+Au 0-10% preliminary Response of medium to passage of high-pt parton • Near-side, generation of ridge => strength large Dh (STAR talk) • Far-side: does super-sonic parton generate a mach-cone ? hep-ph/0410067; H.Stocker… Jorge Casalderry-Solana Craig Ogilvie

43. centrality Far-side Production of Particles PHENIX preliminary nucl-ex/0611019 1<pt,ass<2.5<pt,trig<4 GeV/c Observation of particles produced ~1 radian away from back-to-back! Fit with 2 Gaussians, each D radians away from p D scales with system size =>emission consistent with medium’s response to jet Craig Ogilvie

44. Suppression of heavy-quark spectra in A+A PHENIX nucl-ex/0611018 PRL in press Suppression of e, pT>3.0 GeV/c Slightly smaller than light quarks Challenge for models to reproduce both light, heavy-q Eloss Expt. need to increase statistics, reduce systematics silicon upgrade=> displaced vertices Craig Ogilvie

45. Spectra: • Random motion + collective expansion (b=v/c) • Heavier particles are boosted more by expansion • Expanding, thermal system Craig Ogilvie