Connecting the Lattice Points: What Lattice QCD can tell us about the Quark Gluon Plasma

1. Connecting the Lattice Points:What Lattice QCD can tell us about the Quark Gluon Plasma What Experiment can tell us about the Quark Gluon Plasma Barbara Jacak Stony Brook University July 14, 2011 Many thanks to Ron Soltz!

2. Outline • Experimental study of QCD at high T & density • Context • Some new insights from LHC and RHIC • Properties of the Quark Gluon Plasma • Selection of what we are learning from data • Key role of Lattice QCD • NB: I will not discuss energy loss (much) • QCD Phase diagram • Insights from data + Lattice • Compelling (new) questions • How we’ll study them experimentally • A plea for guidance from lattice

3. Study QCD at high T, r

4. STAR RHIC at Brookhaven to heat matter up Collide Au + Au ions for maximum volume s = 200 GeV/nucleon pair, p+p and d+A to compare

5. The Tools STAR specialty: large acceptance measurement of hadrons PHENIX specialty: rare probes, leptons, and photons

6. LHC collides Pb+Pb at 2.76 TeV per NN

7. Pb+Pb studied by 3 experiments ALICE

8. PRL104, 132301 2010 Temperature reached? thermal radiation e+ Low mass, high pT e+e- nearly real photons Large enhancement above p+p in the thermal region  e-  pQCD spectrum (QCD Compton scattering) agrees with p+p data

9. 9 direct photons: Tinit > Tc ! • Exponential fit in pT: Tavg = 221 ±23 ±18 MeV • Multiple hydrodynamics models reproduce data Tinit ≥ 300 MeV > 4 trillion degrees! Tc~ 170 MeV

10. RHIC puts us here … what do we know about QGP? Now we are on the map Ideal Gas Plasma Energy density / T4 Hadrons Temperature Tc ~ 170 ± 10 MeV  ~ 3 GeV/fm3

11. Example of the viscosity of milk. Liquids with higher viscosities will not make such a splash when poured at the same velocity. QCD matter at T =300-600 MeV (at RHIC) • Collective flow with low viscosity/ • entropy ratio: “perfect liquid” • How low? Strong coupling… • Opacity very high • Effectively stops quarks & gluons • How and why? Strong coupling… • Even heavy quarks lose energy & flow • Not expected from pQCD; mechanism? • -> strong coupling • High mass scatterers • Color is screened • How much? Non photonic electrons 0, 

12. Strong coupling: forefront issue in other fields! Quark gluon plasma is like other systems with strong coupling– all exhibit liquid properties & phase transitions Cold atoms: coldest & hottest matter on earth are alike! Dusty plasmas & warm, dense plasmas have liquid and even crystalline phases Strongly correlated condensed matter: liquid crystal phases and superconductors In all these cases have a competition: Attractive forces  repulsive force or kinetic energy Result: many-body interactions;quasiparticles exist? 

13. Calculating transport in QGP weak coupling limit∞ strong coupling limit perturbative QCD not easy! Try a pure field… kinetic theory, cascades gravity supersym 4-d interaction of particles (AdS/CFT) 23,32,n2…

14. What are the properties of hot QCD matter? • thermodynamic (equilibrium) • T, P, r • Equation Of State (relation btwn T, P, V, energy density) • vsound, static screening length • transport properties (non-equilibrium)* • particle number, energy, momentum, charge • diffusion sound viscosity conductivity In plasma: interactions among charges of multiple particles charge is spread, screened in characteristic (Debye) length,lD also the case for strong, rather than EM force *measuring these is new for nuclear/particle physics! Nature is nasty to us: does a time integral…

15. Experiment and Lattice can explore together: • QGP properties • T, EOS • Viscosity, diffusion • (color) screening • Features of the phase diagram • Tc, critical point location & signatures • Change in signatures with first order • phase transition • Thermal radiation • maybe also pre-equilibrium in the data?

16. Lepton pair emission  EM correlator Medium modification of meson Chiral restoration Hadronic contribution Vector Meson Dominance q qq annihilation Thermal radiation from partonic phase (QGP) q e.g. Rapp, Wambach Adv.Nucl.Phys 25 (2000) Emission rate of dileptons per volume g*ee decay Boltzmann factor temperature EM correlator Medium property From emission rate of dileptons, the medium effect on the EM correlator as well as temperature of the medium can be decoded. Yasuyuki Akiba - PHENIX QM09

17. Calculate the correlator on the lattice • non-perturbative contributions to thermal dilepton rates at low mass • For small energy, w/T<(1-2) spectral function > free form • For ω/T ≃ 1 thermal dilepton rate ~ order of magnitude > leading order Born rate • for ω/T>∼(2 − 4) the spectral function is close to the free form From fit to lattice spectral fn. in Phys.Rev.D.83.034504 (2011)

18. e+e-excess at low mass, low pT Excess at Mee < 2-3 Tc Non-perturb. thermal contribution? And/or pre-equilibrium? PRC81, 034911 (2010)

19. Thermal photons flow! arXiv:1105.4126 Au+Au@200 GeV minimum bias Au+Au@200 GeV minimum bias Au+Au@200 GeV minimum bias Statistical subtraction inclusive photon v2 - decay photon v2 = direct photon v2 p0v2 Direct photon v2 inclusive photon v2 inclusive photon v2 p0v2 similar to inclusive photon v2 Flow magnitude is surprising. Can “extras” explain it?

20. Can we locate the critical point? S. Gupta, QM2011

21. Fluctuations as Critical Point Signature PL B 2010.10046 • Measured baryon fluctuation ratios from STAR are so far consistent with the Hadron Resonance Gas • Calculations of higher moments from LQCD deviate from HRG calculations and may provide conclusive evidence for critical point if observed in data * You are under no obligation to use heavy ion data for scale setting when more precise methods exist

22. Beam Energy Scan at RHIC

23. z y x Almond shape overlap region in coordinate space Measuring collective flow: start with v2 momentum space dN/df ~ 1 + 2 v2(pT) cos (2f) + … “elliptic flow”

24. Kolb, et al Hydrodynamics reproduces elliptic flow of q-q and 3q states Mass dependence requires soft EOS, NOT gas of hadrons Matter flows like a ~ideal liquid • huge pressure buildup • large anisotropy rapid equilibration only works if viscosity/entropy is near the minimum for a quantum system (1/4p) “perfect” liquid (D. Teaney, PRC68, 2003)

25. Elliptic flow scales with quark number transverse KE implication: valence quarks, not hadrons, are relevant DOF coalesce into hadrons when T falls below Tc consistent with success of hydro with lattice EOS, but… what gives? dressed quarks are born of flowing field? Nb: strongly interacting liquids lack well-defined, long-lived quasi-particles

26. STAR at RHIC How does LHC plasma compare with RHIC? ALICE Preliminary, STAR, PHENIX and E895 data ALICE pT = 1.7 GeV pT = 0.7 GeV v2 saturates @ 39 GeV 103 104 @ LHC Tinit ~30% higher h/s(t) sampled differently

27. Equation of State used in hydro LQCD inspired or parameterized EoS are now standard in hydrodynamic calculations and have improved our understanding of the HBT puzzle (Pratt 2009) and the need to include finite viscosity (Luzum & Romatschke 2008).

28. OK, so what is the viscosity of QGP? • Use hydro with lattice EOS • Set initial energy density to reproduce observed particle multiplicity • Use various values of h/s • Constrain with data • (Account for hadronic state viscous effects with a hadron cascade afterburner)

29. Fluctuations, flow and the quest for h/s arXiv:1105.3928 v2 described by both Glauber and CGC but different values of h/s v3 described only by Glauber breaks degeneracy Theory calculation: Alver et al. PRC82,034913   arXiv:1105.3928 Theory calculation: Alver et al. PRC82,034913   200 GeVAu+Au Lappi, Venugopalan, PRC74, 054905 Drescher, Nara, PRC76, 041903 2 models with Different fluctuations, Eccentricity, r distribution • Glauber • Glauber initial state • /s = 1/4p • MC-KLN • CGC initial state • /s = 2/4p Stefan Bathe for PHENIX, QM2011

30. Initial nucleon positions fluctuate (& flow) v2 v3

31. New questions raised! • At what scales is the coupling strong? • How is equilibration achieved so rapidly? • Nature of QCD matter at low T but high ? • What is the mechanism for quark/gluon-plasma interactions? For the plasma response? • Is collisional energy loss significant? • Is there a relevant (color) screening length? • Are there quasiparticles in the quark gluon plasma? If so, when and what are they?

32. Next step for experiments: • Do even b quarks come to a screeching halt? • Mb ~ 4.2 GeV/c2 • What does b fate tell us about interactions inside? • Improve accelerator luminosity  rarer probes • Add silicon detector arrays around beam pipe to both PHENIX and STAR • Tag displaced vertex to separate • c,b; reconstruct D & B mesons • Lattice studies also underway • Address Q 1,4,6

33. Composite quasiparticles? b/c separation provides the test! High meff  large collisional energy loss R. Kolevatov & U.A. Wiedemann arXiV:0812.0270

34. After 2015: Upgrade PHENIX HCAL x50 acceptance for quarkonia, jets 

35. Is there a relevant screening length? • Plasma: interactions among charges of multiple particles • spreads charge into characteristic (Debye) length, lD • multiple particles inside Debye sphere • they screen each other • plasma size > lD • In strongly coupled plasmas: few (~1-2) particles in Debye sphere • Partial screening -> liquid-like properties • sometimes even crystals! • Test with heavy quark bound states • Do they survive? • All? None? Some? Which size?

36. Debye screening in QCD: a tricky concept • in leading order QCD (O. Philipsen, hep-ph/0010327)

37. don’t give up! ask lattice QCD Karsch, et al. running coupling coupling drops off for r > 0.3 fm

38. J/y vs. system size, √s arXiv:1103.6269 SPS J/y suppression No obvious pattern of the suppression with e, T! Why more suppression at y=2? To understand color screening: study as function of √s, pT, ronium+ d+Au to disentangle cold matter effects

39. Suppression pattern ingredients arXiv:1010.1246 • Color screening • Initial state effects • Shadowing or saturation of • incoming gluon distribution • Initial state energy loss • (calibrate with p+A or d+A) • Final state effects • Breakup of quarkonia due • to co-moving hadrons • Coalescence of q and qbar • at hadronization • (calibrate with A, centrality dependence)

40. Look at higher √s at LHC Low pT • prompt J/y < inclusive? (b states less suppressed) • √s dependence is weak LHC less suppressed! Final state coalescence?

41. Expect if c-cbar pairs numerous or correlated Open charm flows PRL.98: 172301,2007 J/y seems not to So coalescence @ RHIC is not large

42. Please help to understand quantitatively! • Coalescence could be important at LHC • More c-cbar pairs produced. Use b-bar to probe… • Does partial screening preserve correlations, enhancing likelihood of final state coalescence? • arXiV:1010.2735 (Aarts, et al): Υunchanged to 2.09Tc • cb modified from 1-1.5Tc, then free ϒ (2S,3S) suppressed

43. Heavy quark diffusion Ding, et al. arXiV: 1107.0311 J/Y: Not yes/no! Is the correlation gone @ T >1.5 Tc? What happens at 1.0-1.2Tc? Is there observable evidence of partial screening?

44. Outlook • Experiment: use RHIC+LHC to quantify • Properties of the Quark Gluon Plasma • Features of the QCD phase diagram Need help from the lattice community to • Understand onium suppression patterns in terms of medium effects on the correlation -> screening length • Connect lattice results to observables! • Must make sense of observed (non) dependence on √s • Quantify values of QGP transport properties & EOS • Location and signatures of the QCD critical point • Let’s also attack the other hot new questions!

45. New questions raised! • At what scales is the coupling strong? • How is equilibration achieved so rapidly? • Nature of QCD matter at low T but high ? • What is the mechanism for quark/gluon-plasma interactions? For the plasma response? • Is collisional energy loss significant? • Is there a relevant (color) screening length? • Are there quasiparticles in the quark gluon plasma? If so, when and what are they?

46. backup slides

47. strongly coupled dusty plasma B. Liu and J. Goree, cond-mat/0502009 minimum observed in other strongly coupled systems – kinetic part of h decreases with G while potential part increases minimum h at phase boundary? quark gluon plasma Csernai, Kapusta & McLerran PRL97, 152303 (2006)

48. Currently a raging debate • Just WHAT is interacting in the hot dense plasma? • Individual gluons? • Pure fields? • Multi-gluons that continuously • split & re-form? • i.e. composite quasiparticles • (in classical liquids voids fill this role)

49. plasma lives for 3x10-23 s droplet is 10-12 cm across can’t use a thermometer! So we look at the light Hottest Science Experiment on the Planet* * According to Discover Magazine

50. Insights, given first LHC results • Quarkonia energy dependence not understood! • Need charmonium and bottonium states at >1 √s at RHIC • + guidance from lattice QCD! • Jet results from LHC very surprising! • Steep path length dependence of energy loss • also suggested by PHENIX high pT v2; AdS/CFT is right? • Little modification of “jet” fragmentation function • looks different at RHIC (different jet definition, energy) • Lost energy goes to low pT particles at large angle • is dissipation slower at RHIC? Due to medium or probe? • Little modification of di-jet angular correlation • appears to be similar at RHIC • Need full, calorimetric reconstruction of jets in wide y range at RHIC to disentangle probe effects/medium effects/initial state