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Lecture 1 Heavy Ion Collisions: geometry, timescales, and collective behavior

z. y. x. Lecture 1 Heavy Ion Collisions: geometry, timescales, and collective behavior. Barbara Jacak Stony Brook University January 10, 2012. Outline(s ). Lectures on heavy ion collisions and quark gluon plasma Geometry and collective behavior in heavy ion collisions

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Lecture 1 Heavy Ion Collisions: geometry, timescales, and collective behavior

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  1. z y x Lecture 1Heavy Ion Collisions: geometry, timescales, and collective behavior Barbara Jacak Stony Brook University January 10, 2012

  2. Outline(s) Lectures on heavy ion collisions and quark gluon plasma • Geometry and collective behavior in heavy ion collisions • Energy loss and opacity in the quark gluon plasma • Properties of strongly coupled plasmas and what the string theorists tell us • Electromagnetic probes, screening, and QGP outlook TODAY • Introduction and motivation to study the QCD plasma • Stages and timescales in heavy ion collisions • Geometry of the collisions • Collective flow, hydrodynamics, and “the perfect liquid” • Effects of fluctuations

  3. Goal: Create the hottest matter on earth Heat to T > 1012 K last seen: ~ 1 second after the Big Bang! What is it? How does it work? What can we learn about the transition?

  4. Gluon number is not fixed Virtual q-q pairs abundant Inside a nucleon Theorists’ view Experimenter’s view Scatter electrons off a p sln(1/x))n terms x: momentum fraction carried by parton slogQ2)n terms Q2: momentum transfer in a collision

  5. asymptotic freedom At high temperature/density screening by produced colored particles Expect phase transition to deconfined quark gluon plasma Lattice QCD Tc ~ 170 MeV + +… Hot, dense QCD matter • Gluons carry color interact among themselves theory is non-abelian • Curious property at large distance: • confinement of quarks in hadrons

  6. From the practical point of view What we see in the lab: All the particles which come out at the end of the collision

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

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

  9. At the LHC Pb+Pb at 2.76 TeV per NN Also, ATLAS and CMS take data with Pb+Pb

  10. e, pressure builds up Hard scattered q,g (short wavelength) probes of plasma formed p, K, p, n, f, L, D, X, W, d, Hadrons qqq baryons & qq mesons reflect (thermal) properties when inelastic collisions stop Hot QGP thermal radiation (g, g* e+e-, m+m-) heavy ion collision & diagnostics time not possible to measure as a function of time nature integrates over the entire collision history

  11. Questions • Can we create quark gluon plasma in the lab? • thermodynamic properties (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!

  12. study plasma with radiated & “probe” particles • as a function of transverse momentum • 90° is where the action is (max T, r) • pL between the two beams: midrapidity • pT < 1.5 GeV/c • “thermal” particles • radiated from bulk medium • “internal” plasma probes • pT > 3 GeV/c • large Etot (high pT or M) • set scale other than T(plasma) • autogenerated “external” probe • describe by perturbative QCD • control probe: photons • EM, not strong interaction • produced in Au+Au by QCD • Compton scattering

  13. Geometry matters ameter = b Use Glauber model of nucleons in the nucleus calculate # of participant nucleons Npart # of binary NN collisions Ncoll

  14. Glauber model: calculate probabilities Nucleus B Nucleus A bB zB bA b zA volume element in B: dbBdzB volume element in A: dbAdzA Probability of finding a nucleon in volume element B = rB(bB,zB)dbBdzB(rB is nuclear density * nucleons in B)

  15. OK, so what happens when two nuclei collide?NB: b ≠ 0!

  16. Is the expansion hydrodynamical? Model expansion of the system with fluid dynamics Does the matter exhibit collectivity? • Look for collective flow via velocity boosts

  17. z y x Almond shape overlap region in coordinate space Collective motion & elliptic flow (v2) momentum space dN/df ~ 1 + 2 v2(pT)cos (2f) + … hydrodynamics works!

  18. Kolb, et al Hydrodynamics reproduces elliptic flow of q-q and 3q states Mass dependence requires soft EOS, NOT gas of hadrons Surprise: matter flows like a liquid • huge pressure buildup • large anisotropy  it all happens fast • efficient equilibration mechanism?? only works with low viscosity/entropy “perfect” liquid (D. Teaney, PRC68, 2003)

  19. Eccentricity:

  20. Mechanism for fast thermalization? • Must be thermalized in < 1 fm/c! • Otherwise v2 smaller than in the data • Can this be achieved with gg, qg, and qq binary scatterings? • NO! • Making this picture yield sufficient v2, requires boosting the pQCDparton-parton cross sections by a factor of ~50! • Mechanism not known • I’ll discuss some ideas in lecture 3

  21. Elliptic flow scales with number of quarks transverse KE implication: valence quarks, not hadrons, are relevant pressure builds early, dressed quarks are born of flowing field

  22. Example: milk. Liquids with higher viscosities will not splash as high when poured at the same velocity. Good momentum transport: neighboring fluid elements “talk” to each other  QGP is strongly coupled Should affect opacity : e.g. q,g collide with “clumps” of gluons, not individuals small viscosity/entropy was a surprise Viscosity: inability to transport momentum & sustain a wave low viscosity  absorbs particles & transports disturbances Viscosity/entropy near 1/4 limit from quantum mechanics!  liquid at RHIC is “perfect”

  23. pTdependence of v2

  24. √s dependence Quark number Scaling works at √s = 62 @ 17 GeV?

  25. STAR at RHIC Pb+Pb at LHC  similar flow as at 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

  26. Perfect liquid? Quantify viscosity of QGP! • Use hydro with lattice EOS • Set initial energy density to reproduce observed particle multiplicity • Use various values of h/s • Quantum mechanical lower bound is 1/4p • determined with help from AdS/CFT • Constrain with data • (Account for hadronic state viscous effects with a hadron cascade afterburner)

  27.    3-d viscous hydro and RHIC data Answer depends on • Details of hydro code • Viscous correction • Initial conditions • Freezeout particle mix (being addressed) 5) Dynamics at freezeout … /s ≤ 0.08 - 0.16 Glauber CGC Smaller eccentricity Larger eccentricity

  28.   Momentum dependence of viscous correction

  29. Fluctuations matter! • Nucleons move around inside the nucleus -> locations of NN scattering fluctuate -> apparent symmetry effects yielding only even harmonics not realistic arXiv:1109.6289 h/s=0.08 • Reproduce with hydro • IF include fluctuating initial conditions • Provides a tool to better pin down the viscosity/entropy ratio

  30. Higher moments more sensitive to viscosity • Longitudinal expansion at v ~ c • “freezes in” small shape • perturbations • e.g. triangular fluctuations (v3) • Viscosity opposes dissipation! vn(h/s=0.08)/vn(ideal) vn(h/s=0.16)/vn(ideal) arXiv:1109.6289

  31. 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

  32. pT and √sdependence arXiv:1105.3928 Glauber CGC Smaller eccentricity Larger eccentricity v2 v3

  33. At the LHC ALICE v2 v3

  34. Thermal photons also 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 Large flow magnitude is very surprising!

  35. backup slides

  36. 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…

  37. Expect if c-cbar pairs numerous or correlated Open charm flows but J/y does not PRL.98: 172301,2007 So, cc coalescence in final state @ RHIC is not large Higher at LHC?

  38. susceptibilities & net-baryon fluctuations Relation between the baryon susceptibilities, cB, and cumulants of the net-baryon fluctuations

  39. 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)

  40. Barbara Jacak - Lattice 2011

  41. 200GeV Au+Au 20-40% PHENIX Preliminary inc. v2 (2BBC) inc. v2 with external conversion method Direct photon flow ingredients • Key cross checks: ginc are really g’s: check using g-> e+e- Rg for virtual vs. real g

  42. Collisional energy loss? v2 decrease with pT? role of b quarks? heavy quark suppression & flow? PRL.98: 172301,2007 arXiV: 1005.1627

  43. Critical point search: low energy Au+Au @ RHIC S. Gupta, QM2011 Tools: Fluctuations, partonic collective flows

  44. Can we locate the QCD critical point? + deconfinement onset S. Gupta, QM2011

  45. Fluctuations as Critical Point Signature Karsch, et al. PLB 2010.10046 • Event-by-event net-baryon fluctuation ratios from STAR are so far consistent with the Hadron Resonance Gas • Hadronfreezeout not (yet) near critical point • Calculations of higher moments from LQCD deviate from HRG calculations and may provide conclusive evidence for critical point if observed in data

  46. Beam Energy Scan in PHENIX Is there a critical point separating 1st order phase transition & smooth cross-over? • Quark-number scaling of V2 • saturation of flow vs collision energy • find /s minimum at critical point from flow • Critical point searches via: • fluctuations in <pT> & multiplicity • K/π, π/p, pbar/p chemical equilibrium • RAAvss, ….

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