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Richard Seto University of California, Riverside RHIC/STAR Workshop Bejing, PRC August 29-31, 2002

RHIC: an Overview. QCD and the Vacuum. Richard Seto University of California, Riverside RHIC/STAR Workshop Bejing, PRC August 29-31, 2002. Is it Interesting?. Where Does Mass come from?. Massive quark?. Massive quarks in lite QCD? (u,d) Chiral (R-L) Symmetry Massless quarks!

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Richard Seto University of California, Riverside RHIC/STAR Workshop Bejing, PRC August 29-31, 2002

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  1. RHIC: an Overview QCD and the Vacuum Richard Seto University of California, Riverside RHIC/STAR Workshop Bejing, PRC August 29-31, 2002

  2. Is it Interesting?

  3. Where Does Mass come from? Massive quark? • Massive quarks in lite QCD? (u,d) • Chiral (R-L) Symmetry • Massless quarks! • So Where does mass come from?

  4. The Vacuum: Source of Mass Massless quarks • Start at high Temperature with massless quarks

  5. The Vacuum: Source of Mass T>Tc T>Tc Massless quarks T<Tc V()  T~Tc High Temperature Low • Start at high Temperature with massless quarks • Assume a background field = •  - goo of quarks and gluons • Similar to the higgs field for E-W theory • Couples to quarks(massless for now) and gluons • Potential term for  has special Temperature Dependence

  6. The Vacuum: Source of Mass T~Tc T>Tc T>Tc Massless quarks T<Tc V()  T~Tc High Temperature Low • As Temperature Cools past Tc

  7. The Vacuum: Source of Mass T~Tc T~Tc T>Tc Condensate T<Tc T<Tc V()  T~Tc High Temperature Low • As Temperature Cools past Tc • Spontaneous symmetry breaking (I.e. chiral) of the quark condensate at low Temperature generates hadron masses

  8. Weird! The idea that empty space should be full of complicated material is wilder than many crackpot theories, and more imaginative than most science fiction… • F. Wilczeck in Physics Today (April 1998)

  9. Living in the cold QCD vacuum • It is generally believed in the fish population that there is an inherent resistance to motion and that they swim in a “vacuum”. The vacuum – perceived to be empty by the general fish population

  10. A clever (and crazy idea) • One clever young fish is enlightened. “The vacuum is complicated and full of water!” he says –” really there is no resistance to motion!” • “Phooey” say his friends, “we all know the vacuum is empty.”

  11. How does he prove it? • Answer – he builds a machine to boil the water into steam – to “melt” the vacuum • In steam his “friends” move freely. • OK OK – they die because • They can’t breathe in air • They are poached because of the heat • So maybe he boils only what’s in a small bottle as an experiment, and he calls this machine RICC (Relativistic Ice Cube Collider… • you get the point…

  12. The HOTQCD vacuum • Can you create it? • YES! AT RHIC • RHI collision leaves a region of excited qq and gluons – ie hot vacuum

  13. What is the hot vacuum like? • How hot is it? (Temperature) • How sticky is it? (Energy Loss – aka Jet quenching) • How much energy can it store? (Latent heat) • What is its equation of state? • What is (are) the phase transition(s) to a cold vacuum like? • 1st, 2nd order, cross over? • How does it generate mass? • How/why does it confine? • What interesting properties does it exhibit? • …

  14. Why is it timely • Theory + Experiment = Understanding • Theoretical Calculations in regions probed by experiment • Experiments inregions calculable by theory • New era of Precision • Precision Calculations • Precision Measurements • Precision Detectors • Redundancy of measurements (4 detectors!) • AA, pA (dA), pp, eA

  15. Phases of Nuclear Matter TWO phase transitions! Thedeconfinement transition - particles are roam freely over large volume The chiral transition - masses change All indications are that these two are at or are very nearly at the same TC T Tc

  16. Lattice Calculations Transition – Sharp Crossover at RHIC That’s OK – 1st order for all practical purposes 0.5 4.5 15 35 75 GeV/fm3 e/T4 Sharp Crossover Lattice Results Tc(Nf=2)=1738 MeV Tc(Nf=3)=1548 MeV Critical point T/Tc (F. Karsch, hep-lat/9909006) 1st order T Tc Lattice Calculations: Tc = 170 ± 15% MeV ecritical ~ 0.6 GeV/fm3

  17. Stages of the Collision • Various stages • Must be described using different physics • Hard • Soft • Detectors see sum of all phenomena • Importance of hard probes • Keep an open mind –no single idea (or theorist) can explain everything

  18. Data • 4 detectors • STAR – Large acceptance • PHENIX – photons, leptons • PHOBOS – small, low-pt • BRAHMS – small, high y • Runs • 130 GeV run • 200 GeV run – results from recent QM

  19. Is it like the Vacuum?

  20. Quantum Numbers of the Vacuum? World s dependence • Baryon number = zero? 1.0 STAR prelim p/p ratio PHENIX preliminary SPS STAR 200 prelim 0.1 ~0.05 Note: Thermal fit B~30 MeV AGS ~0.002 ~YES √s [GeV]

  21. How Hot is it? Is it Hot enough?

  22. dET/dy ~ The Initial Energy Density eBj~ 26.0 GeV/fm3 pR2 eBj~ 5.2 GeV/fm3 ct0 Lattice ec ~6.5 fm Thermalization time ? PHENIX: Central 200 GeV Au Au High Initial energy density-Its “HOT “enough! Remember, from the Lattice T = 150-200 MeV e ~ 0.6-1.8 GeV/fm3

  23. You said theory was getting better. Can you make reliable calculations of the initial conditions?

  24. The Colored Glass CondensateA layman’s view xG(x) x High x • QCD - Notoriously hard to calculate • Regime where QCD simplifies: High Gluon Densities at low-x • gluons ~ x- ,i.e. there are more of them as you go to lower x • They begin to overlapGluons saturate • Classical Approx (McLerran, Venogopolan etc) • Robust calculations in QCD using “renormalization group” methods • Depends on a single scale low x QS2=(1/R2)(dNgluon/dy) ~ 2-D gluon density At RHIC, QS~1-2 GeV

  25. The Approximation The Approx Non-perturbative (high density) Small coupling Requires S(QS) to be “small” Expected to fail for QS small Low enegy Peripheral High y Running of S S RHIC 130 central Qs At RHIC, QS~1-2 GeV S(QS)~0.3 –0.4

  26. Why “Colored Glass Condensate?” Spin Glass W….o…r… k … W . . “frustrated” • Colored? - Gluons are colored • Condensate? • Gluons are interacting bosons and fill up the available states • Glass? - A glass is a material with • A long time scale ~ Window glass • induced by “frustration” • In Color Condensate we have “relativistic frustration” • Model Break Nucleus into Gluon Field, and Source • “Source” – quarks and gluons at high-x, Lorenz time dialatedclock runs slow • Gluon field at low-x. Clock runs fast, but motion is governed by “source”. They are “frustrated” “happy” Work Work Work Work Happy Hard working Gluons quark Frustrated Gluons Time dialted quark

  27. Calculations (post-diction) • dN/dy for s, centrality, y, A energy in terms of one variable: QS. • Set QS at a single point • QS larger – more central, higher energy, mid-rapidity • A constant C=CLCMult must be set • CL is gluon liberation coeefficient – probablility that a virtual gluon becomes “real” upon collision (can be calculated on the Lattice) • Cmult is the gluon multiplication coefficent from final state interations • We would like this to be >1, otherwise thermalization produces no new particles • One to one correspondence between gluons and final state particles (I.e. entropy conserved)

  28. Does it work? energy density ~18GeV/fm3 Kharzeev & Levin, nucl-th/0108006 Schaffner-Bielich et al, nucl-th/0108048 Does this explain why dN/dy is less than we might have thought? dNch/dh/(0.5Np) Np Saturation models can predict the scaling with centrality and rapidity! Kharzeev/Levin

  29. Dependence on NpartS, y? • QS depends on Npart, S, y • If S did not run, there would be no dependence!

  30. Prediction at 200 GeV beautiful 0-6% Kharzeev/Levin 15-25% 35-45% 

  31. Prediction at 22 GeV 0-6%  15-25% 35-45% 0-6% 15-25% 35-45% • Do we expect it to work? • At low energy QS becomes small  S large • Expected to fails first for • Peripheral • High y Fails(worst for peripheral, high y) 2 All data PHOBOS Preliminary 1  Np 0 100 200 300 400

  32. Is it thermalized? When? … it better be early, before hadronization, if you are interested in a QGP…

  33. Azimuthal anisotropy: v2 “Elliptic flow” y Momentum space: final asymmetry Coordinate space: initial asymmetry • Late equilibration i.e. free streaming in early stages causes almond shape to become spherical • Strong elliptic flow  Early thermalization py multiple collisions (pressure) px x

  34. Elliptic Flow RHIC: Very strong elliptic flow • Hydrodynamical model (Kolb et al) • Good pt<2, more central • Rapid thermalization • 0 ~ 0.6 fm/c • ~20 GeV/fm3 (possibly later if some comes from CGC?)

  35. Flow of Identified Particles Preliminary • Mass dependence at low pT is well described by hydro (lines, P. Huovinen)

  36. What about Chemical and Thermal Equilibrium? (at freezout)

  37. What have we measured? Global Features:Chemical Equilibration Particle Ratios Model assuming Chemical Equilibration describes yields Pretty well  s ~ 1 Central events From yields, 130 GeV Tch freezeout=177 MeV Baryon=36 MeV

  38. Is it themalized? Themal Model fit Kinetic Freezout 130 GeV STAR 200 K* From inverse slopes Tthermal freezout ~ 130 GEV ~AGS/SPS As at SPS Strange particles Freeze out earlier Omegas freeze-out differently? radial increases to ~ 0.5 Explosive radial expansion high pressure

  39. You’ve talked about the initial state, and the final state. What about the stuff in the Middle? Do you have a QGP?

  40. Hard Probes, aka Jet quenching Deep Inelastic Scattering of the QGP? “hard” probes Formed in initial collision penetrating sensitive to state dE/dx by strong interaction jet quenching Jets by leading particles Look fora suppression of high pT hadron production. Beams of colored quarks Colorless Hadrons Colored QGP

  41. Scaling from pp to AA • Low pT • Thermal • Hydro(Flow) • Exponential in MT • Npart Scaling Nbinary at high pT • High pT • Jetlike • Jet frag • (No flow) • Pwr law in pT • Nbin Scaling Transition ~ 2 –4 GeV? Npart at low pT

  42. Does anythingscale with binaries? • Single electrons from charm (a hard process?) • Fit to pythia charm scaled with BINARIES • Looks like it works! • (with apologies to the great work on charm production-note “dead cone effect”)

  43. Models – scaling pp to AA • pp effects • Intrinsic kT • pp to pA effects • “Cronin effect”, initial state quark scattering i.e. pT broadening Enhances higher pT • Nuclear shadowing • Gluon shadowing • is not measured • large role at RHIC Measure pA at RHIC!

  44. Central Consistent with Ncoll scaling Scale up with Ncoll=12.3 0-10% CENTRAL Ncoll =975±94 70-80% PERIPHERAL Ncoll =12.3 ±4.0 • Central: • Consistent with Ncoll scaling • Peripheral: • Consistent with Ncoll scaling PHENIX Preliminary Consistent with Ncoll scaling

  45. Nuclear Modification Factor SPS – shows Cronin Effect RHIC – Run 1 (130 GeV) RHIC – Run 2 200 GeV) 0-10%  Effect of nuclear medium on yields Run 2 Data Shows a many Sigma Effect! (dE/dx)initial~7 GeV/fm 15x Cold matter (Hermes)

  46. Nuclear Modification Factor RHIC central -Suppression peripheral – Ncoll scaling • Effect of nuclear medium on yields • Comparison of peripheral to central PHENIX Preliminary 70-80% binary scaling 0-10%

  47. Centrality Dependence of RAA Smoothly varies with centrality PHENIX Preliminary PHENIX Preliminary • Smoothly varies with centrality • Dependence changes with pt?

  48. How does Jet energy loss depend on energy, path length etc?

  49. What can we learn? Types of energy loss Constant (probably not physical) QCD motivated Bethe-Heitler (BH) type dE/dx~E LPM type dE/dx~ L ~E gluon coherence>MFP or Egluon>Ecr~pT,gluon2 MFP 5 GeV at RHIC (?) Static and Expanding plasma considered Can learn about Energy loss mechanism Density of gluons L dependence … BH MFP coh LPM

  50. Phase transition from quench? Ideal QGP Phase Transition? Energy Loss Coefficient (GeV2/fm) Massless pion gas Nuclear Matter Energy Density (GeV/fm3) • Calculate q from QGP, pion gas • Jet quenching • sensitive to energy density • NOT phase transition? • But this calculation does not have confinement, chiral symmetry restoration… BDMS

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