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QCD IN EXTREME CONDITIONS Physics at the Relativistic Heavy Ion Collider

This comprehensive overview delves into the physics of Quantum Chromodynamics (QCD) in extreme conditions, exploring topics such as energy density, partonic energy loss, chiral symmetry, and more at the Relativistic Heavy Ion Collider. Understand the phases of nuclear matter, QCD phase transition, and experimental investigations accessible to study phase transitions. Discover theoretical insights, stages of collisions, equilibration processes, hadronization, and freeze-out scenarios at high energy densities.

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QCD IN EXTREME CONDITIONS Physics at the Relativistic Heavy Ion Collider

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  1. QCD IN EXTREME CONDITIONSPhysics at the Relativistic Heavy Ion Collider Richard Seto University of California, Riverside 2005 CTEQ SCHOOL Puebla Mexico May 21, 2005 (with slides and material stolen from W. Zajc, J. Nagle, …)

  2. Time History of Collision Outline • Introduction • energy density ε, B • The initial state, ε • The (s)QGP • thermalization, ε • viscosity and coupling • Partonic energy loss, ε • Hadronization • Missing pieces/new ideas • Chiral symmetry • Thermalization?

  3. Outline new ways of looking at problems • Introduction • PHYSICS DATA THEORY • energy density ε, B ET Bjorken model • The initial state, εMultiplicity, RdA CGC • The (s)QGP • thermalization, ε Elliptic Flow • viscosity and coupling Elliptic Flow ADS/CFT-blackholes • Partonic energy loss, εpT spectraPQCD • Hadronization particle yield recombination • Missing pieces/new ideas • Chiral symmetry dileptons • Thermalization? blackholes again

  4. In the beginning… g(T) QCD Phase Transition • Early Universe (~1010 years ago) The Early Universe, Kolb and Turner Degrees of Freedom

  5. Origin of (Our) Mass g • The steps represent energy “freezing” into mass The Early Universe, Kolb and Turner Degrees of Freedom X

  6. Quantum ChromoDynamics • QCD : established theory of the strong interaction • quark confinement the non-perturbative structure of the vacuum  responsible for hadronic mass • vacuum structure • modified at high temperatures •  quarks and gluons deconfined at high ______temperatures QCD is a fundamental theory of nature containing a phase transition that is accessible to experimental investigation

  7. 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 Vacuum ~ Baryon Density =0 Phases of Nuclear Matter T Tc

  8. Transition – Sharp Crossover at RHIC That’s OK – 1st order for all practical purposes Sharp Crossover difference between S-B and lattice interactions (in hindsight) Lattice Calculations ~degrees of freedom T Tc Relativistic Heavy Ions RHIC Lattice Calculations: Tc = 170 ± 15% MeV ecritical ~ 0.6 GeV/fm3

  9. RHIC

  10. RHIC FAQ’s • What is RHIC? • Relativistic Heavy Ion Collider • What does it do? • Collides Heavy Ions, Light Ions, protons, polarized protons • To what energy? • 200 GeV x 200 GeV (pp to 500x500) • How does it make heat? • By colliding Heavy ions which leave behind a hot vacuum i.e Baryon number =0

  11. What does a Gold-Gold collision look like?

  12. RHIC’s Experiments STAR

  13. 100 Simulation and model by K. Geiger, …. 10 Energy Density (GeV/fm3) 0.1 0.1 1 10 Time (fm) General Theoretical Picture (?) Stages of the Collision L. McLerran (modified by R.S.) 1 0.1 10

  14. 100 10 Energy Density (GeV/fm3) 0.1 0.1 1 10 Time (fm) Initial State – a CGC • Formation • t~1/Qsat~0.2 fm • CGC-Saturated gluon fields • Hard processes – PQCD • hard probes

  15. 100 10 Energy Density (GeV/fm3) 0.1 0.1 1 10 Time (fm) Equilibration – Elliptic flow starts • Equilibration • t~0.6 fm • Early Thermalization • Strong coupling • Flow (elliptic) develops

  16. 100 10 Energy Density (GeV/fm3) 0.1 0.1 1 10 Time (fm) The strongly-interacting QGP (?) Hard EOS • sQGP • viscocity ~0 • Parton energy loss

  17. 100 10 Energy Density (GeV/fm3) 0.1 0.1 1 10 Time (fm) Mixed Phase-Latent heat-recombination Soft EOS Cross over (wanna be 1st order) • Mixed Phase • Phase Transition (Cross over) • Hadronization-recombination

  18. 100 10 Energy Density (GeV/fm3) 0.1 0.1 1 10 Time (fm) Hadronic phase Hard EOS Hadronic Phase radial flow develops chemical freezeout Tch ~ 160 MeV

  19. 100 10 Energy Density (GeV/fm3) 0.1 0.1 1 10 Time (fm) Freezeout • Kinetic Freezeout • T~130 MeV

  20. “Questions” • Evolution of system • thermal equilibrium? • initial temperature or energy density ? • confinement • signatures of deconfinement seen? • origin of confinement? • the QCD vacuum • connections to the masses of the hadrons? • origin of chiral symmetry breaking? • properties of matter at high energy density?quark and gluon description correct? Where are we?

  21. First - Some general thoughts • Data is in good shape • Redundancy in Experiments is Good BRAHMS, PHENIX, PHOBOS,STAR • Difficulty is often in theoretical interpretation • Advances being made • Interplay between theory and Experiment • finding the “right” way to think about a problem

  22. 1.0 STAR prelim p/p ratio PHENIX preliminary SPS STAR 200 prelim 0.1 ~0.05 AGS ~0.002 √s [GeV] Quantum Numbers of the Vacuum? World s dependence • Baryon number = zero? ~YES

  23. ct0 bjorken energy density • dET/d = 600 GeV (PHENIX) • take  from hydro arguments ~0.6 fm • R~6fm for Au • ~ 9GeV/fm3 @ thermalization pR2 εcritical~0.6 GeV RHIC > critical

  24. The Initial State: A ColoredGlassCondensate? a way to understand gluons at high energy density

  25. proton proton Colored Glass Condensateand the Nucleus as amplifier of gluon density xG(x) x peripheral gluons/area low central high Nucleus xbj: 10-4(p)10-2(Au)

  26. dN/d/ .5Npart CGC- initial state - Saturation in Multiplicity AuAu 130 GeV ε~ 18 GeV/fm3 Kharzeev, Nardi PLB 507, 121 (2001) Npart

  27. Other energies • Data now available from 200, 130 and 19 GeV • Only CGC (Kharzeev, Nardi, Levin) provides consistent description (?!?) saturation at s=20GeV?

  28. Regions of a nucleus(Au) CQF CGC 10-4 look for suppression at higher y QS 10-3 Y~2 BULK x PHENIX/STAR central detectors Y~0 10-2 pQCD y~log(1/x) 10-1 pQCD ΛQCD 1 100 1 10 Q (GeV)

  29. RCP at forward rapidity: Brahms =0 =1 =2.2 =3.2 Suppression at high y as expected in CGC model caveat – data includes protons Kharzeev, Kovchegov, Tuchin hep-ph/0405045

  30. dAu collisions: Brahms Suppression at high y as expected in CGC model caveat – data includes protons similar results from PHENIX Kharzeev, Kovchegov, Tuchin hep-ph/0405045

  31. RCP at forward rapidity: Brahms-charged particles =0 =1 =2.2 =3.2 RCP Suppression at high y as expected in CGC model caveat – data includes protons Kharzeev, Kovchegov, Tuchin hep-ph/0405045

  32. Equilibration?sQGP?Elliptic flow starts? Thermalized Energy density?

  33. z y x  Flow: A collective effect really? • Elliptic flow = v2 = 2nd fourier coefficient of momentum anisotropy • dn/d ~ 1 + 2v2(pT)cos (2 ) + ... • Initial spatial anisotropy converted into momentum anisotropy. • Efficiency of conversion depends on the properties of the medium.

  34. RHIC data • RHIC data: nearing hydrodynamic model prediction with zero viscocity • early thermalization • Hydrodynamics assumes a thermal system • strong coupling • mfp~0 1/S dN/dy (S=area) more central

  35. PHENIX Huovinen et al Why early thermalization? • If system free streams • spatial anisotropy is lost • v2 is not developed • detailed hydro calculations (QGP+mixed+RG, zero viscosity) • therm ~ 0.6 -1.0 fm/c • ~15-25GeV/fm3 • (ref: cold matter 0.16 GeV/fm3) (Teany et al, Huovinen et al)

  36. Los Angles Times – May 2005 WHAT?! Flow, Hydrodynamics, Viscosity, Perfect Fluds…. ? YUK! and String Theory

  37. Fluids: Ask Feynman ( from Feynman Lecture Vol II) • The subject of the flow of fluids, and particularly of water, fascinates everybody….we watch streams, waterfalls, and whirlpools, and we are fascinated by this substance which seems almost alive relative to solids. …. • The subject of the flow of fluids, and particularly of water, fascinates everybody…. Surely you’re joking Mr. Feynman

  38. [ ] Viscosity and the equation of fluid flow =density of fluid =potential (e.g. gravitational-think mgh) v=velocity of fluid element p=pressure Sheer Viscocity Bernoulli

  39. [ ] Non-ZERO Viscosity smoke ring diffuses smoke ring dissipates

  40. [ ] ZERO Viscosity does not diffuse smoke ring keeps its shape Viscosity dissipates momentum note: you actually need viscosity to get the smoke ring started

  41. Anisotropic Flow • Conversion of spacial anisotropy to momentum anisotropy depends on viscosity • Same phenomena observed in gases of strongly interacting atoms (Li6) M. Gehm, et alScience 298 2179 (2002) strongly coupled viscosity=0 weakly coupled finite viscosity The RHIC fluid behaves like this, that is, viscocity~0

  42. Can we anyone calculate the viscosity?A primer on viscosity (Feynam again) the low-brow sheer force(stress) is: energy momentum stress tensor

  43. Using Maldecena 10-D string theory magici.e. AdS/CFT duality Gravity “QCD” “QCD” strong coupling N=4 supersymmetry ~ almost QCD “SYM” (OK the coupling constant doesn’t run, but I am interested in the strong coupling case, there are a bunch of extra particles so we will divide by the entropy to get rid of the extra DOF…) Gravity dual Policastro, Son, Starinets hep-th 0104066 “The key observation… is that the right hand side of the Kubo formula is known to be proportional to the classical absorption cross section of gravitons by black three-branes.” σ(0)=area of horizon

  44. finishing it up Entropy black hole “branes” Entropy “QCD”  Area of black hole horizon Entropy black hole Bekenstetein, Hawking = Kovtun, Son, Starinets hep-th 0405231

  45. viscocity~0, i.e. A Perfect Fluid? RHIC ~ 1? JPG, 30(2004) 1221 viscosity bound? nitrogen helium water • See “A Viscosity Bound Conjecture”, P. Kovtun, D.T. Son, A.O. Starinets, hep-th/0405231 • THE SHEAR VISCOSITY OF STRONGLY COUPLED N=4 SUPERSYMMETRIC YANG-MILLS PLASMA., G. Policastro, D.T. Son , A.O. Starinets, Phys.Rev.Lett.87:081601,2001 hep-th/0104066 lowest viscosity possible?

  46. Real QCD from the Lattice helium nitrogen water Nakamura and Sakai hep-latt/0406009

  47. RHIC data: nearing hydrodynamic prediction with zero viscosity early thermalization strong coupling Old picture short screening length screening length q q A strongly Interacting QGP? weakly coupled QGP?

  48. RHIC data: nearing hydrodynamic prediction with zero viscosity early thermalization strong coupling New picture Long screening length Long range correlations screening length q q A strongly Interacting QGP sQGP New Lattice Data J//ψ stays together at > TC F. Karsch et al, Journal of Physics G 30 (2004) 887

  49. strongly interacting QGP??? partonic energy loss Hard probes

  50. The experiment we would like to do – Deep Inelastic Scattering of the QGP “hard” probes Formed in initial collision with high Q2 penetrate hot and dense matter sensitive to state of hot and dense matter dE/dx by strong interaction  jet quenching Hard Probes In Heavy Ion Collisions, aka Jet quenching Beams of colored quarks Colorless Hadrons Colored QGP hadronic phase and freeze-out QGP and hydrodynamic expansion Hard parton Softened Jet pre-equilibrium hadronization

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