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Introduction to Relativistic Heavy Ion Collision Physics

Introduction to Relativistic Heavy Ion Collision Physics. Huan Z. Huang 黄焕中 Department of Physics and Astronomy University of California, Los Angeles Oct 2006 @Tsinghua. http://hep.tsinghua.edu.cn/talks/Huang/. Two Puzzles of Modern Physics. -- T.D.Lee.

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Introduction to Relativistic Heavy Ion Collision Physics

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  1. Introduction to Relativistic Heavy Ion Collision Physics Huan Z. Huang 黄焕中 Department of Physics and Astronomy University of California, Los Angeles Oct 2006 @Tsinghua http://hep.tsinghua.edu.cn/talks/Huang/

  2. Two Puzzles of Modern Physics -- T.D.Lee • Missing Symmetry – all present theories are based on symmetry, but most symmetry quantum numbers are NOT conserved. • Unseen Quarks – all hadrons are made of quarks, yet NO individual quark has been observed.

  3. Vacuum As A Condensate • Vacuum is everything but empty! • The complex structure of the vacuum and the response of the vacuum to the physical world breaks the symmetry. • Vacuum can be excited! We do not understand vacuum at all !

  4. A Pictorial View of Micro-Bangs at RHIC Huge Stretch Transverse Expansion High Temperature (?!) Nuclei pass thru each other < 1 fm/c Thin Pancakes Lorentz g=100 The Last Epoch: Final Freezeout-- Large Volume Au+Au Head-on Collisions  40x1012 eV ~ 6 micro-Joule Human Ear Sensitivity ~ 10-11 erg = 10-18 Joule A very loud Bang, indeed, if E Sound…… Vacuum Engineering !

  5. hadronic phase and freeze-out QGP and hydrodynamic expansion initial state pre-equilibrium hadronization High Energy Nucleus-Nucleus Collisions Physics: 1) Parton distributions in nuclei 2) Initial conditions of the collision 3) a new state of matter – Quark-Gluon Plasma and its properties 4) hadronization

  6. Kinematic Variables Rapidity: Pseudo-rapidity: Transverse Momentum: Transverse Mass:

  7. Useful Expressions Feymann xF: Bjorken x: Light-cone x+:

  8. Cross Sections Number of Reactions sTotal = Number of Beam Particles X Scattering Center / Area Dimension [L2] sTotal = sinel + sel SD: Singly Diffractive ND: Non-Diffractive sinel= sSD + sND Differential Cross Section: Question: differential cross section vs total cross section?

  9. Invariant Cross Sections Invariant Differential Cross Section: E d3s/d3p  Invariant Multiplicity Density: E d3n/d3p  Experimental Considerations: Efficiency, Acceptance, Decay Correction, Target-out Correction.

  10. Order of Magnitude Geometrical CS: pp pr2 = p(1fm)2 = 32 mb Au+Au Collisions: Rau = 1.2 A1/3 = 6.98 fm pbmax=p(2R)2 = 6 barn 1 barn = 10-24 cm2 Regge Theory: stotal=XS0.0808 + YS-0.4525 p-pbar 21.70 98.39 mb p-p 21.70 56.08 mb Pomeron r,w,f,a,…. HIJING: minijet production

  11. Luminosity at Collider NB2 B v / U L = A B  Number of bunches per beam NB Number of particles per bunch v  velocity of particles U  circumference of the ring A  beam cross section at the collision Relativistic Heavy Ion Collider: eN Invariant Transverse 95% Emittance b* the beta function

  12. RHIC Numbers RHIC Design: Au Beam proton Beam B 57 NB 109 1011 L 2x1026 1x1031 cm-2s-1 200 GeV 500 GeV Collision Rate: L x s 1200 Hz 0.7 MHz

  13. RHIC Complex

  14. STAR Relativistic Heavy Ion Collider --- RHIC Au+Au 200 GeV N-N CM energy Polarized p+p up to 500 GeV CM energy

  15. Mesons Exotics (q-q) (qqqq-q,…) Building Blocks of Hadron World Molecules Atoms Nucleus Electrons Proton Neutron Hyperons (uud) (udd) (s…) Strong interaction is due to color charges and mediated by gluons. Gluons carry color charges too. Baryon Density: r = baryon number/volume normal nucleus r0 ~ 0.15 /fm3 ~ 0.25x1015 g/cm3 Temperature, MeV ~ 1.16 x 1010 K 10-6 second after the Big Bang T~200 MeV

  16. Energy Scale and Phase Transition Entity Energy Dimension Physics Bulk Property P/T Atom 10’s eV 10-10 m Ionization e/Ion Plasma No Nucleus 8 MeV 10-14 m Multifrag. Liquid-Gas Y(?) QCD 200 MeV 10-15 m Deconfine. QGP Y(?) EW 100 GeV 10-18 m P/CP Baryon Asymmetry Y(?) GUT 1015-16 GeV Supersymmetry TOE 1019 GeV Superstring

  17. Coupling Strength q q Shorter distance  q q q q (GeV) Momentum Transfer Salient Feature of Strong Interaction Asymptotic Freedom: Quark Confinement: 庄子天下篇 ~ 300 B.C. 一尺之棰，日取其半，万世不竭 Take half from a foot long stick each day, You will never exhaust it in million years. QCD Quark pairs can be produced from vacuum No free quark can be observed

  18. QCD on Lattice Transition from quarks to hadrons – DOF ! QGP – not an ideal Boltzmann gas !

  19. Rajagopal & Wilczek, hep-ph/0011333 Lattice: current status • technical progress: finer mesh size, physical quark masses, improved fermion actions • phase-transition: smooth, rapid cross-over • EoS at finite μB: in reach, but with large systematic uncertainties • critical temperature: TC180 MeV Fodor & Katz, hep-lat/0110102

  20. Quark-Hadron Phase Transition

  21. QGP – micro-second after the Big Bang

  22. The Melting of Quarks and Gluons-- Quark-Gluon Plasma -- Matter Compression: Vacuum Heating: Deconfinement High Temperature Vacuum -- high energy heavy ion collisions -- the Big Bang High Baryon Density -- low energy heavy ion collisions -- neutron starquark star

  23. early universe 250 RHIC quark-gluon plasma 200 SPS AGS Chemical Temperature Tch [MeV] Lattice QCD deconfinement chiral restoration 150 thermal freeze-out SIS 100 hadron gas neutron stars atomic nuclei 50 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] 0 QCD Phase Transition What do experimental data points indicate and how were these points obtained ?

  24. Number of Participants Impact Parameter Particle Production is assumed to be directly related to the impact parameter or number of participant nucleons. Nuclear Collision Geometry

  25. Number of Participant Nucleons • Geometrical Interpretation of Observables • A monotonic relation between the observable and • collision centrality is assumed • b) Estimate from direct measurement • missing energy from Zero-degree calorimeter • from dn/dy of protons….

  26. ET EZDC ET Directly Determining NPART Best approach (for fixed target!): • Directly measure in a “zero degree calorimeter” • (for A+A collisions) • Strongly (anti)-correlated with produced transverse energy: NA50

  27. Number of Participant Nucleons c) Dynamical Model Tune to fit experimental measurement From model to convert measurement to impact parameter and number of participant nucleons ++ Fluctuations are included - - Physical picture is biased to begin with

  28. Spectrum Fit mT spectrum: d2n/(2pmT)dmTdy vs (mT-m0) pT spectrum: d2n/(2ppT)dpTdy vs pT Boltzmann mT Fit: d2n/(2pmT)dmTdy ~ mT exp(-mT/slp) slp  Slope Parameter Why is this Boltzmann? d3n/d3p ~ exp(-E/T) Invariant Multiplicity Density: Ed3n/d3p ~ E exp(-E/T) E = mTcosh(y-ycm) d2n/(2pmT)dmTdy ~ mT cosh(y-ycm) exp(-mT cosh(y-ycm)/T) Slp depends on rapidity for an isotropic thermal fireball slp = T/cosh(y-ycm) dn/dy = sy ~ 0.7-0.8

  29. mid-rapidity Tp = 565 MeV TK = 300 MeV Tp = 190 MeV Naïve Expectations • Thermal Isotropic Source  mT Scaling p, K and proton have the same slope parameter e-E/T Data show a large difference among these particles  Expansion

  30. Naïve Expectation 2 Slope parameter  Temperature Rapidity density dn/dy  entropy or energy density First Order Phase Transition: <pT> QGP Mixed hadron dn/dy Collision dynamics much more complicated !!

  31. Collision Dynamics

  32. Bjorken Scaling Bjorken Ansatz: “…… at sufficient high energy there is a ‘central-plateau’ structure for the particle production as a function of the rapidity variable.” dn/dy y Physics must be invariant under Lorentz-boost: 1) Local thermodynamic quantity must be a function of proper time only. 2) Longitudinal velocity vz = z/t or y = 0.5 ln ((t+z)/(t-z))

  33. mT dn/dy At Bjorken Energy Density E x DN Energy density e = A x Dz E  average energy per particle A  transverse area of the collision volume Dz  longitudinal interval DN  number of particles in Dz interval vz = z/t = tanh y; z = t sinh y Dz = t cosh y Dy E = mT cosh y mT cosh y DN e = A t cosh y Dy

  34. Initial Energy Density Estimate PRL 85, 3100 (00); 91, 052303 (03); 88, 22302 (02), 91, 052303 (03) 200 GeV 130 GeV PHOBOS 19.6 GeV Pseudo-rapidity Within |h|<0.5 the total transverse momentum created is 1.5x650x0.508 ~ 500 GeV from an initial transverse overlap area of pR2 ~ 153 fm2 ! hminus: Central Au+Au <pT>=0.508GeV/c pp: 0.390GeV/c Energy density e ~ 5-30 e0 at early time t=0.2-1 fm/c !

  35. Parton Energy Loss in a QCD Color Medium: (J.D. Bjorken Fermilab-pub-82-059 (1982) X.N. Wang and M. Gyulassy, PRL 68, 1480 (1992)) Strangeness Production:(J.Rafelski and B. Muller PRL 48, 1066 (1982)) s-s quark pair production from gluon fusions in QGP leads to strangeness equilibration in QGP  most prominent in strange hyperon production (L,X,W and anti-particles). Quark/gluon dE/dx in color medium is large! Quark/gluon Ideas for QGP Signatures

  36. QCD Color Screening:(T. Matsui and H. Satz, Phys. Lett. B178, 416 (1986)) A color charge in a color medium is screened similar to Debye screening in QED  the melting of J/y. Charm quarks c-c may not bind Into J/y in high T QCD medium c c The J/y yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050) Ideas for QGP Signatures Chiral Symmetry Restoration: T = 0, m(u,d,s) > 0 – Spontaneous symmetry breaking T> 150 MeV, m=0 – Chiral symmetry restored Mass, width and decay branching ratios of resonances may be different in dense medium .

  37. F. Weber J.Phys. G27 (2001) 465 Models of Neutron Stars “Strangeness" of dense matter ? In-medium properties of hadrons ? Compressibility of nuclear matter ? Deconfinement at high baryon densities ?

  38. The STAR Detector Magnet Time Projection Chamber FTPCs Endcap Calorimeter 1st year detectors 2nd year detectorsinstallation in 2002 installation in 2003 Coils TPC Endcap & MWPC Silicon Vertex Tracker Silicon Strip Detector ZDC ZDC Vertex Position Detectors Barrel EM Calorimeter Central Trigger Barrel + TOF RICH

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