Introduction to Relativistic Heavy Ion Collision Physics

Huan Z. Huang

黄焕中Department of Physics and Astronomy

University of California, Los Angeles

Two Puzzles of Modern Physics

• 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.

-- T.D.Lee李政道

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 !

A Pictorial View of Micro-Bangs at RHIC

Thin PancakesLorentz =100

Nuclei pass thru each other

< 1 fm/c

Huge StretchTransverse ExpansionHigh Temperature (?!)

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 !

initial state

pre-equilibrium

QGP andhydrodynamic expansion

hadronization

hadronic phaseand freeze-out

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

RHIC Complex

STAR

Relativistic Heavy Ion Collider --- RHIC

Au+Au 200 GeV N-N CM energyPolarized p+p up to 500 GeV CM energy

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 q q

q qq q

Quark pairs can be produced from vacuumNo free quark can be observedMomentum Transfer

Co

up

lin

g S

tren

gth

Shorter distance

(GeV)

QCD on Lattice

Transition from quarks to hadrons – DOF !QGP – not an ideal Boltzmann gas !

Lattice: current statusLattice: 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: TC180 MeV

Rajagopal & Wilczek, hep-ph/0011333

Fodor & Katz, hep-lat/0110102

Quark-Hadron Phase Transition

The Melting of Quarks and Gluons-- Quark-Gluon Plasma --

Matter Compression: Vacuum Heating:

High Baryon Density-- low energy heavy ion collisions-- neutron starquark star

High Temperature Vacuum -- high energy heavy ion collisions -- the Big Bang

Deconfinement

Collision Dynamics

Initial Energy Density EstimatePRL 85, 3100 (00); 91, 052303 (03); 88, 22302 (02), 91, 052303 (03)

PHOBOS

hminus:Central Au+Au <pT>=0.508GeV/cpp: 0.390GeV/c

Pseudo-rapidityWithin ||<0.5 the total transverse momentum created is 1.5x650x0.508 ~ 500 GeV from an initial transverse overlap area of R2 ~ 153 fm2 !

Energy density ~ 5-30 0 at early time =0.2-1 fm/c !

19.6 GeV

130 GeV200 GeV

Ideas for QGP Signatures

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 (and anti-particles).

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))

Quark/gluon

Quark/gluon dE/dx in color medium is large!

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 .

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/.

c c Charm quarks c-c may not bindInto J/ in high T QCD medium

The J/ yield may be increased due to charm quark coalescence at the final stage of hadronization (e.g., R.L. Thews, hep-ph/0302050)

1st year detectors

Silicon Vertex Tracker

Central Trigger Barrel

FTPCs

Time Projection Chamber

Barrel EM Calorimeter

Vertex Position Detectors

Endcap Calorimeter

Magnet

Coils

TPC Endcap & MWPC

+ TOF

Silicon Strip Detector

ZDC

2nd year detectors installation in 2002 installation in 2003

ZDC

The STAR Detector