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The Quark-Gluon Plasma. Marco van Leeuwen. Elementary particles. Standard Model: elementary particles. Quarks: Electrical charge Strong charge (color). up charm top down strange bottom. +anti-particles. Leptons: Electrical charge. electron Muon Tau n e n m n t.

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the quark gluon plasma

The Quark-Gluon Plasma

Marco van Leeuwen

elementary particles
Elementary particles

Standard Model: elementary particles


Electrical charge

Strong charge (color)

up charm top

down strange bottom



Electrical charge

electron Muon Tau


photon EM force

gluon strong force

W,Z-boson weak force

Force carriers:


Electronelementary, point-particle

Protons, neutrons

Composite particle

 quarks

EM force binds electronsto nucleus in atom

Strong force binds nucleonsin nucleus and quarks in nucleons

qcd and hadrons
QCD and hadrons

Quarks and gluons are the fundamental particles of QCD

(feature in the Lagrangian)

However, in nature, we observe hadrons:

Color-neutral combinations of quarks, anti-quarks

Baryon multiplet

Meson multiplet



I3 (u,d content)

I3 (u,d content)

Mesons: quark-anti-quark

Baryons: 3 quarks

seeing quarks and gluons
Seeing quarks and gluons

In high-energy collisions, observe traces of quarks, gluons (‘jets’)

how does it fit together
How does it fit together?

S. Bethke, J Phys G 26, R27

Running coupling:

as decreases with Q2

Pole at m = L

LQCD ~ 200 MeV ~ 1 fm-1

Hadronic scale

asymptotic freedom and pqcd
Asymptotic freedom and pQCD

At high energies, quarks and gluons are manifest

At large Q2, hard processes: calculate ‘free parton scattering’

+ more subprocesses

low q 2 confinement
Low Q2: confinement

a large, perturbative techniques not suitable

Bali, hep-lat/9311009

Lattice QCD: solve equations of motion (of the fields) on a space-time lattice by MC

Lattice QCD potential

String breaks, generate qq pair to reduce field energy

qcd matter
QCD matter

Energy density from Lattice QCD

g: deg of freedom

Nuclear matter

Quark Gluon Plasma

Bernard et al. hep-lat/0610017

Tc ~ 170 -190 MeV

ec ~ 1 GeV/fm3

Deconfinement transition: sharp rise of energy density at Tc

Increase in degrees of freedom: hadrons (3 pions) -> quarks+gluons (37)

qcd phase diagram
QCD phase diagram

Quark Gluon Plasma

(Quasi-)free quarks and gluons




Early universe

Confined hadronic matter

High-density phases?

Elementary collisions

(accelerator physics)

Neutron stars

Nuclear matter

Bulk QCD matter: T and mB drive phases

heavy ion collisions
Heavy ion collisions

Lac Leman

Lake Geneva

Geneva airport


Meyrin site

Collide large nuclei at high energy to generate high energy density

 Quark Gluon PlasmaStudy properties

RHIC: Au+Au sNN = 200 GeV

LHC: Pb+Pb √sNN≤ 5.5 TeV

27 km circumference

nuclear geometry n part n bin l e
Nuclear geometry: Npart, Nbin, L, e




Npart: nA + nB (ex: 4 + 5 = 9 + …)

Nbin: nA x nB (ex: 4 x 5 = 20 + …)

  • Two limits:
  • - Complete shadowing, each nucleon only interacts once, s Npart
  • No shadowing, each nucleon interact with all nucleons it encounters, s  Nbin
  • Soft processes: long timescale, large s,stot Npart
  • Hard processes: short timescale, small s, stot Nbin

Transverse view

Density profile r: rpart or rcoll



Path length L, mean <L>

centrality examples
Centrality examples

... and this is what you see in a presentation




This is what you really measure

centrality dependence of hard processes
Centrality dependence of hard processes

Total multiplicity: soft processes

Binary collisions weight

towards small impact parameter


200 GeV Au+Au

  • Rule of thumb for A+A collisions (A>40)
    • 40% of the hard cross section is contained in the 10% most central collisions
selected topics in heavy ions
Selected topics in Heavy Ions
  • Elliptic flow
    • Bulk physics, low pT, expansion driven by pressure gradients
  • Parton energy loss
    • High-energy parton ‘probes’ the quark gluon plasma
    • Light/heavy flavour
collective motion
Collective Motion

Only type of collective transverse motion in central collision (b=0) is radial flow.

Integrates pressure history over complete expansion phase

Elliptic flow, caused by anisotropic initial overlap region (b > 0)

More weight towards early stage of expansion (the QGP phase)

forming a system and thermalizing
Forming a system and thermalizing

Animation: Mike Lisa

1) Superposition of independent p+p:

momenta pointed at random

relative to reaction plane


forming a system and thermalizing1
Forming a system and thermalizing

Animation: Mike Lisa

1) Superposition of independent p+p:


density / pressure

at center

momenta pointed at random

relative to reaction plane

2) Evolution as a bulksystem

Pressure gradients (larger in-plane) push bulk “out” “flow”

“zero” pressure

in surrounding vacuum

more, faster particles seen in-plane


how does the system evolve
How does the system evolve?











-RP (rad)

-RP (rad)

1) Superposition of independent p+p:

momenta pointed at random

relative to reaction plane

2) Evolution as a bulksystem

Pressure gradients (larger in-plane) push bulk “out” “flow”

more, faster particles seen in-plane

Animation: Mike Lisa

energy dependence of flow
Energy dependence of flow
  • Flow at RHIC consistent with ideal hydrodynamics!! … so what will we get at LHC ?

NA49, PRC68, 034903

hard probes of qcd matter
Hard probes of QCD matter

Use ‘quasi-free’ partons from hard scatterings

Calculable with pQCD

to probe ‘quasi-thermal’ QCD matter

Quasi-thermal matter: dominated by soft (few 100 MeV) partons

Interactions between parton and medium:

  • Radiative energy loss
  • Collisional energy loss
  • Hadronisation: fragmentation and coalescence

Sensitive to medium density, transport properties

energy loss in qcd matter
Energy loss in QCD matter

radiated gluon

propagating parton


QCD bremsstrahlung(+ LPM coherence effects)

Transport coefficient


Energy loss

Energy loss probes:

Density of scattering centers:

Nature of scattering centers, e.g. mass: radiative vs elastic loss

Or no scattering centers, but fields  synchrotron radiation?

p 0 r aa high p t suppression
p0 RAA – high-pT suppression

: no interactions

RAA = 1

Hadrons: energy loss

RAA < 1

: RAA = 1

0: RAA≈ 0.2

Hard partons lose energy in the hot matter

two extreme scenarios
Two extreme scenarios

Scenario I

P(DE) = d(DE0)

Scenario II

P(DE) = a d(0) + b d(E)

1/Nbin d2N/d2pT

‘Energy loss’



Downward shift


Shifts spectrum to left


P(DE) encodes the full energy loss process

Need multiple measurements to distentangle processes

RAA gives limited information

r aa at lhc



T. Renk, QM2006



S. Wicks, W. Horowitz, QM2006

LHC: typical parton energy > typical E

Expected rise of RAA with pT depends on energy loss formalism

Nuclear modification factor RAA at LHC sensitive to radiation spectrum P(E)

  • Elementary particles of the strong interaction (QCD): quarks and gluon
  • Bound states: p, n, p, K (hadrons)
  • Bulk matter: Quark-Gluon-Plasma
    • High T~200 MeV
  • Heavy ion collisions:
    • Produce and study QGP
    • Elliptic flow
    • Parton energy loss