Searching for the Quark-Gluon Plasma
in Relativistic Heavy Ion Collisions
Che-Ming Ko
Teaxs A&M University
 Introduction: concepts and definitions
- Quark-gluon plasma (QGP)
- Heavy ion collisions (HIC)
 Experiments and theory
- Signatures of QGP
- Experimental observations
Largely based on slides by Vincenzo Greco
Big Bang
• e. m. decouple (T~ 1 eV , t ~ 3.105 ys)
“thermal freeze-out “
• but matter opaque to e.m. radiation
• Atomic nuclei (T~100 KeV, t ~200s)
“chemical freeze-out”
• Hadronization (T~ 0.2 GeV, t~ 10-2s)
• Quark and gluons
We’ll never see what happened at
t < 3 .105 ys (hidden behind the curtain of
the cosmic microwave background)
Bang
HIC can do it!
Little Bang
N  D  N “Elastic”
finite Dt
Freeze-out
Hadron Gas
Phase Transition
Plasma-phase
Pre-Equilibrium
Heuristic QGP phase transition
Free massless gas
E
g  3
 4 gtot  g g  78 ( g q  g q )

d p p f ( p)  g tot T
3 0
V (2 )
30 g g  16 , gq  gq  Nc N s N f
Bag Model
PH  
EH
V
 B 
C
4R
4
P  0  RH
Pressure exceeds the Bag
pressure -> quark liberation
37  2 904  1/ 4 B1/4 ~ 210 MeV
B B > T ~ 145 MeV
Tc  T 
2 
c
90  37 
1/ 4
Extension to
finite mB , mI
Quantum ChromoDynamics
1
 m
m a 
   ψi γ m  i  gAa ψi  mi ψi ψi   Fam Fam
2
4 a
i 1

nf
Fam   m Aa   Aam  i f abc Abm Ac
Similar to QED, but much richer structure:
 SU(3) gauge symmetry in color space
 Approximate Chiral Symmetry in the light sector
which is broken in the vacuum.
 UA(1) ciral
 Scale Invariance broken by quantum effects
Phase Transition in lattice QCD
Enhancement of the degrees
of freedom towards the QGP
  0.7 GeV / fm
3
Tc  173 15 MeV
Noninteracting massless partons
   qq
 2 7
 4
  g   6n f  16 T
30  4

Gap in the energy density
(Ist order or cross over ?)
QCD phase diagram
From high rB regime
to high T regime
AGS
SPS
RHIC
2
sNN  ( pA  pB )2  ECMS
We do not observe hadronic systems
with T> 170 MeV (Hagedon prediction)
Definitions and concepts
in HIC
Kinematics
Observables
Language of experimentalist
The RHIC Experiments
Au+Au
STAR
Soft and Hard
SOFT (non-pQCD) string fragmentation in e+e , pp … or
(pT<2 GeV)
string melting in AA (AMPT, HIJING, NEXUS…)
QGP
HARD minijets from first NN collisions
Independent Fragmentation : pQCD + phenomenology
• Small momentum transfer
• Bulk particle production
– How ? How many ? How are they
distributed?
• Only phenomenological
descriptions available (pQCD
doesn’t work)
99% of particles
Collision Geometry - “Centrality”
Spectators
Participants
S. Modiuswescki
15 fm
0
b
N_part
For a given b,
Glauber model
0 fm predicts N
part
394 and Nbinary
Kinematical observables
1 E  pz
y  ln
2 E  pz
Additive like Galilean velocity
y j / CM  y j / LAB  yLAB / CM
Transverse mass
mT   m  p
2

2 1/ 2
T
E  mT cosh y , pz  mT sinh y
Angle with respect to beam axis

1  | p |  pz 
   ln tan( / 2)  ln  

2  | p |  pz 
PHOBOS
Rapidity -pseudorapidity
dN
m2
dN
  1 2

2
ddpT
mT cosh y dydpT
PHOBOS
Energy Density
| Dy |  0.5
Energy density a la Bjorken:
dET
1 dET
ε

A T dz πR 2 τ dy
Particle streaming from origin
z
 v z  tanh y
t
 dz   cosh y dy
R  1.18 A  7 fm
τSPS  1 fm/c
Estimate  for RHIC:
dET/dy ~ 720 GeV
Time estimate from hydro:
  0.6 fm/c   ~ 8 GeV/fm
3
1/3
τ RHIC  0.4  1 fm/c
 Tinitial ~ 300-350 MeV
Some definitions I: radial collectiv flows
Slope of transverse momentum spectrum
is due to folding temperature with radial
collective expansion <bT> from pressure.
Absence
1
Non  relativistic p T  m , Tsl  Tf  m v T
2
1  vT
Ultra  relativistic p T >> m, Tsl  Tf
1  vT
2
Slopes for hadrons with different masses
allow to separate thermal motion
from collective flow
Tf ~ (120 ± 10) MeV
<bT> ~ (0.5 ± 0.05)
Collective flow II: Elliptic Flow
Fourier decomposition of particle
momentum distribution in x-y plane
dN
dN 

1  2  v n cos(n )

dpT d dpT 
n
z
y
x
Anisotropic Flow
Measure of the pressure gradient
Good probe of
early pressure
v2 is the 2nd Fourier coeff. of particle
transverse moment distribution
px2  p y2
v2  cos2 
px2  p y2
Anisotropic flow
Anisotropic flow vn

d3N
dN
1
dN 

E 3 

1

2v
(p
,
y)cos(n

)
 n T

d p pT dpT d dy 2 pT dpTdy  n=1

Sine terms vanish because of the symmetry  in A+A collisions

Initial
x spatial
anisotropy
Pressure
gradient
anisotropy
Anisotropic
flows
Statistical Model
Temperature
Yield
Maximum entropy principle
Mass
Chemical Potential
Quantum Numbers
Is there a dynamical evolution that
leads to such values of temp. &
abundances?
Hydro adds radial flow &
freeze-out hypersurface
for describing the
differential spectrum
Yes, but what is Hydro?
HYDRODYNAMICS
Local conservation Laws 5 partial diff. eq. for 6 fields (p,e,n,u)
+ Equation of State p(e,nB)
m
 mT ( x)  0 T m ( x)  e( x)  p( x)u m ( x)u ( x)  p( x) g m
 m
 m jB ( x)  0 jBm ( x)  nB ( x)u m ( x)
 No details about collision dynamics (mean free path >0)
Transport Model
  Follows time evolution of particle distribution
f q , g ( r , p, t )
from initial non-equilibrium partonic phase
 


f p
   r f   rU   p f  I coll
Non-relativistically
t m
drift

2 2
coll
Ip
m
m
f ( fI3
1 2 3
mean field
collision
I
I
4 1 2
2

2
2

3
f 4  f1 f 2 )W1234 ( p1 
coll
coll
coll
gg>ggg
Relativistically
p

p
2... 3  p4 )
g>gg
To be treated:
- Multiparticle collision (elastic and inelastic)
- Quantum transport theory (off-shell effect, … )
- Mean field or condensate dynamics
at High density
Transport
Spectra still appear thermal
Hydro
Elliptic Flow
rapidity
rapidity
• Chemical equilibrium with a limiting Tc ~170MeV
• Thermal equilibrium with collective behavior
- Tth ~120 MeV and <bT>~ 0.5
• Early thermalization ( < 1 fm/c,  ~ 10 GeV/fm3)
- very large v2
We have not just crashed 400 balls to get fireworks,
but we have created a transient state of plasma
A deeper understanding of the system
is certainly needed!
Signatures of quark-gluon plasma
 Dilepton enhancement (Shuryak, 1978)
 Strangeness enhancement (Meuller & Rafelski, 1982)
 J/ψ suppression (Matsui & Satz, 1986)
 Pion interferometry (Pratt; Bertsch, 1986)
 Elliptic flow (Ollitrault, 1992)
 Jet quenching (Gyulassy & Wang, 1992)
 Net baryon and charge fluctuations (Jeon & Koch;
Asakawa, Heinz & Muller, 2000)
 Quark number scaling of hadron elliptic flows (Voloshin
2002)
 ……………
Dilepton spectrum at RHIC
MinBias Au-Au
thermal
• Low mass: thermal dominant
(calculated by Rapp in kinetic model)
• Inter. mass: charm decay
No signals for thermal
dileptons yet
Strangeness Enhancement
Basic Idea:
 Production threshold is lowered in QGP
In the QGP:
qq ss
 QQGP  2ms  250  300 MeV
g  g  s  s
Hadronic channels:
  K  K (Q  2mK  2m  710 MeV )
NN  NK
(Q  m  mK  mN  670 MeV )
N  K
(Q  m  mK  mN  m  530 MeV )
Equilibration timescale? How much time do we have?
QGP Scenario
Hadronic Scenario
Decreasing threshold in
a Resonance Gas
ND  NK (Q  380 MeV )
D  K (Q  240 MeV )
DD  NK (Q  90 MeV )
r   (Q  80 MeV )
To be weighted with
the abundances
npQCD calculation with quasi particle picture
and hard-thermal loop still gives t~5-10 fm/c
How one calculates the Equilibration Time
d3p
Tm2  1  nm 
req  g 
K2 


3 f ( p) 
2

n
T
(2 )
n 1


dr S
 g12  v
dt
r1r2  v
12 SS
72 qq
g12  N N N f  
256 gg
2
c
2
s
r
SS 12
2
S

Similarly in hadronic case
but more channels
Reaction dominated by gg
6 fm/c
 (pQCD) Equilibration time in
QGP teq ~10 fm/c > tQGP
 Hadronic matter teq ~ 30 fm/c
Experimental results
Strangeness enhancement 1
Ej

Y /N

Y / N


j
wound AA
j
wound ref
Strangeness enhancement 2
S 
2 ss
uu  dd
e+e- collisions
Schwinger mechanism
J/Y suppression
In a QGP enviroment:
• Color charge is subject to screening in QGP
> qq interaction is weakened
• Linear string term vanishes in the deconfined phase
(T) > 0 deconfinement
q
V / TC
q
q,q,g distribution modified
Coulomb > Yukawa
V 
 eff
r

 eff
r

e
r
D
rTC
 =0 doesn’t mean no bound !
Screening Effect
• Abelian
• Non Abelian
(gauge boson self-interaction)
 eff (T )
1
H

e
2 mr 2
r
Bound state
dE ( r )
dr
TBound 
0.84
2 eff
One loop pQCD
r
D ( T )
solution
0
m

  2
c  c g (T )
V
4
4 r
D >
 210 MeV
9
150 MeV
 Nc N f 
D   

6 
 3
1.2
 eff m
 1.2 rBohr

1
2
 gT 
1
 2 / 3  gT 
1
  0.3T
latt
D
TBound is not Tc !
In HIC at √s ~ SPS, J/Y should be suppressed !
1
Lattice result for V channel (J/y)
A(w)  w2r (w)
J/y (p  0) disappears
between 1.62Tc and 1.70Tc
cu , cd  D cs  Ds
c u, c d  D
J/Y
Initial production
Dissociation
In the plasma
c s  Ds
Suppression
respect
Recombine
with to
extrapolation
from pp
light quarks
For light quarks rBohr ~ 4 fm >> D , dissociation is more effective
but of course also recombination
Associated suppression of charmonium resonances Y’, cc , …
as a “thermometer”, like spectral
lines for stellar interiors
B quark in similar condition at RHIC as Charmonium at SPS
NUCLEAR ABSORBTION
pre-equilibrium cc formation time and
absorbtion by comoving hadrons
HADRONIC ABSORBTION
rescattering after QGP formation
J / Y  h ( , r ,w,...)  D  D
DYNAMICAL SUPPRESSION
(time scale, g+J/Y > cc,…)
pA (models)
abs ~ 6 mb
Fireball dynamical evolution
Dynamical dissociation
J/y + g
c+c+X
gluon-dissociation,
inefficient for
my≈ 2 mc*
“quasifree” dissoc.
[Grandchamp ’01]
• RHIC central: Ncc≈10-20,
• QCD lattice: J/y’s to ~2Tc
If c-quarks
thermalize:
dNy
d
Regeneration in QGP / at Tc
J/y + g
c+c+X
  y ( Ny  Nyeq )
→
←
[Grandchamp
+Rapp ’03]
Charmonia in URHIC’s
RHIC
• dominated by regeneration
• sensitive to:
mc* , open-charm degeneracy
SPS
Pion interferometry
open: without Coulomb
solid: with Coulomb
STAR
Au+Au @ 130 GeV
STAR Au+Au @ 130 AGeV
C ( q)
 1  exp(  qo2 Ro2  qs2 Rs2  ql2 Rl2 )
 1  exp(  q R )
2
inv
2
inv
Ro/Rs~1 smaller than expected ~1.5
Source radii from hydrodynamic model
Fails to explain the extracted source sizes
Two-Pion Correlation Functions and source radii from AMPT
Lin, Ko & Pal, PRL 89, 152301 (2002)
Au+Au @ 130 AGeV
Need string melting and large parton scattering cross section which may be
due to quasi bound states in QGP and/or multiparton dynamics (gg↔ggg)
Emission Function from AMPT
• Shift in out direction (<xout> > 0)
• Strong positive correlation between out position and emission time
• Large halo due to resonance (ω) decay and explosion
→ non-Gaussian source
Jet quenching
Decrease of mini-jet hadrons (pT> 2 GeV) yield,
because of in medium radiation.
Ok, what is a mini-jet?
why it is quenched ?
High pT Particle Production
High pT (>
~ 2.0 GeV/c) hadron production in pp collisions
Jet: A localized collection of hadrons which
come from a fragmenting parton
hadrons
Parton Distribution Functions
Hard-scattering cross-section
c
a
b
d
hadrons
Fragmentation Function
leading
particle
phad= z pc , z <1 energy needed
to create quarks from vacuum
h
d pp
0
D
d

2
2
h/c

K
dx
dx
f
(
x
,
Q
)
f
(
x
,
Q
)
(
ab

cd
)

a
b a
a
b
b

dyd 2 pT
dtˆ
z c
abcd
“Collinear factorization”
Jet Fragmentation-factorization
, K, p ...
c
b
a
A
B
dN h
dN c

dz
Dch ( z c )

c
2
2

d ph
d pc
c
d
ph= z pc , z <1 energy needed
to create quarks from vacuum
AB= pp (e+e)
a,b,c,d= g,u,d,s….
dN c distribution after pp2collision 2
Parton
   dxa dxb f ( xa , Q ) f ( xb , Q )
2
d pc
c
sˆ dσ
( ab  cd ) δ( sˆ  tˆ  uˆ )
π dtˆ
a
A
b
B
(+ phenomenological kT smearing
due to vacuum radiation)
Dc p ( z )
Dc ( z )
 0.2
p/ < 0.2
B.A. Kniehl et al., NPB 582 (00) 514
High pT Particle Production in A+A
h
AB
dN
2
2

ABK
dx
dx
d
k
d
kb

a
b
a

2
abcd
dyd pT
 f a / A ( xa , Q 2 ) f b / B ( xb , Q 2 )
 g (k a ) g (k b )
0
h/c
*
c
2
c
zc*  zc /(1   )
Parton Distribution Functions
Intrinsic kT , Cronin Effect
 S A ( xa , Qa2 ) S B ( xb , Qb2 )
d

(ab  cd )
dtˆ
1
zc*
 0 dP( )
zc
pc*  pc (1   )
Shadowing, EMC Effect
Hard-scattering cross-section
c
Partonic Energy Loss
D (z ,Q )
Fragmentation Function

zc
a
b
d
hadrons
leading particle
suppressed
Energy Loss
~ Brehmstralung radiation in QED
Color makes a difference
k
pi
pi
pf
×
×
pi
pf
a
×
pf
c
k
Gluon multiple scattering
Static scattering centers assumed
thickness

dE
dx
  s N c qˆ L  DE  qˆL2
Non-Abelian gauge
Transport coefficient
qˆ 
q
2


2
m Debye

x 1 w
t form  
 lcoh
v k k
N
scatt
coh
 lcoh /  > 1
Medium Induced Radiation
c
M 2,1,1
Clearly similar Recursion Method is needed
to go toward a large number of scatterings!
Ivan Vitev, LANL
Jet Quenching
L/ opacity
Large radiative energy loss
in a QGP medium
DE/E ~ 0.5
Jet distribution
Non – abelian energy loss
DE ( 0 ) 3α μL  2 E 

log  2 
E
4 g
μ L
DE  E  weak pT dependence
of quenching
Quenching
Energy Loss and expanding QGP
qL 
2
eff
 2E 

  d  r ( , ) ln 
2 
m
(

)




r ( )  r0  / 0 
 out
0
Probe the density
m ( )  gT ( )  g r ( ) / 2
In the transverse plane
Quenching is angle dependent

dN
dN 

1  2  v n cos(n )

dpT d dpT 
n
px2  p y2
v2  cos2 
px2  p y2
1/ 3
How to measure the quenching
Self-Analyzing (High pT) Probes of the Matter at RHIC
Nuclear
Modification
Factor:
d 2 N AA / dpT d
RAA ( pT ) 
Ncoll d 2 N NN / dpT d
nucleon-nucleon
cross section
<Ncoll>
AA
If R = 1 here, nothing new
going on
Centrality Dependence
Au + Au Experiment
d + Au Control
• Dramatically different and opposite centrality evolution of
Au+Au experiment from d+Au control.
• Jet suppression is clearly a final state effect.
Is the plasma a QCD-QGP?
 Consistent with L2 non-abelian plasma behavior
 Consistent with  ~ 10 GeV (similar to hydro)
Baryon-Meson Puzzle
pions
protons
PHENIX,nucl-ex/0212014
PHENIX, nucl-ex/0304022
0 suppression: evidence of jet
quenching before fragmentation
 Fragmentation p/ ~ 0.10.2
 Jet quenching should affect both
Fragmentation is not the dominant
mechanism of hadronization at
pT ~ 1-5 GeV !?
Coalescence vs. Fragmentation
Parton spectrum
Fragmentation:
 Leading parton pT
ph= z pT
according to a probability Dh(z)
 z < 1, energy needed to create quarks
from vacuum
Coalescence:
BM
 partons are already there
$ to be close in phase space $
 ph= n pT ,, n = 2 , 3
baryons from lower momenta

Even if eventually
Fragm. takes over …
p  p 
C ( pT )   T   T 
 2   2 
p 
F ( pT )   T 
 z 


C  4
 
F   z  pT




Coalescence
dNm
2
3
3
 VF  d p1d p2 f q ( p1 ) f q ( p2 ) Μ( qq  m)
3
d P
Our implementation
M qq  m
2
npQCD
1 dNq
f q ( p) 
VF d 3 p
  
2
  
3
W  
(3)
  p1 , p2 | P, m  g m  d r f m (r , q ) δ ( P  p1  p2 )
9π
f  D2x  ( x1  x2 )2  D2p  ( p1  p2 )2  (m1  m2 ) 2 
2
D x  1/ D p coal. parameter
|Mqq->m|2 depends only on the
g m spin  color probabilit y
phase space weighted by wave
function (npQCD also encoded
 Energy not conserved
in the quark masses , mq=0.3
 No confinement constraint
GeV, ms=0.475 GeV)
W
m
Coalescence Formula
n


d 3 pi
dN H

    pi dσ i
f ( xi , pi )  f H ( x1 ... xn , p1... pn )δ( pT  piT )
2
3 q
d pT
( 2π )
i 1 

fq invariant parton distribution function
thermal (mq=0.3 GeV, ms=0.47 GeV)
with radial flow b0.5)
+
quenched minijets (L/3.5
fH hadron Wigner function
fM 

 
9π
2
2
2
2
2

D

(
x

x
)

D

(
p

p
)

(
m

m
)
x
1
2
p
1
2
1
2
2(D x D p )3
Dx = 1/Dp coalescence radius


 2
( p1  p2 ) In the rest frame
Distribution Function
T=170 MeV
| Dy |  0.5
soft
ET ~ 700 GeV
b(r) ~ 0.5 r/R
T ~ 170 MeV
hard
L/3.5
P. Levai et al., NPA698(02)631
V ~ 900 fm-3
 ~ 0.8 GeV fm-3)
Hadron from coalescence may
have jet structure (away suppr.)
REALITY: one spectrum with correlation kept also at pT < 2 GeV
Pion & Proton spectra
Au+Au @200AGeV (central)
ρ  ππ
V. Greco et al., PRL90 (03)202302
PRC68(03) 034904
R. Fries et al., PRL90(03)202303
PRC68(03)44902
R. C. Hwa et al., PRC66(02)025205
 Proton enhancement
due to coalescence!
Baryon/Meson ratio
Be careful , there are mass effects !
 Resonance decays r >  
 Shrinking of baryon phase
space
p
Fragmentation not included for 
Momentum-space coalescence model
Including 4th order quark flow Kolb, Chen, Greco, & Ko, PRC 69 (2004) 051901
f q (pT )  1  2v 2,q (pT )cos(2 )  2v 4,q (p T )cos(4 )
Meson flow
v 2,M =
2v 2,q + 2v 2,q v 4,q
1 + 2(v
2
2,q
2
4,q
+v )
, v 4,M =
2v 4,q + v 22,q
1 + 2( v 22,q + v 24,q )
Baryon flow
v 2,B =
3v 2,q + 6v 2,q v 4,q + 3v 32,q + 6v 2,q v 24,q
2
2,q
2
4,q
2
2,q 4,q
1 + 6( v + v + v v )
, v 4,B =
3v 4,q + 3v 22,q + 6v 22,q v 4,q + 3v 34,q
1 + 6(v 22,q + v 24,q + v 22,q v 4,q )
v 4,M 1 1 v 4,q v 4,B 1 1 v 4,q
⇒ 2 = + 2 , 2 = + 2
v 2,M 4 2 v 2,q v 2,B 3 3 v 2,q
Elliptic Flow from Coalescence
Enhancement
partonic v2
Coalescenceofscaling
v 2,M (p1T ) 2v
pT2,q (p T /2)
V2  
v 2,B (pnT ) 3vn2,q (p T /3)
Wave function effects
> scaling breaking 10% q/m
5% b/m
wave function effect
Effect of Resonances on Elliptic Flow
Pions from resonances
w.f. + resonance decay
K&p
*
K, , moved
p … v2 not
affected
 coal.
towards
 data
by resonances!
nucl-th/0402020
Higher-order anisotropic flows
Data can be described by
a multiphase transport
(AMPT) model
Parton cascade
v4,q  v22,q
v4
2

1.2
⇒
v

2v
Data
4,q
2,q in naive quark coalescenc e model
2
v2
Back-to-Back Correlation
trigger
Assoc.
quenched
Trigger is a particle at
4 GeV < pTrig < 6 GeV
Associated is a particle at
2 GeV < pT < pTrig
Away Side: quenching
has di-jet structure
Same Side: Indep. Fragm.
equal (?!) to pp
Coalescence from s-h leads to away side suppression,
While same side is reduced if no further correlation …
Unexpected: Appreciable charm flow
Does Charm quark thermalize?
 v2 of D meson (single e)
coalescence/fragmentation?
energy loss?
 pT Spectra and Yield of J/Y
From hard pp collision
D meson spectra
V. Greco , PLB595 (04) 202
S. Batsouli,PLB557 (03) 26
D mesons
D mesons
B mesons
No B mes.
Single electron does not
resolve the two scenarios
Elliptic flow better probe of interaction
Charmed Elliptic Flow
Flow mass effect
V2q from , p, , 
Coalescence can predict
v2D for v2c = 0
&
v2c = v2q
V2 of electrons
S. Kelly,QM04
Quenching
VGCMKRR, PLB595 (04) 202
Quark gluon plasma was predicted to be a weakly
interacting gas of quarks and gluons
The matter created is not a firework of multiple minijets
 Strong Collective phenomena
Hydrodynamics describes well the bulk of the matter
Transport codes needs a quite large npQCD cross section
Charm quark interacts strongly in the plasma
Recent lattice QCD finds bound states of cc at T>Tc
Rethinking the QGP at Tc < T < 2Tc
“Strong” QGP
Summary
 Most proposed QGP signatures are observed at RHIC.
 Strangeness production is enhanced and is consistent with
formation of hadronic matter at Tc.
 Large elliptic flow requires large parton cross sections in transport
model or earlier equilibration in hydrodynamic model.
 HBT correlation is consistent with formation of strongly interacting
partonic matter.
 Jet quenching due to radiation requires initial matter with energy density
order of magnitude higher than that of QCD at Tc.
 Quark number scaling of elliptic flow of identified hadrons is consistent
with hadronization via quark coalescence or recombination.
 Studies are needed for electromagnetic probes and heavy flavor hadrons.
 Theoretical models have played and will continue to play essential roles
in understanding RHIC physics.
Conclusions
Matter with energy density too high for simple hadronic
phase (  > c from lattice)
Matter is approximately thermalized (T >Tc )
Jet quenching consistent with a hot and dense medium
described by the hydrodymic approach
Hadrons seem to have typical features of recombination
Strangeness enhancement consistent with grand canonical
ensemble
J/y ...
Needed : - Thermal spectrum
- Dilepton enhancement
A Lot of work to do …
Lattice QCD
Effective field theory
Transport theory (quantum, field condensate,…)
pQCD
Understanding of Non-Abelian Interaction !
Scientific approach to an important part
of the evolution of the primordial plasma
can be achieved