Galileo Galilei Institute Inaugural Conference September 20, 2005 - - PowerPoint PPT Presentation

The search for the Quark-Gluon Plasma Theoretical and experimental status

Galileo Galilei Institute Inaugural Conference

September 20, 2005

Jean-Paul Blaizot, CNRS and ECT*

Fundamental Fundamental questions uestions

• What is the form of
• f matter at « extreme »

temperature or de density?

• What is the wave function of a hadron, a

nucleus, at asymptotically high energy? SIMPLICITY emerges in extreme (asymptotic) ) situations

At high temperature and/or high density matter is « simple »

(S. Bethke, hep-ex/0211012)

QCD Interactions Weaken at High Energy

The qu quark-gluon plasma

(from F. Karsch, hep-lat/0106019)

Energy density Temperature Free gas limit

(from F. Kajantie et al, PRL86, PRD67) (from F. Karsch, hep-lat/0106019)

Weakly interacting Weakly interacting quasiparticles quasiparticles Weak coupling calculations provide adequate Weak coupling calculations provide adequate description escription Of Of the thermodynamics at high temperature the thermodynamics at high temperature SU(3) Pressure Dimensional reduction

(T 3Tc)

Effective Effective coupling

• upling in 3d

n 3d reduced theory educed theory (relevant (relevant scale is cale is 2πT)

T

µB

Hadronic matter Quark-Gluon Plasma

Nuclei

Colour superconductor

The QCD phase diagram

Theory n near T Tc i is d difficult

Degrees of freedom? Strong coupling? Bound states?

… and p present e experiments m may b be Probing t this r region…

How does the wavefunction of a nucleus look like at asymptotically high energy ?

High density partonic systems

Parton Parton density grows ensity grows as x s x decreases decreases

Relevant in the very early stages

• f nucleus-nucleus collisions

Physics Physics of dense f dense systems systems of quarks f quarks and and gluons luons

Weak coupling but many active degrees of freedom Non linear QCD effects become important when

A

( )

2 g2 A4 g2 A2 2

Gluon saturation

Saturation Saturation scale scale

Non linear effects important when

(Gribov, Levin, Ryskin 83)

Large gluon densites at small x i.e. at a characterisitic scale

A

( )

2 g2 A2 2

A2 xG(x,Q2) R2

Q2 g2 A2

Qs

2 s

xG(x,Q2) R2

kT Qs

kT Qs

(saturated regime) (dilute regime)

The The saturation aturation scale cale

In a nucleus In a nucleus The densities in the central rapidity of a nucleus-nucleus collision at RHIC are similar to those at HERA. From From fit to DIS (HERA) it to DIS (HERA) At the LHC At RHIC, smaller x can be reached in the forward rapidity region

Qs

2(x) = Q0 2 x0

x

• Q0

2 Q0 2A1/ 3

Early stages of a nucleus-nucleus collision

Partons set free have Partons set free have typical tranverse momenta ypical tranverse momenta They They are set free re set free at t (proper roper) time time At that At that time ime

kT Qs

Qs

1

dN dy 2AxG(x,Qs)

dET dy 2QsAxG(x,Qs)

Phenomenology based Phenomenology based on n such uch arguments ( rguments (refined efined) is reasonably successful at is reasonably successful at RHIC HIC

High density partonic systems

Large occupation

arge occupation numbers numbers Classical Classical fields ields McLerran-Venugopalan, etc.

Qs

2 s

xG(x,Q2) R2 n xG(x,Q2) R2

• Qs

2 n

s

2/Qs

Non Non linear evolution equations linear evolution equations Balitsky-Kovchegov equation

COLOR GLASS CONDENSATE and JIMWLK(*) equation

(*) Jalilian-Marian, Iancu, McLerran, Weigert, Leonidov, Kovner

Hot and dense matter is produced in ultra-relativistic heavy ion collisions

SPS/CERN RHIC/BNL

s 200 A Gev

LHC/CERN

s 5000 A Gev s 5A GeV

AGS/BNL

RHIC experiments

Some important results from RHIC

Large energy density achieved Collective behaviour observed Jet quenching and strong « final state » interactions Hints of gluon saturation

And much And much, much uch, more! more!…

(Focus

• cus on observables sensitive to initial state)

n observables sensitive to initial state)

Large energy density

Moderate increase of multiplicity with beam energy

From Phenix White paper

Bjorken energy density Bjorken energy density

Bj(1fm /c) 5.5GeV / fm3 Bj(0.35 fm /c) 16GeV / fm3 Bj(0.14 fm /c) 40GeV / fm3

Bj( 0) = 1 R2 0 dET dy

( 0 1/mT ) ( 0 1/Qs)

Elliptic flow

Produced particles flow preferentially in the reaction plane

(J.-Y. Ollitrault, 1992)

x = y 2 x 2 y 2 + x 2

(P.F. Kolb, J. Sollfrank and U. Heinz, PRC 62 (2000) 054909)

V2 = cos(2)

(S. Voloshin and Y. Zhang, 1994)

Elliptic flow

(Phenix white paper)

Comparison with hydrodynamics

(From U. Heinz, nucl-th/0412094)

Strong Strong conclusions

• nclusions drawn from comparison

rawn from comparison with hydrodynamical calculations with hydrodynamical calculations:

• early

arly thermalisation time hermalisation time

• sensitivity

ensitivity to

• equation

quation of state f state

• low viscosity
• w viscosity

Good control parameter ?

• initial
• initial energy density

nergy density (no) no)

• average number
• average number of collisions

f collisions during uring the build the build up of p of elliptic flow lliptic flow (?) ?)

R cs c

• S

dN dy

• (From NA49, nucl-ex/0303001)

R.S. Bhalerao, J.-P. B, N. Borghini, J.-Y. Ollitrault, nucl-th/0508009

Jet quenching and strong « final state » interactions

q q

pp AuAu binary AuAu AA

Yield N Yield R

/

• =

Au-Au nucl-ex/0304022

Jet production in matter

(PHENIX, nucl-ex/0401001)

Control experiment: d-AU

QM’05

STAR: Phys.Rev.Lett.91:072304,2003

Hints of gluon saturation

Solution of the BK equation, Albacete et al, hep-ph/0307179

y

0.05 0.1 0.2 0.4 0.6 1 1.4 2

(Related analytical work by Iancu, Itakura, Triantafyllopoulos hep-ph/0403103)

Suppression Suppression can also be can also be due to initial ue to initial state state effects ffects (nuclear wave function uclear wave function probed at small probed at small x; color color glass lass condensate condensate)

(Kharzeev, Kovchegov, Tuchin, hep-ph/0405045)

SUMMARY

• Strongly interacting matter is produced
• Strongly interacting matter is produced in high energy

high energy nucleus-nucleus collisions. Large « nucleus-nucleus collisions. Large « initial nitial » energy density nergy density. Collective Collective behaviour ehaviour.

• Many

any (indirect) indirect) evidences that partonic degrees evidences that partonic degrees of freedom freedom play play an important n important role role in the the collision

• llision dynamics at

dynamics at RHIC HIC

• Early

arly stages of tages of the the collisions,

• llisions, and hence

and hence « initial state nitial state effects effects » are important are important at at RHIC ( HIC (and will be nd will be more

• re so at
• at LHC).

HC).

• Hints

ints of saturation ( f saturation (color

• lor glass

lass condensate

• ndensate) may be already

ay be already present at present at RHIC.

• HIC. Phenomenology based

henomenology based on saturation n saturation ideas is deas is reasonably successful at reasonably successful at RHIC HIC