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 of 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 »

QCD Interactions Weaken at High Energy (S. Bethke, hep-ex/0211012)

The qu quark-gluon plasma Energy density Free gas limit Temperature (from F. Karsch, hep-lat/0106019)

Weak coupling calculations provide adequate Weak coupling calculations provide adequate description escription Of Of the thermodynamics at high temperature the thermodynamics at high temperature ( T � 3 T c ) Dimensional reduction Weakly interacting Weakly interacting quasiparticles quasiparticles SU(3) Pressure (from F. Karsch, hep-lat/0106019) (from F. Kajantie et al, PRL86, PRD67)

Effective Effective coupling oupling in 3d n 3d reduced theory educed theory (relevant (relevant scale is cale is 2 π T)

The QCD phase diagram T Quark-Gluon Plasma Hadronic matter Colour superconductor Nuclei µ B

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 of 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 2 � g 2 A 4 � g 2 A 2 2 ( ) � A

Gluon saturation (Gribov, Levin, Ryskin 83) Large gluon densites at small x A 2 � xG ( x , Q 2 ) � R 2 2 � g 2 A 2 2 ( ) � A Non linear effects important when Q 2 � g 2 A 2 i.e. at a characterisitic scale xG ( x , Q 2 ) 2 � � s Saturation scale Saturation scale Q s � R 2 k T � Q s k T � Q s (saturated regime) (dilute regime)

The The saturation aturation scale cale From From fit to DIS (HERA) it to DIS (HERA) � � � 2 x 0 2 ( x ) = Q 0 Q s � � � x � In a nucleus In a nucleus 2 � Q 0 2 A 1/ 3 Q 0 The densities in the central rapidity of a nucleus-nucleus collision at RHIC are similar to those at HERA. At the LHC At RHIC, smaller x can be reached in the forward rapidity region

Early stages of a nucleus-nucleus collision Partons set free have typical tranverse momenta Partons set free have ypical tranverse momenta k T � Q s � 1 � � Q s They They are set free re set free at t (proper roper) time time At that At that time ime dE T dN dy � 2 Q s AxG ( x , Q s ) dy � 2 AxG ( x , Q s ) 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 xG ( x , Q 2 ) 2 � � s Q s � R 2 Large occupation arge occupation numbers numbers n � xG ( x , Q 2 ) � 2 n � � 2/ Q s � R 2 Q s � s Classical fields Classical ields McLerran-Venugopalan, etc. 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 s � 5 � A � GeV AGS/BNL SPS/CERN RHIC/BNL s � 200 � A � Gev LHC/CERN s � 5000 � A � Gev

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 ocus 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 1 dE T � Bj ( � 0 ) = � R 2 � 0 dy � Bj (1 fm / c ) � 5.5 GeV / fm 3 � Bj (0.35 fm / c ) � 16 GeV / fm 3 ( � 0 � 1/ m T ) � Bj (0.14 fm / c ) � 40 GeV / fm 3 ( � 0 � 1/ Q s )

Elliptic flow

Produced particles flow preferentially in the reaction plane (J.-Y. Ollitrault, 1992) y 2 � x 2 � x = y 2 + x 2 V 2 = cos(2 � ) (S. Voloshin and Y. Zhang, 1994) (P.F. Kolb, J. Sollfrank and U. Heinz, PRC 62 (2000) 054909)

Elliptic flow (Phenix white paper)

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

Strong Strong conclusions onclusions drawn from comparison rawn from comparison with hydrodynamical calculations with hydrodynamical calculations: - early arly thermalisation time hermalisation time - sensitivity ensitivity to o equation quation of state f state - - low viscosity ow viscosity

R.S. Bhalerao, J.-P. B, N. Borghini, J.-Y. Ollitrault, nucl-th/0508009 Good control parameter ? -initial -initial energy density nergy density (no) no) � � � � c s R dN � -average number -average number of collisions f collisions during uring � � c S dy � � the build the build up of p of elliptic flow lliptic flow (?) ?) (From NA49, nucl-ex/0303001)

Jet quenching and strong « final state » interactions

Jet production in matter Au-Au nucl-ex/0304022 q q / Yield N � � AuAu binary AuAu R = AA Yield pp

Control experiment: d-AU (PHENIX, nucl-ex/0401001)

QM’05

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

Hints of gluon saturation

Suppression Suppression can also be can also be due to initial ue to initial state effects state ffects (nuclear wave function uclear wave function probed at small x; color probed at small color glass lass condensate condensate) y 0 0.05 0.1 0.2 0.4 0.6 1 1.4 2 Solution of the BK equation, Albacete et al, hep-ph/0307179 (Related analytical work by Iancu, Itakura, Triantafyllopoulos hep-ph/0403103)

(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 ollision dynamics at dynamics at RHIC HIC - Early arly stages of tages of the the collisions, ollisions, 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 ore so at o at LHC). HC). - Hints ints of saturation ( f saturation (color olor glass lass condensate ondensate) 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