Kharzeev

QCD and Heavy Ions:an overview: 

QCD and Heavy Ions: an overview D. Kharzeev BNL XXXIX Rencontres de Moriond, March 28 - April 4 2004

Outline: 

Outline QCD of strong color fields: parton saturation and Color Glass Condensate Manifestations of CGC at RHIC: hadron multiplicities high pT suppression at forward rapidity Future tests: RHIC, LHC, eRHIC From CGC to Quark-Gluon Plasma

QCD and the classical limit: 

QCD and the classical limit QCD = Quark Model + Gauge Invariance For , .i Classical dynamics applies when the action is large: => Need weak coupling and strong fields

Asymptotic freedom and the classical limit of QCD: 

Asymptotic freedom and the classical limit of QCD Classical limit S>>1 requires weak coupling and strong fields; Large distances: strong fields but large coupling… Is there a place for classical methods?

Parton saturation and the classical limit of QCD: 

Parton saturation and the classical limit of QCD At small Bjorken x, hard processes develop over .large longitudinal distances All partons contribute coherently => at sufficiently small x and/or .large A strong fields, weak coupling!

The phase diagram of high energy QCD: 

The phase diagram of high energy QCD … no numbers yet, but they will follow

Non-linear effects in the QCD evolution: 

Non-linear effects in the QCD evolution QCD evolution equations (DGLAP, BFKL) predict an increase of parton densities at small Bjorken x, in agreement with experiment; at “sufficiently small” x and/or large A non-linear effects must become important (GLR; MQ; JIMWLK; ILM). At large , equations can be written in a closed form - BK (dipole scatterings are assumed to be independent - similar to the mean field approximation in statistical physics) but correlations may be important - see e.g. E.Iancu, A.H.Mueller, hep-ph/0309276; A.H.Mueller, A.I.Shoshi, hep-ph/0402193

CGC and total multiplicities in Au-Au: 

CGC and total multiplicities in Au-Au CGC predicts very simple dependence of multiplicity .on atomic number A / Npart: Almost like in “wounded nucleon” and string-based models; Agrees unexpectedly well with “soft + hard” parameterizations (note: total multiplicities are dominated by small transverse momenta => classical dynamics applicable)

Slide9: 

dNch/dh @ h=0 vs Energy Parton interactions at RHIC .are coherent !

Centrality dependence of hadron multiplicity: 

Centrality dependence of hadron multiplicity => Talk by D. Hofman

Centrality dependence at different energies: 

Centrality dependence at different energies

Initial state parton saturation? : 

Initial state parton saturation? QM2002: nucl-ex/0212009 l~0.25 from fits to HERA data: xG(x)~x-l Describes energy dependence correctly! Kharzeev, Levin, Nardi, hep-ph/0111315 200 GeV 130 GeV Preliminary 19.6 GeV

Slide13: 

Parton Saturation Describes Au + Au Kharzeev & Levin, Phys. Lett. B523 (2001) 79 Au + Au at 130 GeV We need a simpler system such as d + Au in order to understand a complex system Au + Au The results of d+Au are crucial for testing the saturation approach PHOBOS Coll., R. Noucier Color Glass Condensate describes the Au-Au data

D-Au multiplicities: 

D-Au multiplicities Data from BRAHMS and PHOBOS Collaborations DK, E.Levin and M.Nardi, Nucl.Phys.A730(2004)448, + erratum, hep-ph/0212316

From CGC to Quark Gluon Plasma:approach to thermalization: 

From CGC to Quark Gluon Plasma: approach to thermalization The data on azimuthal anisotropy of hadron production indicate strong final state interactions at short time scales U.Heinz, E.Shuryak, … => Talk by R.Snellings Problem: if interactions are perturbative, interaction probabilities are small - suppressed by powers of if interactions are non-perturbative, characteristic re-interaction time is about 1 fm Possible solution: CGC sets a fast time scale (~ 0.2 fm) and classical fields re-interact with ~ O(1) probability (almost) isentropic evolution => ideal hydrodynamics is reasonable R.Baier, A.H.Mueller, D. Schiff, D.T. Son, PLB502(2001)51; 539(2002)46; …

From CGC to Quark Gluon Plasma: 

From CGC to Quark Gluon Plasma L. McLerran, T. Ludlam, Physics Today, October 2003

Signatures of the Quark Gluon Plasma: 

Signatures of the Quark Gluon Plasma O jet quenching suppression of heavy quarkonia collective flow fluctuations and correlations dilepton and photon enhancement particle abundancies exotica: DCC, parity violation, …

The discovery of high pT suppression at RHIC: 

The discovery of high pT suppression at RHIC => Talk by D. d’Enterria

What happens at higher transverse momenta?: 

What happens at higher transverse momenta? PHENIX and STAR extend measurements to ~ 10 GeV

Centrality Dependence vs pT: 

Centrality Dependence vs pT Phobos Phobos

Is this the jet quenching in QGP?: 

Is this the jet quenching in QGP? Bjorken; Gyulassy, Wang; Baier, Dokshitzer, Mueller, Peigne, Schiff; Wiedemann, Salgado; Vitev, Levai, … Very likely; .but could there be alternative explanations? (2002)lternative DK, Levin, McLerran hep-ph/0210332 Yes, possibly: 1) Small x evolution leads to .the modification of gluon propagators - “anomalous dimension”: 2) Qs is the only relevant dimensionful parameter in the CGC; .thus everything scales in the ratio 3) Since Tthe A-dependence is changed => Npart scaling!

D-Au collisions: suppression or enhancement? : 

D-Au collisions: suppression or enhancement?

RdAu vs pT: 

RdAu vs pT Central Au+Au Phobos

p+p vs. d+Au: 

p+p vs. d+Au Azimuthal correlations are qualitatively consistent Quantitative evaluation will constrain Nuclear kT from initial state multiple scattering Shadowing Models that predict “monojets” due to initial state effects ruled out No “data manipulation” D. Hardtke, STAR Coll. => Talk by F. Wang

Conclusion:high pT suppression is a final-state effect: 

Conclusion: high pT suppression is a final-state effect Can one prove that it is due to a radiative jet energy loss In the Quark-Gluon Plasma? Quite likely: one possibility is to use the heavy quarks Radiation off heavy quarks is suppressed (“dead cone”) => less quenching On the other hand, D mesons have about the same size as .pions and kaons, and so in the hadron absorption scenario .the suppression should be the same Yu.Dokshitzer, DK ‘01 => Talk by N. Armesto

However, the arguments for the CGC-caused,suppression should hold for sufficiently small x;: 

However, the arguments for the CGC-caused ,suppression should hold for sufficiently small x; Does this happen at RHIC? Study the forward rapidity region: Moving to y=+4 from y=0 increases the saturation scale .by factor of three RHIC results: Talks by B. Cole, E. Kistenev, M. Liu, F. Wang

Expectations for RdAu at large rapidity: 

Expectations for RdAu at large rapidity Agreement on the presence of suppression due to the quantum Small x evolution in the CGC picture: DK, E. Levin and L. McLerran, hep-ph/0210332; R. Baier, A. Kovner, U. Wiedemann, hep-ph/0305265 v2 DK, Yu.Kovchegov and K. Tuchin, hep-ph/0307037 v2 J. Albacete, N. Armesto, A. Kovner, C. Salgado, U. Wiedemann, hep-ph/0307179; Agreement on the presence of Cronin effect in the classical ,approach and in the multiple scattering picture: L.McLerran and R.Venugopalan; Yu.Kovchegov and A.H.Mueller; J. Jalilian-Marian; A. Dumitru; F. Gelis;… X.N.Wang; M. Gyulassy; I. Vitev;…

Model predictions: 

Model predictions I. Vitev nucl-th/0302002 v2 D. Kharzeev, Yu. Kovchegov and K. Tuchin, hep-ph/0307037 CGC at y=0 Y=0 Y=3 Y=-3 Very high energy As y grows R. Debbe, BRAHMS Coll., Talk at DNP Meeting, Tucson, November 2003

d-Au Nuclear Modification factor at  ~3.2: 

d-Au Nuclear Modification factor at  ~3.2 BRAHMS preliminary RdAu compares the yield of negative particles produced in dAu to the scaled number of particles with same sign in p-p The scale is the number of binary collisions: Ncoll=7.2 (minimum biased) PRL 91 072305 (2003) R. Debbe, BRAHMS Collaboration, Talk at the DNP Meeting, Tucson, November 2003

RdAu at different rapidities: 

RdAu at different rapidities All ratios extracted from minimum biased data samples Number of binary collisions in minimum biased events is estimated: Ncoll = 7.2±0.3 Statistical errors dominant over the systematic ones at =2 and 3 Systematic error (not shown) ~15% The values for =0 were published in: PRL 91 072305 (2003) R.Debbe, BRAHMS, QM’04

Centrality dependence: 

Centrality dependence All numerators and denominator are scaled by the appropriate estimated number of binary collisions (HIJING + BRAHMS GEANT) The ratios are corrected for trigger inefficiency. All other corrections (acceptance, tracking efficiency.. ) cancel out. R.Debbe, BRAHMS, QM’04

Centrality Dependence of Particle Production @Fwd/Bwd Directions: 

Centrality Dependence of Particle Production @Fwd/Bwd Directions Stopped hadrons Mesons + Baryons Light mesons Pions + Kaons Heavy flavors Charm + Beauty Ming Liu, PHENIX, QM’04 => Talk by M. Liu

d+Au RCP at forward rapidities: 

d+Au RCP at forward rapidities PT [GeV/c] RCP Au-Side RCP shows almost no variation with centrality d-side is interesting: more central is more suppressed L.Barnby, STAR, QM’04

d Au spectra at (not so) forward rapidity: 

d Au spectra at (not so) forward rapidity P. Steinberg, PHOBOS, QM’04

Rapidity dependence of RdAu: 

Rapidity dependence of RdAu

Is this “just shadowing”?: 

Is this “just shadowing”? Yes, it is - shadowing is the deviation of nuclear parton distributions from the nucleon’s ones. CGC is a theory of shadowing Conventional parameterizations of shadowing have so far failed in describing the rapidity and centrality dependence of the data (EKS, de Florian, Accardi-Gyulassy,… Some approaches (e.g. HIJING shadowing) describe suppression at y=3, but also predict it at y=0. NB:approaches relating shadowing to diffraction should work

Further tests of quantum evolution in the CGC : 

Further tests of quantum evolution in the CGC Back-to-back correlations for jets separated by several units of rapidity are very sensitive to the evolution effects A.H.Mueller,H.Navelet and to the presence of CGC DK, E.Levin,L.McLerran, hep-ph/0403271 Open charm, dileptons, photons DK, K.Tuchin, hep-ph/0310.. in the forward region R.Baier,A.H.Mueller,D.Schiff, hep-ph/0403201

Phase diagram of high energy QCD : 

Phase diagram of high energy QCD

Summary: 

Summary High energy heavy ion program allows to study QCD in the domains of high parton density (small x, large A) and high energy density Novel exciting effects have been observed in Au-Au and forward d-Au interactions; they point towards the collective partonic behavior and non-linear dynamics at small x

Back-up slides: 

Back-up slides

Slide41: 

d Au Phenix Preliminary Stopped Hadrons!

Slide42: 

d Au Stopped Hadrons! Phenix Preliminary

Slide43: 

d Au Shadowing? Cronin effect & anti-shadowing? Stopped Hadrons! Phenix Preliminary

RCP(y): Muons from Light Meson Decays: 

RCP(y): Muons from Light Meson Decays Phenix Preliminary RCP