Energy and  B dependence in heavy ion collisions D. Kharzeev BNL “From high  B to high energy”, BNL, June 5, 2006

Outline Global observables Baryon transport QCD phase diagram and the tricritical point o hadron multiplicities o elliptic flow o identified hadrons

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

The phase diagram of high energy QCD

Phase diagram of high energy QCD

Asymptotic Freedom At short distances, the strong force becomes weak (anti-screening) - one can access the “asymptotically free” regime in hard processes and in super-dense matter (inter-particle distances ~ 1/T) number of colors number of flavors

Asymptotic freedom and Landau levels of 2D parton gasB The effective potential: sum over 2D Landau levels 1. The lowest level n=0 of radius is unstable! 2. Strong fields Short distances Paramagnetic response of the vacuum: H V

QCD and the classical limit.i Classical dynamics applies when the action is large in units of the Planck constant (Bohr-Sommerfeld quantization) => Need weak coupling and strong fields weak field strong field (equivalent to setting )

Building up strong color fields: small x (high energy) and large A (heavy nuclei) Bjorken x : the fraction of hadron’s momentum carried by a parton; high energies s open access to small x = Q 2 /s Because the probability to emit an extra gluon is ~  s ln(1/x) ~ 1, the number of gluons at small x grows; the transverse area is limited transverse density becomes large GLR; McLerran, Venugopalan Large x the boundary of non-linear regime: partons of size 1/Q > 1/Q s overlap small x

Hadron multiplicities: the effect of parton coherence

Semi-classical QCD and total multiplicities in heavy ion collisions Expect very simple dependence of multiplicity.on atomic number A / N part : N part : Almost the wounded nucleon model!

Classical QCD in action

Classical QCD dynamics in action The data on hadron multiplicities in Au-Au and d-Au collisions support the quasi-classical picture Kharzeev & Levin, Phys. Lett. B523 (2001) 79

Classical QCD in action The data on hadron multiplicities in Au-Au and d-Au collisions support the semi-classical picture KLN

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

Predictions for the LHC KLN, hep-ph/ talk by A.Stasto

How dense is the produced matter? The initial energy density achieved: mean transverse momentum of produced gluons gluon formation time the density of the gluons in the transverse plane and in rapidity about 100 times nuclear density !

What happens at such energy densities? Phase transitions: deconfinement Chiral symmetry restoration U A (1) restoration Data from lattice QCD simulations F. Karsch et al critical temperature ~ K; cf temperature inside the Sun ~ 10 7 K

A.Nakamura and S.Sakai, hep-lat/ Perfect fluid Viscosity of sQGP KSS bound: strongly coupled SUSY QCD = classical supergravity

Viscosity of Quark-Gluon Plasma Au-Au collisions at RHIC produce strongly interacting matter shear viscosity - to - entropy ratio hydrodynamics: QCD liquid is more fluid than water => Small entropy production Hydro limit STAR PHOBOS Hydro limit STAR PHOBOS

How small is really the viscosity? CGC initial conditions lead to larger ellipticity, require some viscous effects: T.Hirano, U.Heinz, DK, R.Lacey, Y. Nara, hep-ph/

How small is really the viscosity? KLN initial conditions lead to larger ellipticity, this is not an artifact of a particular model for the gluon distribution, but a generic feature of saturation T.Hirano, U.Heinz, DK, R.Lacey, Y. Nara, hep-ph/ H.Drescher, A.Dumitru,A.Hayashigaki,Y.Nara, nucl-th/

Elliptic flow PHOBOS 200 GeV Statistical errors only Plots from G. Roland, CERN HIF, May ‘06 Elliptic flow in CuCu seen to be stronger than may be expected on the basis of ellipticity computed in “standard” Glauber model

Baryon transport Baryon junctions: the carriers of baryon number? Rossi, Veneziano

Baryon transport BRAHMS: nucl-ex/ “Nuclear stopping in Au+Au collisions at  S NN = 200 GeV”

Baryon transport Plot from R.Debbe; BRAHMS data The net charge is fitted to : A cosh(y/b) DK, PLB378(96)238  2 =7.4/6 A = 8.5  0.3 b = 2.4  0.1 Total number of protons in y range: - 3, 3

Baryon transport What is the mechanism of baryon production?

Baryon transport Enhancement seen also in pA collisions - not entirely final-state effect P.B. Straub et al., PRL 68 (1992) FNAL experiments measuring R (W / Be) for identified particles at sqrt(s) of 27.4 and 51.3 GeV. J.Velkovska

QCD phase diagram and the tricritical point Figures from F. Karsch; n f =2, or 2+1 “massive” s quark

Where is the tri-critical point located? Plot from M. Stephanov Fit by Becattini et al. central A+A AGS SPS RHIC Plot from F.Becattini, G.Roland

Where is the tri-critical point located? Fit by Becattini et al. central A+A AGS SPS RHIC F. Karsch:

Energy dependence of particle ratios SPSRHIC

Energy dependence of particle ratios BRAHMS, PRL90, 10231

What are the dynamical degrees of freedom in the plasma? Let us look at the charge fluctuations in sQGP: Hadron resonance gas Dynamical quarks QQ bound states S.Ejiri, F.Karsch and K.Redlich

Fluctuations of baryon number are enhanced near the critical point From F. Karsch K.Rajagopal, E.Shuryak, M.Stephanov

Summary The study of energy dependence of multi-particle production in heavy ion collisions will allow a detailed study of the QCD properties at high density and temperature, the mechanisms of baryon transport, and may allow to locate the position of the tri-critical point on the phase diagram