Energy and mB dependence in heavy ion collisions

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Energy and mB dependencein heavy ion collisions
From high mB to high energy, BNL, June 5, 2006

• D. Kharzeev
• BNL

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Outline

• Global observables
• Baryon transport
• QCD phase diagram and the tricritical point

• o hadron multiplicities
• elliptic flow
• identified hadrons

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From CGC to Quark Gluon Plasma
T. Ludlam, L. McLerran, Physics Today, October
2003
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The phase diagram of high energy QCD
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Phase diagram of high energy QCD
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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-partic
le distances 1/T)
number of flavors
number of colors
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Asymptotic freedom and Landau levels of 2D
parton gas
The effective potential sum over 2D Landau levels
V
Paramagnetic response of the vacuum
H
1. The lowest level n0 of radius
is unstable!
2. Strong fields
Short distances


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QCD and the classical limit
Classical dynamics applies when the action
is large in units of the Planck
constant (Bohr-Sommerfeld quantization)
(equivalent to setting )
weak field
gt Need weak coupling and strong fields
.i
strong field
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Building up strong color fieldssmall x (high
energy) and large A (heavy nuclei)
Bjorken x the fraction of hadrons momentum
carried by a parton high energies s open access
to small x Q2/s
the boundary of non-linear regime partons
of size 1/Q gt 1/Qs overlap
Large x
small x
Because the probability to emit an extra gluon is
as ln(1/x) 1, the number of gluons at small
x grows the transverse area is limited
transverse density becomes large GLR
McLerran, Venugopalan
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Hadron multiplicitiesthe effect of parton
coherence
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Semi-classical QCD and total multiplicities in
heavy ion collisions
Expect very simple dependence of multiplicity .on
atomic number A / Npart
Npart
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Classical QCD in action
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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
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Classical QCD in action
The data on hadron multiplicities in Au-Au and
d-Au collisions support the semi-classical
picture
KLN
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Initial state parton saturation?
QM2002 nucl-ex/0212009
200 GeV
130 GeV
Preliminary 19.6 GeV
Kharzeev, Levin, Nardi, hep-ph/0111315
l0.25 from fits to HERA data
xG(x)x-l Describes energy dependence
correctly!
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Predictions for the LHC
KLN, hep-ph/0408050
talk by A.Stasto
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How dense is the produced matter?
The initial energy density achieved
mean transverse momentum of produced gluons
about 100 times nuclear density !
the density of the gluons in the transverse plane
and in rapidity
gluon formation time
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What happens at such energy densities?
Phase transitions deconfinement Chiral
symmetry restoration UA(1) restoration
Data from lattice QCD simulations F. Karsch et al
critical temperature 1012 K cf temperature
inside the Sun 107 K
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Viscosity of sQGP
A.Nakamura and S.Sakai, hep-lat/0406009
Perfect fluid
KSS bound strongly coupled SUSY QCD classical
supergravity
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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 gt Small entropy
production
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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/0511046
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How small is really the viscosity?
KLN initial conditions lead to larger ellipticity,
T.Hirano, U.Heinz, DK, R.Lacey, Y. Nara,
hep-ph/0511046
this is not an artifact of a particular model for
the gluon distribution, but a generic feature of
saturation
H.Drescher, A.Dumitru,A.Hayashigaki,Y.Nara,
nucl-th/0605012
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Elliptic flow
PHOBOS 200 GeV Statistical errors only
Elliptic flow in CuCu seen to be stronger than
may be expected on the basis of ellipticity
computed in standard Glauber model
Plots from G. Roland, CERN HIF, May 06
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Baryon transport
Baryon junctions the carriers of baryon number?
Rossi, Veneziano
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Baryon transport
BRAHMS nucl-ex/0312023 Nuclear stopping in
AuAu collisions at ?SNN 200 GeV
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Baryon transport
The net charge is fitted to A cosh(y/b) DK,
PLB378(96)238 ?27.4/6 A 8.5? 0.3 b 2.4? 0.1
Total number of protons in y range -3, 3
Plot from R.Debbe BRAHMS data
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Baryon transport
What is the mechanism of baryon production?
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Baryon transport
Enhancement seen also in pA collisions - not
entirely final-state effect
J.Velkovska
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.
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QCD phase diagram and the tricritical point
Figures from F. Karsch nf 2, or 21 massive
s quark
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Where is the tri-critical point located?
Plot from M. Stephanov
Fit by Becattini et al.
AGS
central AA
SPS
Plot from F.Becattini, G.Roland
RHIC
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Where is the tri-critical point located?
F. Karsch
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Energy dependence of particle ratios
SPS
RHIC
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Energy dependence of particle ratios
BRAHMS, PRL90, 10231
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What are the dynamical degrees of freedom in the
plasma?Let us look at the charge fluctuations in
sQGP
Hadron resonance gas
QQ bound states
Dynamical quarks
S.Ejiri, F.Karsch and K.Redlich
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Fluctuations of baryon numberare enhanced near
the critical point
K.Rajagopal, E.Shuryak, M.Stephanov
From F. Karsch
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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