Soft Physics in Au Au Collisions at RHIC

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Soft Physicsin AuAu Collisions at RHIC
Peter F. Kolb

• AGS/RHIC users meeting
• Brookhaven National Laboratory
• May 16, 2003

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Modeling the Expansion Dynamics
formalism
scattering of partons and hadrons kinetic
transport equations collision terms
continuity equations energy, momentum
conservation equation of state
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Testing the Nuclear Equation of State
In particular - verification of the predicted
QCD phase change - study a new state of matter
free quarks and gluons - investigate its
thermodynamic properties
4 x 10
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Nuclear wallchart _at_ www.lbl.gov
F. Karsch, Nucl. Phys. A 698 (2002) 1999 U.
Heinz, Nucl. Phys. A 685 (2001) 414
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Hydrodynamic Evolution (b0)
Equations of Motion
Equation of State
here a resonance gas EoS for Tcrit lt 165 MeV with
mixed phase and ideal gas EoS above
Initial Configuration
from an optical Glauber calculation
t0 0.6 fm
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Evolution of Non-Central Collisions
(here b7 fm)
evolution of the energy density
spatial eccentricity
momentum anisotropy
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Particle Spectra of Central Collisions AuAu _at_
200 A GeV
Data PHENIX NPA715(03)151 STAR NPA715(03)458
PHOBOS NPA715(03)510 BRAHMS NPA715(03)478 Hydro
-calculations including chemical potentials PFK
and R. Rapp, Phys. Rev. C 67 (03) 044903
Particle spectra hydro vs. data
Parameters ?0 0.6 fm/c s0 110 fm-3 s0/n0
250 TcritTchem165 MeV Tdec100 MeV
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Single Particle Spectra W
STAR collab., Nucl. Phys. A 715 (2003) 470c Hydro
calculation as in PFK and R.Rapp, Phys. Rev. C 67
(2003) 044903
The Omega resonance shows as strong transverse
flow as the lighter hadrons. It appears to fully
participate in the collective expansion in the
partonic as well as in the hadronic stage
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Transverse Momentum and Trans. Energy
PHENIX collab., Nucl. Phys. A 715 (2003) 151c
PHENIX collab., Nucl. Phys. A 715 (2003) 151c
Transverse momenta as function of centrality are
well under control as long as the collisions are
not too peripheral. Transverse energy agrees for
all centralities.
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Elliptic Flow at RHIC (130)
Heinz, PFK, NPA 702(02)269 Huovinen et al. PLB
503(01)58 Teaney et al. PRL 68(01)4783 Hirano,
PRC 65(01)011901
Mass, momentum and centrality dependence are well
described up to pT 2 GeV and b 7 fm
Over 99 of the emitted particles follow hydro
systematics
STAR collab., PRL 87 (2001) 182301
STAR, J. Phys. G 28 (2002) 20
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Elliptic flow requires strong rescattering
PFK et al., PLB 500 (2001) 232 D. Molnar and M.
Gyulassy, NPA 698 (2002) 379
Cross-sections and/or gluon densities of at some
10 to 80 times the perturbative estimates are
required to deliver sufficient anisotropies. At
larger pT the experimental results (as well as
the parton cascade) saturate, indicating
insufficient thermalization of the rapidly
escaping particles to allow for a hydrodynamic
description.
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Elliptic flow requires rapid thermalization
PFK, J. Sollfrank and U. Heinz, PRC 62 (2000)
054909

• Free flow for an interval ?t changes the initial
  distribution function .
• For massless particles in the transverse plane (
  )
• Reduced spatial anisotropy
• ? as , the elliptic flow is reduced
  accordingly. With typical dimensions
  of non-central collisions, one obtains a
  reduction of 30 for ?t 2 fm/c.

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Sensitivity on the Equation of State
Teaney, Lauret, Shuryak, nucl-th/0110037
PFK and U. Heinz, nucl-ex/0204061
The data favor an equation of state with a soft
phase and a latent heat De between 0.8 and 1.6
GeV/fm3
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Elliptic flow at finite rapidity
T. Hirano and K. Tsuda, nucl-th/020868
Boost invariance and thermodynamic concepts seem
to be justified over a pseudo-rapidity interval
from -1.5 lt h lt 1.5 Observables at larger
rapidities operate at higher baryon chemical
potential (? close to the critical point!).
Larger rapidities also hold pre-equilibrium
information (? directed flow!)
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Summary
Hydrodynamics is also the tool to describe the
underlying dynamics of density fields over which
hard probes propagate
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Disclaimer
There are some well know diseases in this picture

• complete arrogance w.r.t. viscosity effects,
  which gets more and more severe around decoupling

- this is probably related to the disagreement of
the HBT radii and geometrical aspects of the
source
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Summary
Hydrodynamics is also the tool to describe the
underlying dynamics of density fields over which
hard probes propagate