Elliptic and Radial Flow in High Energetic Nuclear Collisions

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Elliptic and Radial Flow in High Energetic
Nuclear Collisions

• Marcus Bleicher ( Xianglei Zhu)
• Institut für Theoretische Physik
• Goethe Universität Frankfurt
• Germany

2
Thanks to

• Elena Bratkovskaya
• Sascha Vogel
• Stephane Haussler
• Hannah Petersen
• Diana Schumacher
• Nu Xu

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The tool UrQMDv2.2

• Non-equilibrium transport model
• Hadrons and resonances
• String excitation and fragmentation
• Cross sections are parameterized
• via AQM or calculated by detailed balance
• pQCD hard scattering at high energies
• Generates full space-time dynamics of hadrons
  and strings

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Transverse Momentum Distributions Proton-Proton

• PP works well
• pQCD needed at RHIC
• PYTHIA included in
• UrQMD 2.x and HSD

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Proton-Nucleus

• pA is well under control
• CC and SiSi are also under control
• What about AA?

Inv. slope
System size
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Transverse mass spectra

• Standard UrQMD and HSD underestimate the data
• Additional resonances of 2-3 GeV mass may
  improve the description

mt-m0
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Inverse slope systematics

• Step claimed to be signature of QGP onset
  (Gazdzicki)
• High mass resonances improve
• the description at low and high energies
• How can we test those scenarios??use v2 to
  disentangle early and late stage

E_CM (AGeV)
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Anisotropic flow
Fourier expansion of the transverse angular
distribution of the emitted particles
Reaction Plane
v1 directed flow V2 -- elliptic flow
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Elliptic flow
coordinate-space-anisotropy ?
momentum-space-anisotropy
y
py
x
px

• V2 of low pt particles is the good measure the
  EOS of the fireball in the early stage.
• V2 of high pt particles is the good measure of
  jet energy loss through the medium.

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Hints from elliptic flow

• High mass resonances can not explain
  scaled v2 above 40 AGeV
• Data shows saturation of scaled v2
• Strong hint for large pressure
• and short mean free paths in the
• early stage of the reaction
• already from 30 AGeV on !

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Partonic dof already atlow SPS energy

• Breakdown of v2/ltptgt scaling in model coincides
  with onset of partonic matter? signals
  onset of change of EoS in the early stage

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V2 at RHIC

• Magnitude of v2 is large
• Meson-baryon ordering
• Constituent quark scaling
• Decrease of v2 at high ptAre these unique QGP
  signatures?

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Elliptic flow Centrality dependence

• Integral flow

STAR data is from nucl-ex/0409033
V2 from UrQMD is about 50 smaller than the
data, Left space for parton rescattering?
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Cumulant method results

• Integral flow

In the most central bin The fluctuations give
larger v26 but smaller v24 In the very
peripheral bins The fluctuations give larger
v26 and v24 Agree with the prediction of MCG
model BUT In the semi-central bins the v2
fluctuations can be neglected.
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Cumulant method results

• Comparison to STAR data

Good agreement of the ratios with STAR
data. Decrease of g2 at peripheral bins are also
reproduced. (the g2 decrease is possibly from the
v2 fluctuations)
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Cumulant method results

• Differential flow

At large eta, the non-flow effects are less
obvious. If the v2 fluctuations are also
negligible to the cumulant method, the v22,
v24 and v26 should all agree with the exact
v2.
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Cumulant method results

• Differential flow

v22 is heavily affected by the non-flow effects
especially at large pt. The non-flow effects
have been eliminated in v24 and v26. But
v24 is still a little larger than the exact v2.
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V2(pt) from UrQMD
Red--Mesons
Blue-Baryons
1) Clear separation of meson and baryon v2 2) Low
pt, v2(meson)gtv2(baryon) 3) High pt,
v2(m)ltv2(b) 4) The v2s of multi-strange baryons
are comparable to light baryons
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NCQ-scaling
Notemulti-strange baryons follow the normal
matter
NCQ-scaling of v2 is roughly reproduced in UrQMD!
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Summary

• At RHIC (transport models w/ strings and
  hadrons)
• Part of v2 might also come from hadronic stage
• Mass ordering is correct
• Constituent quark scaling (w/o ReCo!)
• non-flow correlations are correct
• However, transport models w/o QGP produce to few
  pressure in the early stage above 30 GeV