Collective Flow in Heavy-Ion Collisions

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Collective Flow in Heavy-Ion Collisions

• Kirill Filimonov (LBNL)

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What is Flow in Heavy-Ion Collisions?

• Collective motion characterized by space-momentum
  correlation of dynamic origin

• Concept from Hydrodynamics
• - hot and compressed matter
  behaves like a compressible fluid

Types of Flow

• axially symmetric radial flow
• azimuthally anisotropic transverse flow

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Collective Behavior in non-central Heavy Ion
Collisions
Low energy heavy-ion collisions E/A25 MeV
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Collective Behavior in non-central Heavy Ion
Collisions
Relativistic heavy-ion collisions E/A0.4-10 GeV
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Collective Behavior in non-central Heavy Ion
Collisions
Passage time 2R/(ßcm?cm)

• 15 fm/c at 1 GeV/nucleon
• 5.4 fm/c at 10 GeV/nucleon
• 1.4 fm/c at 160 GeV/nucleon

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View in transverse plane
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Directed (sideward) Flow
Example E877 (AGS, 11 AGeV)
py
protons deuterons
px
ltpxgt ?0
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Out-of-plane squeeze-out (spectator blocking)
Azimuthal anisotropy in momentum space
(elliptic flow)
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In-plane elliptic flow (due to pressure gradient)
Azimuthal anisotropy in momentum space
(elliptic flow)
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Interplay of passage/expansion times
Passage time 2R/(ßcm?cm) Expansion time R/cs
cscvdp/de - speed of sound
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Sensitivity to nuclear EOS
Science, Vol 298, Issue 5598, 1592-1596, 22
November 2002Determination of the Equation of
State of Dense Matter Pawel Danielewicz, Roy
Lacey, William G. Lynch
Directed Flow
Elliptic flow
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Elliptic flow at RHIC
Longitudinal and transverse expansion gt no
influence of spectator matter at midrapidity
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Elliptic flow at RHIC
Flow
Y
Out-of-plane
In-plane
Reaction plane
Flow
X
Re-interactions ? FLOW Re-interactions among
what? Hadrons, partons or both? In other words,
what equation of state?
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Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b 6.5 fm
b 4 fm
central collisions
midcentral collisions
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Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b 10 fm
b 6.5 fm
b 4 fm
peripheral collisions
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v2 Excitation Function
Rich structure Transition from in-plane to
out-of-plane and back to in-plane
emission Geometry effect in addition to
(smooth?) change in pressure
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v2 vs Energy Density
Steady increase with energy density Close to
hydrodynamic limit for most central collisions at
RHIC
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Elliptic flow gt sensitivity to early system

• Elliptic flow
• evidence ofcollective motion
• sensitive to early pressure
• evidence for
• early thermalization
• QGP in early stage

Hydrodynamic calculation of system evolution
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Quark-number scaling
At intermediate pT v2 appears to depend on
quark-number For pT/n gt 0.6 GeV/c, v2 scales with
the number of quarks n, as predicted for hadron
formation by quark coalescence
Pions deviate perhaps because they are goldstone
bosons but also because of resonance decay
contributions.
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Conclusions and Outlook

• Elliptic flow at RHIC gt Evidence for early
  pressure
• First time hydro works in heavy ion collisions!
• Indications of re-interaction between constituent
  quarks
• Will charm flow at RHIC?