Title: Collective Flow in Heavy-Ion Collisions
1Collective Flow in Heavy-Ion Collisions
2What 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
3Collective Behavior in non-central Heavy Ion
Collisions
Low energy heavy-ion collisions E/A25 MeV
4Collective Behavior in non-central Heavy Ion
Collisions
Relativistic heavy-ion collisions E/A0.4-10 GeV
5Collective 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
6View in transverse plane
7Directed (sideward) Flow
Example E877 (AGS, 11 AGeV)
py
protons deuterons
px
ltpxgt ?0
8Out-of-plane squeeze-out (spectator blocking)
Azimuthal anisotropy in momentum space
(elliptic flow)
9In-plane elliptic flow (due to pressure gradient)
Azimuthal anisotropy in momentum space
(elliptic flow)
10Interplay of passage/expansion times
Passage time 2R/(ßcm?cm) Expansion time R/cs
cscvdp/de - speed of sound
11Sensitivity 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
12Elliptic flow at RHIC
Longitudinal and transverse expansion gt no
influence of spectator matter at midrapidity
13Elliptic 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?
14Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b 6.5 fm
b 4 fm
central collisions
midcentral collisions
15Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b 10 fm
b 6.5 fm
b 4 fm
peripheral collisions
16v2 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
17v2 vs Energy Density
Steady increase with energy density Close to
hydrodynamic limit for most central collisions at
RHIC
18Elliptic 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
19Quark-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.
20Conclusions 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?