Transcript Collective dynamics in heavy-ion collisions (25) Aihong Tang

Collective
Dynamics
at
RHIC
 Aihong Tang
Aihong Tang
QuarkMatter 06, Shanghai
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Outline:
- How perfect?
- Is the “perfect liquid” a unique explanation?
- How do we probe the initial condition?
- When, and how is the collectivity achieved?
- Can we test the thermalization?
- How do we divide soft physics and hard physics?
- Scaling of soft physics
- How does the hadronic interaction contribute to the collective
motion?
- Phase transition and Critical End Point
Aihong Tang
QuarkMatter 06, Shanghai
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How Perfect ?
4
s  (e  p)
3

D. Teaney, PRC 68 034913 (2003)
v2/ approaches the limit of ideal
hydrodynamics
Viscosity reduces v2
Viscosity needs to be small in order to
explain data
Almost nothing can be more liquid-like
than it !
STAR, PRC 66 034904 (2002)
Aihong Tang
QuarkMatter 06, Shanghai
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Is “perfect liquid” a unique explanation ?
CGC
Glauber
CGC > Glauber
A. Adil, et al. nucl-th/0605012 (2006)
-
Is it Glauber + perfect liquid or,
CGC + viscous matter?
-
It is important to understand the initial
condition !
T. Hirano, RHIC & AGS Users Mtg 06 Aihong Tang
QuarkMatter 06, Shanghai
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How do we probe the initial condition ?
Flow direction of spectators
At higher pt CGC predicts greater
rapidity twist away from the beam
axis than the bulk.
Flow direction of spectators
A. Adil, M. Gyulassy and T.Hirano.
Phys. Rev. D 73 074006 (2006)
v2 fluctuation is directly related to
the fluctuation of initial conditions.
Considerable amount of v2
fluctuation (36%-40%) in data is
observed.
D. Hofman, Phobos highlight talk, this QM
P. Sorensen’s talk, 18Nov. Sat. Parallel 2.4
Aihong Tang
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Probe the initial condition by
following
its
footprints
in
flow
observables
!
QuarkMatter 06, Shanghai
When, and how is the collectivity achieved?
STAR preliminary
Y. Bai’s talk,
this QuarkMatter
PHENIX, nucl-ex/0608033 (2006)
D.Teaney, J.Lauret and E. Shuryak, nucl-th/0110037
 and  are less affected by
hadronic interactions and they
show sizable flow !
Hadronic interactions at a later
stage do not produce enough v2
Y. Lu et al. Journal of Phys. G 32 1121 (2006)
Aihong Tang
F. Liu’s talk, 19 Nov. Sun Parallel3.4
Collectivity is achieved fast and
early (from pre-hadronic phase).
QuarkMatter 06, Shanghai
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Can we test the thermalization ?
Y. Bai’s talk, 18Nov. Sat. Parallel 2.4
Taken the systematical error into account, the ratio of v4/v22 does not
contradict to theoretical calculations.
Aihong Tang
QuarkMatter 06, Shanghai
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What is soft, what is hard ?
Au+Au 200 GeV
P. Kolb and R. Rapp,
Phys. Rev. C 67 044903 (2003)
P.F. Kolb and U. Heinz, nucl-th/0305084
Hydro breaks down around 1.5~2 GeV/c for ,k and p, but
works well up to pt ~ 4 GeV/c for .
Whether a pt range is for “Soft physics” or “Hard physics”
depends on particle species.
Aihong Tang
QuarkMatter 06, Shanghai
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What is soft, what is hard ?
STAR preliminary
S. Blyth’s talk,
19Nov. Sun. Parallel 3.1
Coalescense/recombination model works at different pt range
for different particle species.
Understanding the division between soft and hard physics is a
key to understand particle ratios (and other physics) at
intermediate pt
Aihong Tang
QuarkMatter 06, Shanghai
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Scaling of soft physics
M. Lamont, SQM06. Curve : K. Redlich
V (
N Part 
) V0
2

Evidence from HBT and Strangeness
production shows that length plays an
important role in soft physics.
D. Das & Z. Chajeck
Aihong Tang
QuarkMatter 06, Shanghai
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Scaling of soft physics
S. Voloshin’s talk, 18Nov. Sat. Parallel 2.4
PHOBOS, nucl-ex/0610037
Volume
STAR preliminary
Length
If plotted as a function of length, good
linearity is observed for a few key
observables from soft sector.
For fixed b = 6 fm
D.Teaney, J.Lauret and E. Shuryak,
nucl-th/0110037
Length is directly related to the average
number of interactions for a particle on
its way out !
Aihong Tang
QuarkMatter 06, Shanghai
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How does the hadronic interaction contribute to the collective motion?
Y. Lu et al. Journal of Phys. G 32 1121 (2006)
F. Liu’s talk, 19 Nov. Sun Parallel3.4
Hadron-string transport models can qualitatively
reproduce the mass splitting at low pt and the NCQ
scaling at intermediate pt while it fails by 40% to exhaust
the absolute value.
Aihong Tang
QuarkMatter 06, Shanghai
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v1 from different collision systems
G. Wang’s talk, 19Nov. Sun. Parallel 3.4
v1 is found being independent of collision systems.
Aihong Tang
QuarkMatter 06, Shanghai
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Longitudinal scaling
G. Wang’s talk, 19Nov. Sun.
Parallel 3.4
STAR preliminary
PHOBOS Phys. Rev. Lett. 97 012301 (2006)
Limiting fragmentation holds for different energies, collision systems and harmonics.
PHOBOS nucl-ex/0610037 (2006)
Aihong Tang
QuarkMatter 06, Shanghai
Y. Bai’s talk, 18Nov. Sat.
Parallel 2.4
STAR preliminary
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Does the proton flow collapse?
NA 49, Phys. Rev. C 68 034903 (2003)
“Anti-Flow” observed 
1st Order Phase Transition ?
Brachmann, Soff, Dumitru, Stocker, Maruhn, Greiner Bravina, Rischke , PRC 61 (2000) 024909.
L.P. Csernai, D. Roehrich PLB 458, 454 (1999)
M.Bleicher and H.Stocker, PLB 526,309(2002)
H. Stoecker, Nucl. Phys. A750 121 (2005)
Aihong Tang
QuarkMatter 06, Shanghai
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Does the proton flow collapse?
flow
antiflow
Brachmann, Soff, Dumitru, Stocker, Maruhn, Greiner Bravina, Rischke , PRC 61 (2000) 024909. L.P.
Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002)
Aihong Tang
QuarkMatter 06, Shanghai
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Does the proton flow collapse?
AuAu 62 GeV
STAR Phys. Rev. C 73 034903 (2006)
“Anti-Flow” --- an inconclusive topic but has good potential
Aihong Tang
QuarkMatter 06, Shanghai
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Are we close to the Critical End Point ?
Recent lattice calculation
suggests that the CEP has a
small chemical potential, which
places it in the range of
observability in the energy
scans at RHIC
R. Gavai and S. Gupta
hep-lat/0509151 (2006)
M. Stephanov,
hep-ph/0402115 (2006)
Hydrodynamical calculation
with CEP shows that CEP acts
as an attractor of isentropic
trajectories
Look forward to low energy
scan program at RHIC
C. Nonaka and M. Asakawa,
Phys. Rev. C. 71 044904 (2005)
Aihong Tang
QuarkMatter 06, Shanghai
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Summary:
- Rich results from RHIC support a Hydrodynamic expansion of a thermalized
fluid in which the collectivity is achieved fast and at the very early time.
- Understanding the initial condition plays a key role in understanding what
happens thereafter. Anisotropic flow may help us constraint initial conditions.
- The PID dependence of division between soft physics and hard physics will
help us understanding not only the physics in the soft sector, but also the
physics at intermediate pt.
- A few key observables from soft physics are found scaling with length, which
is directly related to the average number of interaction for a particle before the
freeze-out.
- Limiting fragmentation holds for different collisions energies, systems and
flow harmonics.
- Theoretical work suggests that we might be close to the Critical End Point -look forward to the future energy scan program at RHIC.
Aihong Tang
QuarkMatter 06, Shanghai
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