Collective Dynamics at RHIC Aihong Tang

Aihong Tang QuarkMatter 06, Shanghai

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Collective Collective Dynamics Dynamics at at RHICRHIC

Aihong Tang


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Outline:Outline:

- How perfect? How perfect?

- Is the “Is the “perfect liquidperfect liquid” a unique explanation?” a unique explanation?

- How do we probe the How do we probe the initial conditioninitial condition??

- When, and how is the When, and how is the collectivitycollectivity achieved? achieved?

- Can we test the Can we test the thermalization?thermalization?

- How do we divide How do we divide soft physicssoft physics and hard physics? and hard physics?

- Scaling of soft physicsScaling of soft physics

- How does the How does the hadronic interactionhadronic interaction contribute to the collective contribute to the collective motion?motion?

- Phase transitionPhase transition and and Critical End PointCritical End Point


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How Perfect ?

v2/ approaches the limit of ideal hydrodynamicsViscosity reduces v2 Viscosity needs to be small in order to explain data

STAR, PRC 66 034904 (2002)

D. Teaney, PRC 68 034913 (2003)

Almost nothing can be more liquid-like than it !

€

Γs =4

3η (e + p)


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Is “perfect liquid” a unique explanation ?

- Is it Glauber + perfect liquid or, CGC + viscous matter?

- It is important to understand the initial condition !

CGC Glauber

A. Adil, et al. nucl-th/0605012 (2006)

T. Hirano, RHIC & AGS Users Mtg 06

CGC > Glauber


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How do we probe the initial condition ?

At higher pt CGC predicts greater rapidity twist away from the beam axis than the bulk.

v2 fluctuation is directly related to the fluctuation of initial conditions.Considerable amount of v2 fluctuation (36%-40%) in data is observed.A. Adil, M. Gyulassy and

T.Hirano. Phys. Rev. D 73 074006 (2006)

Flow direction of spectators

Flow direction of spectators

Probe the initial condition by following its footprints in flow observables !

P. Sorensen’s talk, 18Nov. Sat. Parallel 2.4

D. Hofman, Phobos highlight talk, this QM


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When, and how is the collectivity achieved?

Y. Lu et al. Journal of Phys. G 32 1121 (2006)F. Liu’s talk, 19 Nov. Sun Parallel3.4

and are less affected by hadronic interactions and they show sizable flow !Hadronic interactions at a later stage do not produce enough v2

PHENIX, nucl-ex/0608033 (2006)

D.Teaney, J.Lauret and E. Shuryak, nucl-th/0110037

Collectivity is achieved fast and early (from pre-hadronic phase).

STAR preliminary

Y. Bai’s talk, this QuarkMatter


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Can we test the thermalization ?

Taken the systematical error into account, the ratio of v4/v22 does not

contradict to theoretical calculations.

Y. Bai’s talk, 18Nov. Sat. Parallel 2.4


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Au+Au 200 GeV

P. Kolb and R. Rapp, Phys. Rev. C 67 044903 (2003)

What is soft, what is hard ?

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.


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What is soft, what is hard ?

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

S. Blyth’s talk, 19Nov. Sun. Parallel 3.1

STAR preliminary


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Scaling of soft physics

D. Das & Z. Chajeck

€

V = (NPart

2)αV0

=1

=2/3

=1/3

Evidence from HBT and Strangeness production shows that length plays an important role in soft physics.

M. Lamont, SQM06. Curve : K. Redlich


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Scaling of soft physics

PHOBOS, nucl-ex/0610037

D.Teaney, J.Lauret and E. Shuryak, nucl-th/0110037

Volume

Length

If plotted as a function of length, good linearity is observed for a few keyobservables from soft sector.

Length is directly related to the averagenumber of interactions for a particle on its way out !

S. V

olo

sh

in’s

talk

, 18

Nov. S

at. P

ara

llel

2.4

STAR preliminary

For fixed b = 6 fm


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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.


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v1 from different collision systems

v1 is found being independent of collision systems.

G. W

an

g’s

talk

, 19

Nov. S

un

. Para

llel 3

.4


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Longitudinal scaling

PHOBOS Phys. Rev. Lett. 97 012301 (2006)

PHOBOS nucl-ex/0610037 (2006)

Limiting fragmentation holds for different energies, collision systems and harmonics.

Y. B

ai’s

talk

, 18

Nov. S

at.

Para

llel 2

.4

G. W

an

g’s

talk

, 19

Nov. S

un

. P

ara

llel 3

.4

STAR preliminary

STAR preliminary


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NA 49, Phys. Rev. C 68 034903 (2003)

Does the proton flow collapse?

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)

“Anti-Flow” observed 1st Order Phase Transition ?


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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)


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AuAu 62 GeV

STAR Phys. Rev. C 73 034903 (2006)


“Anti-Flow” --- an inconclusive topic but has good potential


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Are we close to the Critical End Point ?

C. Nonaka and M. Asakawa, Phys. Rev. C. 71 044904 (2005)

M. Stephanov, hep-ph/0402115 (2006)

R. Gavai and S. Gupta hep-lat/0509151 (2006)

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

Hydrodynamical calculation with CEP shows that CEP acts as an attractor of isentropic trajectories

Look forward to low energy scan program at RHIC


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Summary:Summary:

- Rich results from RHIC support a Hydrodynamic expansion of a thermalized 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. 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 Understanding the initial condition plays a key role in understanding what happens thereafter. Anisotropic flow may help us constraint initial conditions.happens thereafter. Anisotropic flow may help us constraint initial conditions.

- The PID dependence of division between soft physics and hard physics will 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 help us understanding not only the physics in the soft sector, but also the physics at intermediate pphysics at intermediate ptt..

- A few key observables from soft physics are found scaling with length, which 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 is directly related to the average number of interaction for a particle before the freeze-out.freeze-out.

- Limiting fragmentation holds for different collisions energies, systems and Limiting fragmentation holds for different collisions energies, systems and flow harmonics.flow harmonics.

- Theoretical work suggests that we might be close to the Critical End Point -- Theoretical work suggests that we might be close to the Critical End Point -- look forward to the future energy scan program at RHIC.look forward to the future energy scan program at RHIC.

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Collective Dynamics at RHIC Aihong Tang