event anisotropy at star

2009 RHIC & AGS Annual Users' Meeting

Event Anisotropy at STAR

Na Lifor the STAR collaboration

Brookhaven National LaboratoryInstitute of Particle Physics, Central China Normal University

Na Li for STAR collaboration (BNL/IOPP) 2

Introduction

Results and discussions Partonic collectivity Number of Quarks Scaling Ideal Hydrodynamic

Summary

Outline

Na Li for STAR collaboration (BNL/IOPP)

- Identify and study the properties of the matter (EOS) with partonic degrees of freedom.

- Explore the QCD phase diagram.

Physics Goals at RHIC

HydrodynamicFlow Collectivity Local

Thermalization=

3


Coordinate-SpaceAnisotropy

Momentum-SpaceAnisotropy

2 2

2 2

y x

y x

12 cos 2 , tan ( )y

x

pv

p

Elliptic Flow (v2)

Elliptic flow: information about the early stage collision dynamics Strange hadron: less sensitive to hadronic rescattering Good probe of the early stage of the collision

partonic hadronic

interactions

pressure gradient pressure gradient collective flow collective flow

D, , Ω, Ξ, Λ, , K, p


STAR Detector

TOF

TPC

FTPC

Time Projection Chamber: Main TPC: |η| < 1;

Time Of Flight: Particle identification

Forward TPC: 2.5 < |η| < 4.0; Rapidity gap could reduce “non-flow” effects;

Zero Degree Calorimeter: |η| > 6.0;

Full Azimuthal

ZDC

(SMD)


Partonic Collectivity

Final word on partonic collectivity at RHIC!

Open points: PHENIX π and p: nucl-ex/0604011v1NQ inspired fit: X. Dong et al. Phy. Let. B 597 (2004) 328-332


NQ Scaling at Large pT

Ideal hydro: P. Huovinen and P. V. Ruuskanen, Annu. Rev. Nucl. Part. Sci. 56, 163 (2006) and private communication

Centrality: 0 - 80% Systematic

uncertainties FTPC event plane

NQ Scaling Protons , probably Λ

too, start deviating from the scaling at large pT

STAR preliminary

D. Molnar and S. Voloshin, PRL91, 092301 (2003)R. J. Fries et. al., PRC68, 044902 (2003)V. Greco et. al, PRC68, 034904 (2003)J. Jia and C. Zhang, PRC75, 031901(R) (2007)...Narrow band: 5% v2 non-flow for reconstructed particles

Wide band: 15% v2 non-flow for π and p


v2 in Cu + Cu (Au +Au) at 200 and 62.4 GeV are comparable within statistical errors

v2 at Cu + Cu 62.4 GeV ~ 12.5 M events- Same procedure used for 200 GeV. - Event plane resolution is 0.088 0.004 in 0 - 60 %, about factor 2 smaller than that in 200 GeV due to lower multiplicity.

STAR Au + Au 200 GeV : PRC77, 054901 (2008) Au + Au 62.4 GeV : PRC75, 054906 (2007)

Energy Dependence

STAR preliminary


STAR preliminary

Au + Au at 200 GeV

Au + Au : PRC77, 054901 (2008)

System Size Dependence

v2 scaled by eccentricity Remove the initial

geometry effect

v2 seems solely depending on initial geometry and number of participant in 200 GeV collisions

v2 ∝ v2(ε, Npart)


Ideal Hydro Test (I)Ideal hydro: P. Huovinen, private communication

Ideal hydro fails to reproduce the data.

Fluctuation of v2? Viscosity ? Incomplete thermalization ?

STAR preliminary

Phys. Rev. C 77 (2008) 54901

Au+Au at 200 GeV


Ideal Hydro Test (II)

v4/v22 results suggest that ideal hydro limit is not reached

Need to study η/s to see how far away we are from ideal hydro limit

Borghini & Ollitrault, PLB 642 227 (2006)

Au+Au at 200 GeV0-80%


Ideal Hydro Limit Even in central Au + Au collisions, fitting results indicate

that the system is still away from hydro limit

12

v2/ε scaling: S. Voloshin (for STAR Collaboration), J.Phys.G34(2007)S883PHENIX π, K and p: nucl-ex/0604011v1CGC eccentricity: H.J. Drescher and Y. Nara, PRC 76 041903 (2007), H.J. Drescher and Y.Nara, PRC 75 034905 (2007)

Ideal Hydro Limit

STAR preliminary

Hydro limit

ΞΛ K h

STAR preliminary


Caveats :Transport model motivated – best for dilute systemNo phase transitionAveraged over all phases – effective quantity

s

0.316T

1

K

R

Effective η/s from transport model motivated approach

Hunting the Perfection

η/s(CGC) < η/s(Glauber)

Includes hadronic effect – Large η/s

STAR preliminary hh


Partonic collectivity at RHIC demostrated! Test of local thermalization is the next step.

NQ scaling: In Au + Au collisions, p and Λ start deviating from the scaling at

large pT. The scaling seems also work in Cu+Cu collisions.

Ideal hydrodynamic predictions test:

(a) Hydro fails to reproduce the centrality dependence of v2.

(b) v4/v22 data larger than ideal hydro prediction.

Ideal hydro limit (a) A model dependent fit shows that the system has not reached the hydro limit. (b) Heavier particles are closed to hydro limit. (c) η/s is a few times of the conjectured quantum limit.

Summary


Backup


Knudsen number K

Knudsen number degrees of equilibration Reach hydro limit when

K 0 Transport model results

(symbols) can be reproduced by the formula below

K0 = 0.7, cs2 = 1/3

v 2

hydro limit

σ : parton cross sectioncs : speed of sound

S : transverse area (obtained by Glauber MC)

Transport Model Approach

C. Gombeaud and J.-Y. Ollitrault, PRC77, 054904 (2008)

event anisotropy at star

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