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
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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
Na Li for STAR collaboration (BNL/IOPP)
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)
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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
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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
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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
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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)
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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
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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%
Na Li for STAR collaboration (BNL/IOPP)
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
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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
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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
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Backup
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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)