Transcript PPT

Anisotropic Flow at RHIC
Jiayun Chen
(for
Collaboration)
Institute of Particle Physics, HZNU, Wuhan, 430079, P.R.China
Brookhaven National Lab, Upton, NY,11973, USA
Outline
• Introduction and Motivation
• STAR Experiment
• Result and discussions
 Partonic Collectivity
 Ideal Hydrodynamic
 Indentified Particles’ (PID) Directed Flow
• Summary and outlook
Jiayun Chen for STAR Collaboration – QNP2009
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Azimuthal Anisotropy
pressure gradient  collective flow
Coordinate-Space
Anisotropy
interactions
Momentum-Space
Anisotropy
vn  cos n ,   tan 1 (
py
px
)
This is believed to be due to pressure gradients in the dense medium which
lead to collective motion.
Directed flow (v1) at forward rapidities describes the “side-splash”, the
foremost early collective motion of the system;
Elliptic flow (v2) demonstrated the development of collectivity
Provide insights into the EOS.
Jiayun Chen for STAR Collaboration – QNP2009
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STAR Detector
|η|<1.5
ZDC-SMD
2.5<|η|<4.0
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Partonic Collectivity
1) At low pT - mass dependence
2) At intermediate pT - clear difference between baryons and mesons
3) Hadrons with u-, d-, s-quarks show similar collectivity
Final word on partonic collectivity at RHIC!
PHENIX π and p: nucl-ex/0604011v1
NQ inspired fit: X. Dong et al. Phy. Let. B 597 (2004) 328-332
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Ideal Hydro Test (1)
Ideal hydro: P. Huovinen, private communication
Au+Au at 200 GeV
STAR preliminary
Phys. Rev. C 77 (2008) 54901
 Ideal hydro fails to reproduce the data.
Fluctuation of v2? Viscosity ? Incomplete thermalization ?
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Ideal Hydro Test (2)
Au+Au at 200 GeV
0-80%
Borghini & Ollitrault,
PLB 642 227 (2006)
 v4/v22 results suggest that ideal hydro limit is not reached.
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Stopping and space-momentum
correlation
space-momentum correlations, nucleus stopping
wiggle structure of v1(y) develops
R. Snellings, H. Sorge, S. Voloshin, F. Wang, N. Xu, PRL 84 (2000), 2803.
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Anti-flow/3rd flow component
flow
antiflow
Directed flow (v1) and phase transition,QGP
 v1(y) flat at mid-rapidity
Phys. Rev. C 61 (2000), 024909.
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PID Directed Flow v1
STAR preliminary
STAR preliminary
Proton
0.4<pT<1.0 (GeV/c)
Antiproton 0.4<pT<1.0 (GeV/c)
•
•
•
•
Pion
Kaon
0.15<pT<0.75 (GeV/c)
0.2<pT<0.6 (GeV/c)
First measurement of directed flow of antiprotons.
Proton directed flow "collapses".
Antiproton v1 has the same sign of that of pions - the collapse of proton v1
is not a mass effect.
Kaon has a smaller k/p cross section than that of pions, thus it suffers less
shadowing effect, yet we found negative v1 slope for both charged kaon
and kshort- consistent with "anti-flow" picture.
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Directed Flow v1
STAR preliminary
• Proton v1 slope is close to zero, if compared to others.
• The models with shadowing effects (RQMD) cannot explain the
v1 slope relative to that of pions.
Phys. Rev. Lett. 84 (2000) 2803;
Phys. Lett. B 526 (2002) 309–314;
Phys. Rev. C 71, 054905 (2005).
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Charged hadrons Directed Flow v1
STAR Preliminary
STAR Preliminary
• At mid-rapidity, all the results have comparable values. At forward
rapidity, the trend of v1 from low energy is different from high
energies. This is due to early longitudinal collision dynamics.
• V1 values lie on a common trend.
STAR : PRL 92 (2004) 062301
PRL101（2008）252301
NA49: PRC68(2003)034903
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Summary
 We found that proton v1 is "collapsed". By
comparing to anti-proton v1, such collapse is
found not due to mass effect. The comparison of
the ratio of proton v1 to that of pions, shows that
the shadowing effect alone cannot explain the
collapse of proton v1. Our finding is consistent
with “anti-flow” phenomena.
 V1 results from 9.2GeV are similar to those
obtained at SPS from collisions at similar
energies
 Partonic collectivity at RHIC done! Test of
local thermalization is the next step.
 Ideal hydro limit: v4/v22 data larger than ideal
hydro prediction.
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