1. Directed flow of identified particles from Au+Au Collisions at RHIC
Jiayun Chen
(for the STAR Collaboration)
Institute of Particle Physics, Wuhan, P.R. China
Brookhaven National Lab.

2. Outline Motivation Data sample, Proton selections, & V0 reconstruction
Event plane reconstruction
v1 results
Discussion and Summary
SQM07 June. 24.

3. Motivation pt Directed flow (v1) Anisotropic flow Elliptic flow (v2)
Higher harmonics
rapidity
<px> or directed flow
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4. Motivation Directed flow (v1) and phase transition
antiflow
Anti-flow/3rd flow component, with QGP  v1 flat at middle rapidity.
Directed flow (v1) and phase transition
Brachmann, Soff, Dumitru, et. al. , PRC 61 (2000)
L.P. Csernai, D. Roehrich PLB 458, 454 (1999)
M.Bleicher and H.Stocker, PLB 526,309(2002)
SQM07 June. 24.

5. Proton & Antiproton Selection
Common cut:
|Primary Vertex| < 30cm
No. Dedx Points > 10
No. fit Points > 20
No. fit Points/No. Max [0.52,1.05]
Global DCA < 1.0cm
nSigma [-2.5,2.5]
Proton: < pT <1.0 (GeV/c)
Antiproton: 0.15< pT <1.0 (GeV/c)
DataSet:
62GeV Au+Au Minimum Bias
200GeV Au+Au Minimum Bias
STAR Preliminary
SQM07 June. 24.

6. V0s reconstruction cuts: Distance of closest approach(DCA)
between daughters < 0.8cm
DCA of V0 to Primary Vertex (PV) < 0.5cm
Daugter’s DCA to PV > 0.8 cm
decay length > 6.0cm
daughter’s Tpc Hits > 15
0.48<mass<0.51
1.11<mass<1.12
1.11<mass<1.12
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7. Event Plane reconstruction
the event plane vector and the event plane angle from the nth harmonic of the particle’s azimuthal distribution are defined by the equations:
-- the azimuthal angle of the ith particle in the event plane determination
-- weights
SQM07 June. 24.

8. Flattening Event Plane
FTPC Raw Phi distribution
Principle of shifting:
Make corrections to the event plane
angle itself, & flatten the event plane
distribution.
The corrected event plane angle is
FTPC weighed Psi distribution
E877 Collaboration, J. Bareeette et al, Phys.Rev.Lett.70,2996(1993)
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9. Event Plane FTPC Event Plane distribution
ZDCSMD Event Plane distribution
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10. Combined Event Plane After the flattening of YFTPC & YZDCSMD Full EP.
The final event plane used is defined by the sum of
Where or
weight is from resolution
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11. Resolution of FTPC,ZDCSMD,{FTPC,ZDCSMD}(62GeV Au+Au)
STAR Preliminary
The event plane resolution is enhanced by
combining EP of FTPC & ZDC-SMD with proper weight.
SQM07 June. 24.

12. Proton & Antiproton v1 vs. Rapidity(62GeV)
STAR Preliminary
STAR Preliminary
30%-60%
30%-60% y
with combined RP
Proton <pT<1.0 (GeV/c)
v1=ay dv1/dy = -0.4± 1.1
Antiproton <pT<1.0 (GeV/c)
v1=ay dv1/dy = 1.3± 1.5
Proton v1 is less than 1%,
Antiproton v1 is less than 2%.
SQM07 June. 24.

13. Resolution of FTPC,ZDCSMD,{FTPC,ZDCSMD}(200GeV Au+Au)
Because the directed flow moves to larger pseudo-rapidity at the higher beam energy, the FTPC is less useful.
no obvious improvement for combined event plane at 200GeV.
SQM07 June. 24.

14. Proton & Antiproton v1 vs. Rapidity(200GeV)
30%-60%
STAR Preliminary
with {ZDC-SMDs} RP
Proton <pT<1.0 (GeV/c)
v1=ay dv1/dy = -1.9± 0.8
Antiproton <pT<1.0 (GeV/c)
v1=ay dv1/dy = -0.6± -1.0
Proton v1 is less than 1%,
Antiproton v1 is less than 2%.
SQM07 June. 24.

15. Proton & Antiproton v1 vs. Centrality
STAR Preliminary
STAR Preliminary
62GeV combined RP
200GeV ZDC-SMDs RP
v1(proton & antiproton) at 62GeV have weak centrality dependence.
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16. Ks v1 vs. Rapidity(62GeV) v1=ay dv1/dy =-3.2±1.7 STAR Preliminary
SQM07 June. 24.

17. L & L v1 vs. Rapidity(62GeV)
STAR Preliminary
STAR Preliminary
Work in progress.
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18. Summary
The event plane resolution is enhanced by combining EP of FTPC & ZDC-SMD with proper weight;
Au+Au at 62.4GeV & 200GeV
Proton v1 is less than 1%.
AntiProton v1 is less than 2%.
Weak centrality dependence at 62GeV.
Made an attempt to study directed flow of K0S & L, L.
Looking forward to analyzing run VII’s data (~60M MB events).
SQM07 June. 24.

19. Backup

20. Transverse plane of ZDC
STAR ZDC-SMD
SMD is 8 horizontal slats & 7 vertical slats located at 1/3 of the depth of the ZDC
ZDC side view
Transverse plane of ZDC
Scintillator slats of Shower Max Detector
New knowledge of the direction of the impact parameter vector
Minimal, if any, non-flow effects
Worse resolution than from TPC, but that disadvantage is minor
SQM07 June. 24.

21. Motivation Directed flow (v1) and baryon stopping
RQMD v2.4
Positive space-momentum correlation, no QGP necessary  v1 wiggle.
Directed flow (v1) and baryon stopping
R.Snellings, H.Sorge, S.Voloshin, F.Wang, N. Xu, PRL (84) 2803(2000)
SQM07 June. 24.

22. Motivation freeze-out of multi-strange hadrons
(GeV)
freeze-out of multi-strange hadrons
- at higher
temperature Tfo
- with lower
collective
velocity T
less interaction of strange hadrons with non-strange hadrons
sensitivity to the early, partonic stage
Nucl. Phys. A757, 102 (2005)
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23. SQM07 June. 24.