Directed flow of identified particles from Au Au Collisions at RHIC

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Directed flow of identified particles from AuAu
Collisions at RHIC

• Jiayun Chen
• (for the STAR Collaboration)
• Institute of Particle Physics, Wuhan, P.R. China

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Outline

• Motivation
• Data sample,
• Proton selections,
• V0 reconstruction
• Event plane reconstruction
• v1 results
• Discussion and Summary

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Motivation
pt
Directed flow (v1)
Anisotropic flow
Elliptic flow (v2)
Higher harmonics
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Motivation
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)
024909. L.P. Csernai, D. Roehrich
PLB 458, 454 (1999) M.Bleicher and
H.Stocker, PLB 526,309(2002)
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Proton Antiproton Selection

• Common cut
• Primary Vertex lt 30cm
• No. Dedx Points gt 10
• No. fit Points gt 20
• No. fit Points/No. Max 0.52,1.05
• Global DCA lt 1.0cm
• nSigma -2.5,2.5
• Proton 0.4 lt pT lt1.0 (GeV/c)
• Antiproton 0.15lt pT lt1.0 (GeV/c)
• DataSet
• 62GeV AuAu Minimum Bias 3M
• 200GeV AuAu Minimum Bias 7M

STAR Preliminary
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V0s reconstruction

• cuts
• Distance of closest approach(DCA)
• between daughters
  lt 0.8cm
• DCA of V0 to Primary Vertex (PV) lt 0.5cm
• Daugters DCA to PV gt
  0.8 cm
• decay length
  gt 6.0cm
• daughters Tpc Hits
  gt 15

1.11ltmasslt1.12
0.48ltmasslt0.51
1.11ltmasslt1.12
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Event Plane reconstruction

• the event plane vector and the event
  plane angle from the nth harmonic of
  the particles azimuthal distribution are defined
  by the equations
• -- the azimuthal angle of the ith
  particle in the event plane determination
• -- weights

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Combined Event Plane
Reduced non-flow effects
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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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Sub-Event Plane
FTPC Event Plane distribution
ZDCSMD Event Plane distribution
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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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Resolution of FTPC,ZDCSMD,Combined

• The event plane resolution(62 GeV) is enhanced by
  combining EP of FTPC ZDC-SMD with proper
  weight.
• 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.

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Proton Antiproton v1 vs. Rapidity
Proton 0.4ltpTlt1.0 (GeV/c)
Antiproton 0.15ltpTlt1.0 (GeV/c)

• For 62.4GeV, we use combined reaction plane
  while for 200GeV, use ZDC-SMDs as reaction
  plane.
• Proton and Anti-Proton v1
• For 62.4GeV Proton v1 is less than
  1,antiproton v1 is less than 2.
• For 200GeV Proton anit-Proton v1 is less
  than 0.5.

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Proton Antiproton v1 vs. Centrality

• From the 10-60(central to peripheral)in
  200GeV,v1(Anti-Proton) shows a weak centrality
  dependence.

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Ks. L ?L v1 vs. Rapidity

• For 200GeV, v1(Ks. L ?L) is less than 2.
• Ks v1 seems different in 200GeV 62.4GeV
• L v1 is flat in the mid-rapidity in 200GeV
  62.4GeV with the errors
• ?L v1
• In 200GeV Also is flat in the mid-rapidity with
  the errors
• In 62.4GeV Seems to show a interested curve
• ylt0.5 the Ks and ?L seem in the same
  direction.
• The error bar needs to be reduced.

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Summary

• The event plane resolution is enhanced by
  combining EP of FTPC ZDC-SMD with proper
  weight
• AuAu at 62.4GeV
• Proton v1 is less than 1.
• AntiProton v1 is less than 2.
• AuAu at 200GeV
• Proton, AntiProton v1 is less than 0.5.
• Weak centrality dependence at 200GeV.
• Made an attempt to study directed flow of K0S
  L, ?L.
• To do list
• analysis run VIIs data (60M MB events).

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Backup
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STAR ZDC-SMD
ZDC side view
SMD is 8 horizontal slats 7 vertical slats
located at 1/3 of the depth of the ZDC
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

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