Directed flow of identified particles from Au+Au Collisions at RHIC
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STARSTAR
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
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTAROutline
• Motivation• Data sample, Proton selections, & V0 reconstruction• Event plane reconstruction• v1 results• Discussion and Summary
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTAR
r
pt
Higher harmonics
rapidity
<px> or directed flow
)](cos[
)](cos[2121
1
2
3
3
rn
nrn
tt
nv
nvdydppNd
pdNdE
Anisotropic flow
Directed flow (v1)
Elliptic flow (v2)
Motivation
In the forward region +z, the leading participating nucleon will interact with many other nucleonsin the “almond”,they will go to +x direction.
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARMotivation
flowantiflow
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)
Anti-flow/3rd flow component, with QGP v1 flat at middle rapidity.
Directed flow (v1) and phase transition
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARProton & Antiproton Selection
Common cut:|Primary Vertex| < 30cmNo. Dedx Points > 10No. fit Points > 20No. fit Points/No. Max [0.52,1.05]Global DCA < 1.0cmnSigma [-2.5,2.5]
Proton: 0.4 < pT <1.0 (GeV/c) Antiproton: 0.15< pT <1.0 (GeV/c)
DataSet:62GeV Au+Au Minimum Bias 3M200GeV Au+Au Minimum Bias 7M STAR Preliminary
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARV0s 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 c
m– decay length > 6.0cm– daughter’s Tpc Hits > 15
0.48<mass<0.51 1.11<mass<1.12 1.11<mass<1.12
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTAR
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
Event Plane reconstruction
iiinnn
iiinnn
nwYnQ
nwXnQ
)sin()sin(
)cos()cos(
i
iw
)cos(
)sin(tan1 1
ii
i
ii
i
n nw
nw
n
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARCombined Event Plane
TPC FTPCFTPC ZDC-SMDZDC-SMD
Rapidity gapsReducednon-floweffects
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARFlattening Event Plane
E877 Collaboration, J. Bareeette et al, Phys.Rev.Lett.70,2996(1993)
Principle of shifting:Make corrections to the event planeangle itself, & flatten the event planedistribution. The corrected event plane angle is
FTPC Raw Phi distributionPrinciple of weighting:Due to detector acceptance effects, theevent plane distribution isn't isotropic. Tocorrect those effects, more weight is givento the particles that are detected at theplace where the least particle are detected.We are compensating for the “blind spots”of the FTPC.
FTPC weighed Psi distribution
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARSub-Event PlaneFTPC Event Plane distribution ZDCSMD Event Plane distribution
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTAR
• After the flattening of FTPC & ZDCSMD Full EP. The final event plane used is defined by the sum of
Where
• or
weight is from resolution
Combined Event Plane
ZDCSMDZDCSMDFTPCFTPC UweightUweight **
FTPCU
ZDCSMDU
combinedUZDCSMDFTPC UU
yyZDCSMDxxZDCSMDZDCSMD
yyFTPCxxFTPCFTPC
eQeQU
eQeQU
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARResolution 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.
STAR Preliminary STAR Preliminary
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARProton & Antiproton v1 vs.
Rapidity
Proton 0.4<pT<1.0 (GeV/c) Antiproton 0.15<pT<1.0 (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%.
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARProton & Antiproton v1 vs. Centrality
From the 10%-60%(central to peripheral)in 200GeV,v1(Anti-Proton) shows a weak centrality dependence.
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTAR
• For 200GeV, v1(Ks. & is less than 2%.• Ks v1 seems different in 200GeV & 62.4GeV • v1 is flat in the mid-rapidity in 200GeV & 62.4GeV with the errors v1
In 200GeV: Also is flat in the mid-rapidity with the errors In 62.4GeV: Seems to show a interested curve
• |y|<0.5: the Ks and seem in the same direction.• The error bar needs to be reduced.
Ks. & v1 vs. Rapidity
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTARSummary• The event plane resolution is enhanced by combining EP of F
TPC & ZDC-SMD with proper weight;• Au+Au at 62.4GeV
– Proton v1 is less than 1%.
– AntiProton v1 is less than 2%.
• Au+Au at 200GeV– Proton, AntiProton v1 is less than 0.5%.– Weak centrality dependence at 200GeV.
• Made an attempt to study directed flow of K0S & , .
To do list:• analysis run VII’s data (~60M MB events).
STARSTAR
Backup
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTAR
SMD is 8 horizontal slats & 7 vertical slats located at 1/3 of the depth of the ZDC
• 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
ZDC side view
Transverse plane of
ZDC
STAR ZDC-SMD
Scintillator slats of Shower Max Detector
第十届全国粒子物理学术会议 2008年 4月 26日 -4月 29 日 南 京
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STARSTAR
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