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