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. ChinaBrookhaven National Lab.

SQM07 June. 24. 2

STARSTAROutline

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

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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

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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

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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 200GeV Au+Au Minimum Bias STAR Preliminary

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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 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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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

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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

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STARSTAREvent PlaneFTPC Event Plane distribution ZDCSMD Event Plane distribution

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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

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STARSTARResolution of FTPC,ZDCSMD,{FTPC,ZDCSMD}(62GeV Au+Au)

The event plane resolution is enhanced by combining EP of FTPC & ZDC-SMD with proper weight.

STAR Preliminary

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STARSTARProton & Antiproton v1 vs. Rapidity(62GeV)

Proton 0.4<pT<1.0 (GeV/c) v1=ay dv1/dy = -0.4± 1.1 Antiproton 0.15<pT<1.0 (GeV/c) v1=ay dv1/dy = 1.3± 1.5

30%-60%

with combined RP

STAR Preliminary

• Proton v1 is less than 1%,

• Antiproton v1 is less than 2%.

30%-60% STAR Preliminary

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STARSTARResolution 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.

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STARSTARProton & Antiproton v1 vs. Rapidity(200GeV)

Proton 0.4<pT<1.0 (GeV/c) v1=ay dv1/dy = -1.9± 0.8 Antiproton 0.15<pT<1.0 (GeV/c) v1=ay dv1/dy = -0.6± -1.0

with {ZDC-SMDs} RP

STAR Preliminary30%-60%

• Proton v1 is less than 1%,

• Antiproton v1 is less than 2%.

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STARSTARProton & Antiproton v1 vs. Centrality

• v1(proton & antiproton) at 62GeV have weak centrality dependence.

STAR PreliminarySTAR Preliminary

62GeV combined RP 200GeV ZDC-SMDs RP

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STARSTAR

v1=ay dv1/dy =-3.2±1.7

Ks v1 vs. Rapidity(62GeV)STAR Preliminary

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STARSTAR

Work in progress.

& v1 vs. Rapidity(62GeV)STAR Preliminary STAR Preliminary

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STARSTARSummary• The event plane resolution is enhanced by combini

ng 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 & ,

.• Looking forward to analyzing run VII’s data (~60M

MB events).

STARSTAR

Backup

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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

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STARSTARMotivationRQMD v2.4

R.Snellings, H.Sorge, S.Voloshin, F.Wang, N. Xu, PRL (84) 2803(2000)

Positive space-momentum correlation, no QGP necessary v1 wiggle.

Directed flow (v1) and baryon stopping

SQM07 June. 24. 22

STARSTAR Motivation• freeze-out of multi-stra

nge 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)

(GeV

)

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STARSTAR