PID v2 and v4 from Au+Au Collisions at √ sNN = 200 GeV at

RHIC

N. Li for the STAR Collaboration

Lawrence Berkeley National Laboratory, BerkeleyInstitute of Particle Physics, Wuhan, China

Outline

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•Motivation•Analysis•Results•Summary

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Motivation

Formation of QGP in high-energynuclear collisions:

• De-confinement• Collectivity• Local thermalization

Important questions

We study with dataset of highest statistics

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Anisotropy Parametersspatial space

anisotropy

momentum space

anisotropy

1

2

3

3

cos),(21

dd

d

2

1

pd

d

nrTn

TT

nypv

ypp

NNE

rn nv cos

Azimuthal correlation with the reaction plane.

Built up in the early stage, therefore supplies the early information of matter generated in the collision.

pQCD

ReCo & CoalescenceHydro

Motivation (cont.)

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Study the PID dependence of v2 and v4.

R. S. Bhalerao et.al PLB 627, 49; Borghini and Ollitrault, PLB 642, 227

Study Number-of-Quark scaling.

Range?

v4/v22 : a probe of ideal

hydro behavior.

STAR: Phys. Rev. C 77 (2008) 54901

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Anisotropy Parameter v2

Baryon and meson elliptic flow follow the number of quark ( Nq ) scaling.

Indicates that partonic flow builds up at RHIC.

STAR: Phys. Rev. C 77 (2008) 54901

How about the higher order anisotropic flow such as v4?

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Anisotropy Parameter v2 v4

Peter Kolb, PRC 68, 031902 STAR: Aihong Tang, Proc.24th Winter Workshop on Nuclear Dynamics

v4 : 4th harmonic

If system reaches local thermal equilibrium, according to ideal hydro dynamic calculation, v4/v2

2 approaches 0.5 at high pT region.

Directly related to the degree of thermalization of the medium.

Hydro, Boltzmann calculations: J. –Y. Ollitrault

Dataset and Cuts

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Tracks used for TPC event plane:

No. of fit hits > 15

No. of fit hits/No. of possible hits >0.52

0.1 < pT < 2.0 GeV/c

| η | < 1.0

• System: Au+Au collision

• Energy : sNN = 200 GeV

• Event sample : ~60 M events• Year: 2007• Pseudorapidity range:

TPC : -1.0 < η < 1FTPC : -4.0 < η < -2.5 (east) 2.5 < η < 4.0 (west)

Tracks used for FTPC event plane:

6 =< No. of fit hits < 12

No. of fit hits/No. of possible hits > 0.52

0.1 < pT < 2.0 GeV/c

2.5< | η | < 4.0

Event plane angle (Rad)

TPC Event Plane

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2nd harmonic event plane

Detector bias is removed by applying phi weights to the tracks.

Phi weights are generated by inverting the normalized phi distributions of detected tracks for a large event sample.

STAR preliminary (a)

STAR preliminary

(b)

(c)

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FTPC Event Plane1

' ( sin 2 cos 2 cos 2 sin 2 )n

n n n nn

J.Barrette et al. Phys. Rev. C56 (1997)3254

The event plane distribution is not flat after phi weight correction due to several acceptance effect of FTPC.

Add additional shift correction.

Large η gap is used to reduce the non-flow effect.

Phi weight + Shift

Phi weight

Event plane angle (Rad)

STAR preliminary

Invariant Mass Method

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Borghini et al. Phys. Rev. C70 (2006)4905

2

2 2

( ) cos(2( )

( ) ( ) ( )

Sig Bginv r

Sig Bginv inv inv

v m

Sig Bgv m v m m

Sig Bg Sig Bg

Assume bmamv invinvBg )(2

KS0

STAR preliminary

STAR preliminary

Pion and Proton Identification

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TPC: pi/K ~ 0.7 GeV/c pi+K/p ~1.1 GeV/c

pi/p ~ > 3GeV/c relativistic rise

Cuts used for identification:

No. of fit hits > 15

No. of fit hits/No. of possible hits >0.52

pT < 1 (GeV/c) -2 < nσπ (p) < 2pT > 2.5 (GeV/c) 0 < nσπ < 1 -1 < nσp < 0 M. Shao, et al., Nuclear Instruments

and Methods in Physics Research A 558 (2006) 419-429

pion purity: over 95% proton purity: 70%

The effect on proton v2 will be about 10%. )()(:

%70)(%30)(0

22

222

SKvKvAssume

pvKvv

Using Run 4 data result

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v2 {TPC} and v2 {FTPC}

v2(pT) have been measured for , p, KS0 and .

Non-flow effect reduced considerably by using the FTPC event plane.

STAR preliminary STAR preliminary

Au+Au 200GeV (minibias)

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Number of Quark (Nq) Scaling

STAR preliminary STAR preliminary

The number of quark scaling for , KS0 and holds

up to (mT – m)/nq ~ 1 GeV/c2.

Protons seem to deviate from the scaling at lower pT.

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v4 {TPC}

v4(pT) has been measured for , KS0 and .

The Nq scaling for v4 is observed at (mT - m)/nq < 1 GeV/c2, similar to that of v2.

STAR preliminary

STAR preliminary

STAR preliminary

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Test of Ideal Hydro Predictions

v4 /v22 is about 1 at pT ~ 2 GeV/c, larger than the value

0.5 expected from ideal fluid calculations.

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Summary FTPC event plane is used in STAR in order to reduce the non-flow effect. Run 7 high statistics data used in this analysis.

Proton and anti-proton seems to deviate from the number of quark scaling at (mT - m)/nq ~ 1 GeV/c2 .

The number of quark scaling has been observed for v4 at (mT - m)/nq < 1 GeV/c2.

Mesons and baryons (, KS0 and ) have similar v4/(v2)2

ratios. It is close to unity at pT > 1 GeV/c, higher than ideal hydrodynamic model predictions.

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BACK UP

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Number of Quark (Nq) Scaling

STAR preliminary

STAR preliminary