Yields & elliptic flow of and in Au+Au collisions at

Haidong Liu University of Science & Technology of

China

For the STAR Collaboration

)(dd

GeVsNN 200)( 33 HeHe

Quark Matter 2006, Shanghai Haidong Liu 2

Outline Introduction & motivation Measurements

Analysis technique Results – spectra; B2 & B3; v2

Discussion: anti-baryon phase space density

Summary

Quark Matter 2006, Shanghai Haidong Liu 3

Introduction (I)

ChemicalFreeze-out

ThermalFreeze-out

InitialCollisions “QGP”

“De-confinement”Hadronization Late stagescattering

Due to the small binding energy, light nuclei cannot survive before thermal freeze-out. Therefore, light nuclei production and their elliptic flow are sensitive to the freeze-out conditions, such as temperature, particle density, local correlation volume and collective motion.

Henppdnp 3

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Introduction (II)(a) Coalescence parameter BA

AppPd

dNEB

PddNE

PddN

EBPd

dNE Ap

A

p

ppA

N

n

nn

Z

p

ppA

A

AA /3333

11

A

A VB See some detailed

discussions at:R. Scheibl, U. Heinz, PRC 59 1585 (1999)(b) Access to baryon phase space

density

p

d

dydNdydN

yf//

261

3

F.Q. Wang, N. Xu, PRC 61 021904 (2000)

(A: atomic mass number)

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Introduction (III)Coalescence at parton level hadrons group by their types rather than their

mass at intermediate pT

(i)Rcp groups by hadron type (ii)v2 follows NQ scaling

Coalescence at nuclear level Does the light nuclei v2 follow A scaling?

STAR Nucl. Phys. A 757 (2005) 102

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A new technology (TOF) ----Multi-gap Resistive Plate Chamber

1. Good timing resolution, (, K) ~1.6 GeV/c, p ~ 3 GeV/c

2. 1/100 acceptance (TOFrp) for now, full barrel in the future

Time Projection Chamber

1. Tracking2. Ionization energy loss (dE/dx)3. Coverage -1<<1

STAR Detectors: TPC & TOF

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Particles Identification

STAR preliminary PID Range (GeV/c):

6p2 :HeHe

3p0.2 :d

4p1 :d

T33

T

T

TOF

)expdEdx

measuredEdxLog(Z

)( 33 HeHe

GeV/c 6p2 T

GeV/c 1p7.0 T GeV/c 3p2.5 T

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Light Nuclei Spectra

STAR preliminary STAR preliminary

Deuteron Helium-3

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Coalescence Parameters B2 & B3

•B2 & sqrt(B3) are consistent•Strong centrality dependence

11

A

A VB

STAR preliminary STAR preliminary

(anti-)proton spectra: STAR Phys. Rev. Lett. 97, 152301 (2006)

A

p

ppA

A

AA Pd

dNEB

PddNE

33

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Coalescence Parameters B2 & B3

•Compare to pion HBT results•Beam energy dependence

11

A

A VB

STAR preliminary

A

p

ppA

A

AA Pd

dNEB

PddNE

33

223

2 sidelongf RRV

HBT parameters: STAR Phys. Rev. C71 (2005) 044906

STAR preliminary

Assuming a Gaussian shape in all 3 dimensionsR. Scheibl et al.Phys.Rev.C59 (1999)1585

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STAR preliminary

Scaled by A

Baryon v2 -- X.Dong et al, Phys. Lett. B597 (2004) 328-332

Light Nuclei Elliptic Flow v2STAR preliminary •This is the 1st helium-3 v2

measurement at RHIC•Helium-3 v2 seems deviating from A scaling at higher pT (need more statistics)

xy

px

py

Time

•Coalescence possibility has been weaken when fireball expanded•X-direction expands faster than y-direction

Non-centralcollision

xy

minBias

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Low pT v2

STAR preliminary

The 1st observation of negative v2 at RHIC

It is expected that heavy particles have negative v2 at low pT

22

22

2yx

yx

pppp

v

pT

X-direction

Y-direction

positive v2negative v2

pT0Heavy particles have large pT0, so it’s easier to observe negative v2 for heavy particles

dbar centrality bins: 0~12%, 10~20%, 20~40%, 40~80%pbar v2: STAR Phys. Rev. C72 (2005) 014904

d

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In nucleus+nuclues collisions, the anti-baryon density increases with beam energy and reaches a plateau above ISR beam energy regardless the beam species (pp, pA, AA).It can be fitted to a thermal model : ppTmpd B //exp/

Anti-baryon Phase Space DensitySTAR preliminary

H.D. Liu, Z. Xu nucl-ex/0610035Submitted to PLB

p

d

dydNdydN

yf//

261

3

F.Q. Wang, N. Xu, PRC 61 021904 (2000)

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Anti-baryon Phase Space Density

STAR preliminary ARGUS e+e-

sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar low

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Anti-baryon Phase Space Density

ARGUS e+e-

sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar lowALEPH(LEP) e+e-

sqrt(s)=91(Z) q+qbar low

STAR preliminary

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Anti-baryon Phase Space Density

ARGUS e+e-

sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar lowALEPH(LEP) e+e-

sqrt(s)=91(Z) q+qbar lowAGS, SPS, RHIC, ISR, Tevatronnucleus+nucleus (AA, pA, pp, p+pbar)sqrt(sNN)>50 q+g, qbar+g highsqrt(sNN)<20 q+g, q+q low

STAR preliminary

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Anti-baryon Phase Space Density

ARGUS e+e-

sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar lowALEPH(LEP) e+e-

sqrt(s)=91(Z) q+qbar lowAGS, SPS, RHIC, ISR, Tevatronnucleus+nucleus (AA, pA, pp, p+pbar)sqrt(sNN)>50 q+g, qbar+g highsqrt(sNN)<20 q+g, q+q lowH1(HERA) pWp =200 qqbar+g high

STAR preliminary

Quark Matter 2006, Shanghai Haidong Liu 18

ARGUS e+e-

sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar lowALEPH(LEP) e+e-

sqrt(s)=91(Z) q+qbar lowAGS, SPS, RHIC, ISR, Tevatronnucleus+nucleus (AA, pA, pp, p+pbar)sqrt(sNN)>50 q+g, qbar+g highsqrt(sNN)<20 q+g, q+q lowH1(HERA) pWp =200 qqbar+g high

In e+e-, the density through qqbar processes is a factor of strong coupling constant less than that through ggg processes (s=0.12)

(q+qbar->q+qbar+g)

s

STAR preliminary

Anti-baryon Phase Space Density

H. Liu, Z. Xu nucl-ex/0610035

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Where does (anti-)baryon come from?

In short, anti-baryon phase space density from collisions involving a gluon is much higher than those without gluons

Conclusions:

(1) Collisions which contain ggg, qbar+g or qqbar+g processes have higher anti-baryon phase space density

(2) Processes q+qbar create few anti-baryons

(3) Processes q+g create few anti-baryons at low energy – energy too low?

STAR preliminary

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Summary (I) With STAR TPC+TOF, spectra and elliptic flow

parameter v2 of and have been measured.

Coalescence parameters The correlation volume is larger in more central

collisions. For beam energy > 20 GeV, B2 doesn’t change

with collisions energy indicating a constant correlation volume at freeze-out.

In different centrality collisions, the correlation volumes are proportional to the pion HBT results.

)(dd )( 33 HeHe

32 ~ BB

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Summary (II) v2 measurements

Light nuclei v2 has been measured The 1st negative v2 at RHIC has been

observed (anti-deuteron, pT<0.7)

Anti-baryon phase space density In nucleus+nucleus collisions, the anti-

baryon density can be fitted to a thermal model independent of the beam species

Gluon interactions enhance anti-baryon production

Thanks!

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Backup slides

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STAR preliminary

TOF

)expdEdx

measuredEdxLog(Z

)( 33 HeHe

GeV/c 6p2 T

GeV/c 1p7.0 T GeV/c 3p2.5 T

Quark Matter 2006, Shanghai Haidong Liu 24

H.D. Liu, Z. Xu nucl-ex/0610035Submitted to PLB

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PID – Hadrons

TPC

M. Shao et al., NIMA 558, (419) 2006

STAR preliminary

STAR preliminary

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Pion & proton Spectra

STAR preliminarynucl-ex/0606003

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Feed-down correction for (anti-)protons

Method 1: Primordial protons and the protons come from weak decays have different DCA distribution

Primordial (MC) From decay (MC)

Method 2: From the measurements of and spectra, we can estimate the FD contribution STAR preliminary

Quark Matter 2006, Shanghai Haidong Liu 28

dbar centrality bins: 0~12%, 10~20%, 20~40%, 40~80%pbar v2: STAR Phys. Rev. C72 (2005) 014904

BW parameters: F. Retiere, M. Lisa, Phys.Rev. C70 (2004) 044907