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
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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
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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
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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
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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