Production of meson, baryon and light nuclei in Au+Au collisions at RHIC
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Production of meson, baryon and light nucleiin Au+Au collisions at
RHIC
Haidong LiuUniv. of Science & Technology of
China
UC Davis, Aug 21, 2007 Haidong Liu 2
Outline
Motivation and introductions Detectors and techniques Results (RHIC run 4 AuAu 200
GeV) Conclusions & Discussions
UC Davis, Aug 21, 2007 Haidong Liu 3
Motivations
&
Introductions
UC Davis, Aug 21, 2007 Haidong Liu 4
Heavy-ion collisions at RHIC
Time
initial state
pre-equilibrium(high Q2 interactions)
QGP andhydrodynamic expansion
hadronization
freeze-out
Physics: 1) Parton distributions in nuclei 2) Initial conditions of the collision 3) A new state of matter – Quark-Gluon Plasma and its properties 4) Hadronization and freeze-out
UC Davis, Aug 21, 2007 Haidong Liu 5
Particles production
Pions and protons production Low pT – hydrodynamic Intermediate pT – partonic coalescence High pT – jet fragmentation
Light nuclei production Final-state coalescence
UC Davis, Aug 21, 2007 Haidong Liu 6
The success of hydrodynamic
At low pT, hydrodynamical models successfully reproduce the spectra and v2
STAR PRC.72 (2005) 014904
UC Davis, Aug 21, 2007 Haidong Liu 7
Coalescence at intermediate pT
STAR PRC.72 (2005) 014904
NQ scaling of v2 is a strong evidence
Coalescence
fragmenting parton:ph = z p, z<1
recombining partons:p1+p2=ph
UC Davis, Aug 21, 2007 Haidong Liu 8
STAR: Nucl. Phys. A 757 (2005) 102
The difference is not sensitive to the mass of the hadron, but rather depends on the number of valence quarks contained within it.
Coalescence at intermediate pT
UC Davis, Aug 21, 2007 Haidong Liu 9
High pT – from pp to AuAu
p+p collisions Parton Distribution Function
(derived from e-h scattering) pQCD (parton-parton interaction
cross section calculation) Fragmentation Function (derived
from e+e- collisions) Au+Au collisions
pp collisions + Nuclear effect
We understand pp collisions
UC Davis, Aug 21, 2007 Haidong Liu 10
Jet fragmentation in pp collisions
1. Improved FF reasonably reproduces data 2. pbar/ ~ 0.2 at RHIC, <<0.1 at low energy
pbar dominated by gluon FFPLB 637 (2006) 161
UC Davis, Aug 21, 2007 Haidong Liu 11
Jet quenching in Au+Au
STAR: Nucl. Phys. A 757 (2005) 102
Significant suppression of inclusive charged hadron is observed in central Au+Au collisions: Fragmentation+parton energy loss
UC Davis, Aug 21, 2007 Haidong Liu 12
X.N. Wang: PRC58(2321)1998.
Study the PID spectra and pbar/p ratios can help to further understand how the g/q jets interact with the medium
Parton energy loss in HIJING
HIJING calculation
UC Davis, Aug 21, 2007 Haidong Liu 13
pQCD: Color charge and flavor dependence of parton energy loss
dE/dx(c/b)<dE/dx(uds)< dE/dx(g)
S. Wicks et al., NPA 784(2007)426
UC Davis, Aug 21, 2007 Haidong Liu 14
The roles of energetic parton --- source of the meson/baryon production
(1)In LEP e+e- experiment, identified charged particle spectra can be measured from 2 kinds of hadronic Z decays: quark jets and gluon jets (DELPHI EPJC 17 (2000) 207)
(2) The anti-baryon phase space density can be accessed by measuring dbar/pbar
p
d
dydN
dydNyf
/
/
26
13
F.Q. Wang, N. Xu, PRC 61 021904 (2000)
UC Davis, Aug 21, 2007 Haidong Liu 15
Different mechanisms govern hadron formation in the different kinematic region
Different hadron species may have different sources
Those sources (g/q) may have different behavior when propagating the medium
To study those behaviors,PID in large pT range is required!
UC Davis, Aug 21, 2007 Haidong Liu 16
Light nuclei formation – final-state coalescence
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
Time
UC Davis, Aug 21, 2007 Haidong Liu 17
Final-state Coalescence
AppPd
dNEB
Pd
dNE
Pd
dNEB
Pd
dNE Ap
A
p
ppA
N
n
nn
Z
p
ppA
A
AA /
3333
11
A
A VB R. Scheibl, U. Heinz, PRC 59 1585 (1999)
•Coalescence parameters BA
•Light nuclei v2 – atomic mass number (A) scaling?(consequence of the final-state coalescence)
UC Davis, Aug 21, 2007 Haidong Liu 18
Detectors
&
Techniques
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STAR detectors: TPC & TOF
A new technology (TOF) ----Multi-gap Resistive Plate Chamber
1. Good timing resolution (<100ps)2. Two trays (TOFr+TOFp) for run 4,
acceptance~0.01, 120 trays (TOFr) in the future
Time Projection Chamber
1. Tracking2. Ionization energy loss (dE/dx)
UC Davis, Aug 21, 2007 Haidong Liu 20
PID – Hadrons
TPC
Relativistic rising of dE/dx
High pT
High performance of time resolution
Low & intermediate pT2.5<pT<3.0
PID up to 12 GeV/c
UC Davis, Aug 21, 2007 Haidong Liu 21
Light Nuclei Identification
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
UC Davis, Aug 21, 2007 Haidong Liu 22
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
UC Davis, Aug 21, 2007 Haidong Liu 23
Results
(Au+Au 200 GeV)
Pion and proton spectra: STAR Phys. Rev. Lett. 97 (2006) 152301
Nuclei spectra and v2: QM06 proceeding, J. Phys. G: Nucl. Part. Phys. 34 (2007) S1087-S1091
UC Davis, Aug 21, 2007 Haidong Liu 24
Pion & proton spectra
PID up to 12 GeV/c
STAR Collaboration PRL 97 (2006) 152301PAs: O. Barannikova, H. Liu, L. Ruan and Z. Xu
UC Davis, Aug 21, 2007 Haidong Liu 25
Nuclear Modification factor
In central Au+Au collisions:
At 1.5<pT<7 GeV/c, RCP(p+pbar) > RCP() , RCP(p+pbar) shows obvious decreasing trend.
At 4<pT<12 GeV/c, both and p are strongly suppressed. They approach to each other at about 0.3
Curve:I. Vitev, PLB 639 (2006) 38.pT
UC Davis, Aug 21, 2007 Haidong Liu 26
Anti-particle to particle ratios
1. -/+ are consistent with flat at unity in all pT, no significant centrality dependence.
2. pbar/p ratio: no significant centrality dependence, parton energy loss underpredicts the ratios (X.N. Wang, PRC 58 (2321) 1998).
UC Davis, Aug 21, 2007 Haidong Liu 27
Proton over pion ratios
1. The p(pbar)/ ratios in Au+Au collisions show strong centrality dependence.
2. In central Au+Au collisions, the p(pbar)/ ratios reach maximum value at pT~2-3 GeV/c, approach the corresponding ratios in p+p, d+Au collisions at pT>5 GeV/c.
3. In general, parton energy loss models underpredict p/ ratios. R.J. Fries, et al., Phys. Rev. Lett. 90 202303 (2003); R. C. Hwa, et al., Phys. Rev. C 70, 024905 (2004); DELPHI Collaboration, Eur. Phy. J. C 5, 585 (1998), Eur. Phy. J. C 17, 207 (2000).
UC Davis, Aug 21, 2007 Haidong Liu 28
Light Nuclei SpectraDeuteron Helium-3
QM06 proceeding: J. Phys. G: Nucl.Part. Phys. 34 (2007) S1087-S1091
UC Davis, Aug 21, 2007 Haidong Liu 29
Coalescence Parameters B2 & B3
•B2 & sqrt(B3) are consistent•Strong centrality dependence
11
A
A VB
(anti-)proton spectra: STAR Phys. Rev. Lett. 97, 152301 (2006)
A
p
ppA
A
AA Pd
dNEB
Pd
dNE
33
UC Davis, Aug 21, 2007 Haidong Liu 30
Coalescence Parameters B2 & B3
•Compare to pion HBT results•Beam energy dependence
11
A
A VB
A
p
ppA
A
AA Pd
dNEB
Pd
dNE
33
22
3
2 sidelongf RRV
HBT parameters: STAR Phys. Rev. C71 (2005) 044906
Assuming a Gaussian shape in all 3 dimensionsR. Scheibl et al.Phys.Rev.C59 (1999)1585
UC Davis, Aug 21, 2007 Haidong Liu 31
Scaled by A
Baryon v2 -- X.Dong et al, Phys. Lett. B597 (2004) 328-332
Light Nuclei v2
•This is the 1st helium-3 v2 measurement at RHIC
•Deuterons v2 follows A scaling within error bars
•Helium-3 v2 seems deviating from A scaling at higher pT
(need more statistics)
minBias
UC Davis, Aug 21, 2007 Haidong Liu 32
Low pT v2
The 1st observation of negative v2 at RHIC
No model can readily reproduce the data
dbar centrality bins: 0~12%, 10~20%, 20~40%, 40~80%pbar v2: STAR Phys. Rev. C72 (2005) 014904
d
BW parameters:F. Retiere, M. Lisa, Phys.Rev. C70 (2004) 044907
UC Davis, Aug 21, 2007 Haidong Liu 33
Accessing anti-baryon density by &
Source of anti-baryon production
pd /
H. Liu & Z. Xu, nucl-ex/0610035Submitted to PLB
UC Davis, Aug 21, 2007 Haidong Liu 34
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
p
d
dydN
dydNyf
/
/
26
13
F.Q. Wang, N. Xu, PRC 61 021904 (2000)
UC Davis, Aug 21, 2007 Haidong Liu 35
Anti-baryon Phase Space Density
STAR preliminary ARGUS e+e-
sqrt(s)=9.86() ggg highsqrt(s)=10 q+qbar low
UC Davis, Aug 21, 2007 Haidong Liu 36
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
UC Davis, Aug 21, 2007 Haidong Liu 37
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
UC Davis, Aug 21, 2007 Haidong Liu 38
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
UC Davis, Aug 21, 2007 Haidong Liu 39
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
UC Davis, Aug 21, 2007 Haidong Liu 40
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
UC Davis, Aug 21, 2007 Haidong Liu 41
Conclusions
&
Discussions
UC Davis, Aug 21, 2007 Haidong Liu 42
B/M enhancement at intermediate pT
The relative baryon enhancement is clearly observed in the p/pi ratios at intermediate pT, the similar behavior can also be seen in the /Ks
0 ratios. At the same pT region, the NQ scaling of v2 has also been observed. This can be explained by the parton coalescence phenomena.
STAR Nucl-ex/0601042
UC Davis, Aug 21, 2007 Haidong Liu 43
Freeze-out volumes
•B2 and B3 have strong centrality dependence, the system has larger freeze-out volumes in more central collisions.
•B2 and sqrt(B3) have similar values in different centrality collisions, which indicates that the deuteron and helium-3 have similar freeze-out volume.
•B2 has little beam energy dependence when sqrt(sNN)>20 GeV, which indicates that the freeze-out volume won’t change with the beam energy.
UC Davis, Aug 21, 2007 Haidong Liu 44
Light nuclei v2
•At intermediate pT, deuteron v2 follows A scaling within errors while helium-3 v2 seems deviates from this scaling, we need more statistics to draw further conclusion.
•At low pT, the dbar v2 is found to be negative. The BW model, which includes large radial flow scenario, also shows a negative flow prediction. But the BW model fails to reproduce our data since there is only mass input for light nuclei.
UC Davis, Aug 21, 2007 Haidong Liu 45
Color charge and flavor dependence of parton energy loss
High pT Rcp measurements: , p(pbar), e, , 0
pT
Nucl-ex/0607012 PRL 96 (2006) 202301
Rcp(RAA)~0.2 for all these particles!
UC Davis, Aug 21, 2007 Haidong Liu 46
Color charge and flavor dependence of parton energy loss
The partonic source:, , 0 – light quarks •p(pbar) – glouns •e – heavy quarks
pQCD calculations
dE/dx(c/b)<dE/dx(uds)< dE/dx(g)
S. Wicks et al., NPA 784(2007)426
Rcp(RAA)~0.2 for all these particles!???
UC Davis, Aug 21, 2007 Haidong Liu 47
Physics possible:g/q jets conversion in the medium
soft q(qbar)+
hard g
hard q(qbar)+
soft gCompton-like scattering:
W. Liu et al., nucl-th/0607047
A much larger cross-section is needed to explain our data
UC Davis, Aug 21, 2007 Haidong Liu 48
The future – a good time for discovery
Inv. Yield~Anti-3He : dbar : pbar 1 : 1K : 1M
In the RHIC upcoming high statistics AuAu runs, with STAR large acceptance detector TPC/TOF, we should try to search for anti-, which has never been observed before.
HeH
Hnp
33
3
And, there is also possible to discover Antihypernucleus
STAR Phys. Rev. Lett. 87 (2001) 262301
E864 Phys. Rev. Lett. 85 (2000) 2685
Thanks!
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