Zhangbu Xu, USTC 2008
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Jet Quenching at RHIC喷注淬灭
1. Basic properties of QCD relevant to us2. Fragmentation Function in e+e- and p+p 3. New Measurements at RHIC4. Compile RHIC data on jet chemistry5. Extract effective gluon Color Charge at RHIC6. Other unique features of QCD jet quenching7. Conclusion and Outlook
Zhangbu Xu, USTC 2008
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Fundamentals of QCD relevant to our fieldT.D. Lee, 1995
• Quark Confinement 夸克禁锢• Symmetry Breaking对称破缺
Gluons carry color-charge
Asymptotic Freedom
Zhangbu Xu, USTC 2008
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Color Factors
QCD : For SU(3) : Nc = 3 CA = 3, CF = 4/3
CF ~ strength of a gluon coupling to a quarkCA ~ strength of the gluon self coupling TF ~ strength of gluon splitting into a quark pair
CA/CF=9/4
s 藕合常数
Zhangbu Xu, USTC 2008
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Energy Loss and QCD
Experimentally observable (of Eloss) related to basic ingredientof QCD - Gauge Group through Color FactorsOr extracting an effective Color Factor
R. Baier et al., NPB 483 (1997) 291 M. Gyulassy et al., PRL 85 (2000) 5535 S. Wicks et al, nucl-th/0512076
hardparton
path length L
One mechanism of energy loss : Medium induced gluon radiation Eg
Eq~ 9/42
L<q>
CE s ^ C
Features of QCD energy loss• Color factor and coupling constant• Pathlength L2 dependence• Deadcone• Jet chemistry and Jet Conversion• Mach Cone
Zhangbu Xu, USTC 2008
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k
E
M
dP
k
dkkdCdP Fs
,
)/1()(
0
2220
022
022
22
1982: J. D. Bjoken: Fermilab-pub-82/59-THY Energy loss in elastic scattering1992/1995: X.-N. Wang, M. Gyulassy: PRL68(92) 148, PRD45 (92)844, NPB420(94)583, PRD51(95)3436 Energy loss is dominated by gluon radiation1995/1997: BDMPS (R. Baier, Yu. L. Dokshitzer, A. Mueller, S. Peigue, D.Schiff) :PLB345(95) 277, NPB478(96)577,NPB483(97)291,NPB484(97)265 Gluon multiple scattering and gluon radiation2000: GLV(M. Gyulassy, P. Levai, I. Vitev): PRL85(00)5535, NPB594(01)371 U. Wiedemann: NPB588(2000)303 Opacity expansion2001/2002: E. Wang, X.-N. Wang: PRL87(01)142301, PRL89(02)162301 Detailed Balance; Jet Tomography2001/2009Y. Dokshitzer & D. Kharzeev PLB 519(2001)199; S. Wicks et al, nucl-th/0512076
Zhangbu Xu, USTC 2008
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Consequence of CA/CF=9/4 in A+A
Other models: S. Wicks, I. Vitev, QM08
WHDG, arXiv:nucl-th/0512076
(AA
/p
p)
q/g~=9/4QGP 内高能部分子能损前后的空间分布
Zhangbu Xu, USTC 2008
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Processes in hadron-hadron collisions
PYTHIA provided by Adam Kocoloski
gg
gq
PDFParton 2->2 Fragmentation functions部分子分布函数 (PDF) 部分子作用截面碎裂函数
Zhangbu Xu, USTC 2008
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我们需要的量
1. 核子内部分子分布函数 (PDF)理论函数 (CTEQ6M) 拟合实验数据 (e+p)
2. 部分子作用截面和出射动量 二次展开的微挠色动力学 (NLO pQCD)
3. 碎裂函数 ( 喷注中强子的分布 )• 只取喷注中大动量的单个强子• 没有重建原始部分子• 理论函数 (DSS) 拟合实验数据 (e+e-,e+p,p+p)
4. 部分子在 QGP 中的能损机制
Zhangbu Xu, USTC 2008
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Fragmentation Functions
• Will these ingredients be sufficient for p+p collisions?
• How will p+p collisions provide additional information for our understanding of QCD and for model developments
• What will be modified in A+A collisions1. FF
2. Running of S
3. Effective Color Charge factor
喷注中强子的分布
Zhangbu Xu, USTC 2008
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PID at high-pT (where do we start?)
My talk: pT>5 GeV/c
Where it begins
Zhangbu Xu, USTC 2008
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Sources of high pT hadrons : quarks or gluons
At high pT range measured :Large gluon contribution (~ 90%) to produced baryonsSubstantial quark contribution (~ 40%) to produced
mesonsSTAR : PLB 637 (2006) 161 S. Albino et al, NPB 725 (2005) 181
Ng(i)/ (Ng(i) + Nq(i)); i = , K, p…
B. Mohanty (for STAR) nucl-ex/0705.9053L. Ruan (for STAR) nucl-ex/0701070 and WWND
Zhangbu Xu, USTC 2008
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Global Fit
Daniel de Florian, Rodolfo Sassot and Marco StratmannarXiv: 0707.1506 [hep-ph]; Phys.Rev.D76:074033,2007. DSS Fragmentation Functions –provided by W. Vogelsang
In principle, allow to separate quark-to-proton and anti-quark-to-proton fragmentation functions
The best constraint on the gluon fragmentation function Dg
p at large values of z currently available.
Zhangbu Xu, USTC 2008
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Extend Charged hadron spectra!
P. Fachini, QM08Y.C. Xu, DNP07
Zhangbu Xu, USTC 2008
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Comparison with pQCD
1. Clear flavor dependence 2. DSS NLO overpredicts pbar yield3. Best constraint on gluon/quark-to-proton
fragmentation functions at high z
Not all models are equal!
Zhangbu Xu, USTC 2008
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Quark vs gluon from hadron suppression
X.N. Wang and X.F. Guo, NPA 696(2001)788 T. Renk and K. Eskola, PRC 76 (2007)027901W. Liu, C.M. Ko, B.W. Zhang, nucl-th/0607047
PRL 97, 152301 (2006)STAR Preliminary
No sign of stronger gluon energy loss in p/ or p/p ratios
Need good understanding of how quarks and gluons turn into hadrons
STAR, B. MohantySTAR, P. Fachini
Curves: X-N. Wang et al PRC70(2004) 031901
质子和介子在 QGP 强子压底前后的比值
Zhangbu Xu, USTC 2008
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Thermal distribution among hadrons
• Statistical Mechanics describes the relative particle abundances
• This happens at the phase boundary (T=165+-10MeV)
STAR whitepaper
Low-pT integrated yields
强子的热统分布 : 温度和化学势
Zhangbu Xu, USTC 2008
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Jet Chemistry in p+p
pT>5 GeV/c 4<pT<5 GeV/c
高动量强子化学分布 强子来源和 QGP 作用下的变化
Zhangbu Xu, USTC 2008
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Effective Color Factor
a1Eq+b1dEg
----------------- = a2Eq+b2Eg
10%+90%C----------------- = RAA(p/) 60%+40%C
100%----------------- = RAA(e/) 60%+40%C
Simple Algebra:
Zhangbu Xu, USTC 2008
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Extract effective Color FactorsALEPH : ZPC 76 (1997) 1OPAL :EJPC 20 (2001) 601
SU(3) is the gauge group for QCD
S = 0.119
Zhangbu Xu, USTC 2008
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Convert to Effective CA/CF
hardparton
path length L
hardparton
path length L
20%+80%C----------------- = RAA(KS
0/) 60%+40%C
Conversion probability can be absorbed into C:
<= W. Liu, R.J. Fries, arXiv:0801.0453[nucl-th]
Zhangbu Xu, USTC 2008
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Constraints on Opacity (QGP 透明度 )
• Look at data in a quantitative way
• Geometry and evolution, dE/dx model
• How the gluon and quark compositions change with dE/dx?
• Different PID and global constraints on initial jet composition
PHENIX: WHDG
RAA (C,Eq,pT,FF)
Zhangbu Xu, USTC 2008
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Outlook - Energy Dependence
Similar Eloss for quarks and gluons
QCD type (color charge effect) Eloss
• Probing quark dominated jet production at lower energy to gluon dominated jet production at higher energy• Heavy-Flavor tag • +jet•pbar-pbar IAA (T. Renk)
Wang et al., PRC 58 (1998) 2321Wang et al., PRC 71 (2005) 014903
B. Mohanty, ISMD2007
Zhangbu Xu, USTC 2008
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Advantage of Di-hadron Correlations双强子关联
y (fm)
x (fm)Less surface bias
Single Di-hadron
y (fm)
x (fm)
Limited sensitivity of RAA to P(E,E)T. Renk, PRC 74 (2006) 034906
T. Renk and Eskola,hep-ph/0610059
Di-hadron correlations more robustprobes of initial density ~
H. Zhong et al., PRL 97 (2006) 252001
2IAA
2RAA
fmq 2GeV3.08.2~ˆ
Zhangbu Xu, USTC 2008
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光子无能损 , 可用来标定与其关联的喷注的原初能量
Beam
axis180°
BEMC
TPC
光子—强子关联 N
o tr
ack
wit
h p
>3G
eV/c
poi
nts
to
the
trig
ger
tow
er
0
2
Lead
ing
part
icle
Study the particles distribution
in fractional energyof ’s energy
Use Transverse Shower Profile for /0 identification.
Zhangbu Xu, USTC 2008
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光子—强子角关联的试验分布-rich sample versus 0-rich sample
oThe -rich sample has lower near-side yield than 0.
Zhangbu Xu, USTC 2008
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Eloss probability distribution : -hadron correlation
Provides constraints on Eloss probability distributions Possibly gives full accounting of jet energy loss
Jet
Prompt
1st measurement of away-side -h correlations Suppression similar level as inclusives in central collisions Note : Ejet = E
X.-N. Wang et alPRL 77(1996)231
Zhangbu Xu, USTC 2008
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Conclusions
QED FQHE(perfect fluid) Chern-Simon
• A large dataset extended to higher momentum with many identified particles in p+p and A+A collisions
• Effective gluon color charge factor<9/4
• Modeling flavor and color charge effectsRAA (C,Eq,pT,FF)
QCDsQGP (perfect Liquid) ?
Zhangbu Xu, USTC 2008
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作业题 I
计算喷注淬灭能损后 ( 反质子 / 介子 ) 的比值假设 p/in p+p, p 100% from gluon,
30% from gluon, 70% from quark
而且认为 SU(3) (pQCD) 可适用 1. >1
2. [0.25,1]
3. [0.01,0.25]
4. <0.01
Zhangbu Xu, USTC 2008
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作业题 II
2 )喷注淬灭能损后的能量跑哪儿去?3 )喷注淬灭能损( dE/dx) 和 带电粒子穿过探
测器的能损比较。
Zhangbu Xu, USTC 2008
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Nuclear Modification Factor
P. Fachini (STAR)
1. Same RAA for ,,2. Different RAA for
pbar,p,Ks, e(NPE)
Zhangbu Xu, USTC 2008
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Current Observations in STARAway side yield modification
What does these features reveal about the medium ?
Parton Eloss
High pT suppression
STAR : PLB 655 (2007) 104STAR : PRL 97 (2006) 152301STAR : PRL 91 (2003) 072304
Reappearance of di-jets
STAR : PRL 97 (2006) 162301
pTlp : 4 - 6 GeV/c
pTasoc : 2 GeV/c - pTlp
Away side shape modification
d+Au
Enhanced correlated yield at large on near side
Medium response
STAR : J. Putschke, QM2006STAR : M. J. Horner, QM2006
2.5 < pT
trig< 4 GeV/c
1< pT
assoc < 2.5 GeV/c
pTtrig=3-6 GeV/c,
2 GeV/c <pTassoc< pT
trig
Au+Au
STAR: PRL 95 (2005) 152301J.G. Ulery, QM 2005