zhangbu xu, ustc 2008 1 jet quenching at rhic 喷注淬灭 1.basic properties of qcd relevant to us...

Zhangbu Xu, USTC 2008

1

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


2

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


3

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


4

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


5

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


6

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


7

Processes in hadron-hadron collisions

PYTHIA provided by Adam Kocoloski

gg

qq

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


8

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


9

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


10

PID at high-pT (where do we start?)

My talk: pT>5 GeV/c

Where it begins


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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


12

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.


13

Extend Charged hadron spectra!

P. Fachini, QM08Y.C. Xu, DNP07


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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!


15

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


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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


17

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


18

Effective Color Factor

a1Eq+b1dEg

----------------- = a2Eq+b2Eg

10%+90%C----------------- = RAA(p/) 60%+40%C

100%----------------- = RAA(e/) 60%+40%C

Simple Algebra:


19

Extract effective Color FactorsALEPH : ZPC 76 (1997) 1OPAL :EJPC 20 (2001) 601

SU(3) is the gauge group for QCD

S = 0.119


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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]


21

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)


22

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


23

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


24

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.


25

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.


26

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


27

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) ?


28

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


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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。


30

Nuclear Modification Factor

P. Fachini (STAR)

1. Same RAA for ,,2. Different RAA for

pbar,p,Ks, e(NPE)


31

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

zhangbu xu, ustc 2008 1 jet quenching at rhic 喷注淬灭 1.basic properties of qcd relevant to us...

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