1. Jet Quenching and Its effects in Strong Interaction Matter
Enke Wang
(Institute of Particle Physics, Huazhong Normal University)
Jet Quenching
Modification of Hadron Fragmentation Function
Jet Tomography of Strong Interaction Matter
An explanation of heavy quark energy loss puzzle
Summary and Discussion

2. A-A collisions: Naturally provides jet and the QGP
I. Jet Quenching
Rutherford experiment a  atom discovery of nucleus
SLAC DIS experiment e  proton discovery of quarks
penetrating beam (jet)
absorption or scattering pattern
QGP
Hard Probes of Quark Matter:
A-A collisions: Naturally provides jet and the QGP
Jet (hard probe) created by parton scattering before QGP is formed
high transverse momentum
calculable in pQCD

3. 27 YEARS AGO

4. Brief History of Theoretical Research about Jet Quenching
1982: J. D. Bjoken: Fermilab-pub-82/59-THY
Energy loss in elastic scattering
1992/1995: X.-N. Wang, M. Gyulassy:
PRL68(92) 148, PRD45 (92)844, NPB420(94)583, PRD51(95)3436
Energy loss is dominated by gluon radiation
1995/1997: 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 radiation
2000: GLV(M. Gyulassy, P. Levai, I. Vitev): PRL85(00)5535, NPB594(01)371
U. Wiedemann: NPB588(2000)303
Opacity expansion
2001/2002: E. Wang, X.-N. Wang: PRL87(01)142301, PRL89(02)162301
Detailed Balance; Jet Tomography

5. Basic Idea for Jet Quenching
hadrons q
Leading particle suppressed
leading
particle suppressed
hadrons q
leading
particle
leading particle
p-p collision
A-A collision
At RHIC:
Hard/Semihard processes is important
High- Pt parton (jet)
Jet quenching
Jet production dominates particle yields
at high Pt
Suppression of high Pt hadron spectra

6. Jet quenching and Observation
hadrons q
Leading particle suppressed
leading
particle suppressed
Jet Quenching:
A-A collision
Modification of Fragmentation Function:
Particle Production:

7. Jet Quenching in QCD-based Model
G-W (M. Gyulassy, X. –N. Wang) Model:
Static Color-Screened Yukawa Potential

8. First Order in opacity Correction

9. First Order in opacity Correction
Induced gluon number distribution:
Non-Abelian LPM Effect
Medium-induced radiation intensity distribution:
Induced radiative energy loss:
QCD:
QED:

10. Higher order in Opacity
Reaction Operator Approach: (GLV)
Induced gluon number distribution:
Non-Abelian LPM Effect

11. Radiated Energy Loss vs. Opacity
First order in opacity correction is dominant!

12. Jet Quenching with Detailed Balance
E. Wang, X.-N. Wang, Phys. Rev. Lett. 87 (2001)
Temperature and Density QGP System
Gluon radiation: E loss
Net energy loss of jet:
Gluon absorption E absorption x p
Detailed Balance

13. Final-state Radiation
Energy loss induced by thermal medium: =
Net contribution: Energy gain
Stimulated emission increase E loss Thermal absorption decrease E loss

14. Energy Loss in First Order of Opacity
Energy loss induced by rescattering in thermal medium:
Take limit:
Zero Temperature Part: L 2
GLV Result
Temperature-dependent Part:
Energy gain

15. Numerical Result for Energy Loss
Intemediate large E, absorption is important
Energy dependence becomes strong
Very high energy E, net energy gain can be neglected

16. Parameterization of Jet Quenching with Detailed Balance Effect
Average parton energy loss in medium at formation time:
Energy loss parameter
proportional to the initial gluon density
Modified Fragmentation Function (FF)
(X. -N. Wang , PRC70(2004)031901)

17. Light Quark Energy Loss
PHENIX,
Nucl. Phys. A757 (2005) 184
Theoretical results from the light quark energy loss is consistent with the experimental data

18. II. Modification of Hadron Fragmentation Function
e-A DIS e-
Frag. Func.

19. Modified Fragmentation Function
Cold nuclear matter or hot QGP medium lead to the modification of fragmentation function

20. Twist-four calculation
X.-N. Wang, X. Guo, NPA696 (2001); PRL85 (2000) 3591 e-

21. Modified Frag. Function in Cold Nuclear Matter
Modified splitting functions
Two-parton correlation:
LPM

22. Modified Frag. Function in Cold Nuclear Matter
hadrons ph
parton E
are measured, and its QCD evolution
tested in e+e-, ep and pp collisions
Suppression of leading particles
Fragmentation function without medium effect:
Fragmentation function with medium effect:

23. Heavy Quark Energy Loss in Nuclear Medium
B. Zhang, E. Wang, X.-N. Wang, PRL93 (2004) ; NPA757 (2005) 493
Mass effects:
1) Formation time of gluon radiation time become shorter
LPM effect is significantly reduced for heavy quark
2) Induced gluon spectra from heavy quark is suppressed by
“dead cone” effect
Dead cone Suppresses gluon radiation amplitude at

24. Heavy Quark Energy Loss in Nuclear Medium
LPM Effect
1) Larg or small :
2) Larg or small :

25. Heavy Quark Energy Loss in Nuclear Medium
The dependence of the ratio between charm quark and light quark energy loss in a large nucleus

26. III. Jet Tomography of Strong Interaction Matter
E. Wang, X.-N. Wang, Phys. Rev. Lett. 89 (2002)
Jet Tomography in Cold Nuclear Matter:
Quark energy loss = energy carried by radiated gluon
Energy loss

27. Comparison with HERMES Data
, ,
HERMES Data: Eur. Phys. J. C20 (2001) 479

28. Expanding Hot Quark Gluon Medium
R. Baier et al

29. Initial Parton Density and Energy Loss
jet1
jet2
Initial energy loss in
a static medium with
density 15 2 A R t t =
0.1 fm
GeV/fm
Initial parton density (Energy loss ) is
15~30 times that in cold Au nuclei !

30. Comparison with STAR data
STAR, Phys. Rev. Lett. 91 (2003)

31. Tomography of Jet quenching in QGP Medium in NLO
1) Single jet  Single hadron spectra
2) Dijet  Hadron-triggered away-side hadron spectra
3) Gamma-jet  Photon-triggered away-side hadron spectra
Single jet Dijet Gamma-jet

32. Surface Emission of Single Hadron Production
H. Zhang, J. F. Owens, E. Wang and X.-N. Wang , Phys. Rev. Lett. 98 (2007) y x
Single hadron
parton jet
emission surface
corona thickness
completely suppressed

33. Surface Emission + Punch-through jet in Dihadron Productiony x
triggered hadron
associated hadron
partonic di-jet
tangential
punch-through jets
25% left
Color strength = dihadron yield from partons in the square

34. Prediction at LHC At LHC single hadron dihadron Surface emission bias
punch-jets

35. Gamma-jet by NLO pQCD parton model
LO (tree level): NLO corrections: (e.g. 23)
hadrons with transverse momentum may be larger than that of the photon
Fix triger:

36. Gamma-Hadron Suppressions Factor
NLO radiative corrections lead to hadrons with z_T>1, surface emission,
z_T<0.6, volume emission, more sensitive to \eps_0
0.6<z_T<1.4, competition of two mechanisms of hadron emssions.
Similarity in value between I_AA for dihadron and Gam-hadron.
H.Z. Zhang, J.F. Owens, E. Wang and X.-N. Wang , PRL 103 (2009)

37. Tomography of surface and volume emissions
The spatial transverse distribution of the initial Gama-jet production vertexes that contribute to the Gama-hadron pairs with given values of z_T.
The color strength : Gama-hadron yield
Projections of the contour plots onto y-axes .
At large z_T, jet emissions in the
outer corona, no energy loss.
At small z_T, jets emisions near the
center of the medium, energy loss.

38. IV. An explanation of heavy quark energy loss puzzle
QGP system is not static, it is a expanding system
Reaction
plane Y X
Flow
QED:
Static Charge: Coulomb electric field
Moving Charge: electric and magnetic field
QCD:
Static Target: static color-electric field
Moving Target: color-electric and color-magnetic field

39. Puzzle for Heavy Quark Energy Loss
B. Zhang, E. Wang, X.-N. Wang,
PRL93 (2004)
Y. Dokshitzer & D. Kharzeev
PLB 519(2001)199
Heavy quark has less dE/dx due to suppression of small angle gluon radiation
“Dead Cone” effect
J. Adams et. al,
PRL 91(2003)072304
M. Djordjevic, et. al.
PRL 94(2005)112301

40. No Significant Difference Between Heavy Quark Jet and Light Quark Jet
Charged hadrons from
Light quark fragmentation
Non-photonic electrons
from heavy quark decays
STAR

41. Interaction Potential with Flow
system fixed at target parton:
Static potential
system for observer:
Lorentz boost from system

42. New Model Potential with Flow
Four-vector potential :
The features of the new potential:
Collective flow produces a color-magnetic field
2) non-zero energy transfor:

43. Dead Cone Reduce Significantly with Flow
Reason: Collective flow changes the poles of the propagator

44. Energy Loss vs. Flow Velocity

45. Average Flow Velocity and Effective Average Energy Loss
3D ideal Hydrodynamic simulation for 0-10% central events of Au-Au collisions at RHIC energy:
Effective Average Energy Loss:

46. Numerical Results of Effective Average Energy Loss
3D ideal Hydrodynamic simulation for 0-10% central events of Au-Au collisions at RHIC energy

47. V. Summary and Discussion
Jet can be used as a hard probe to explore the QGP.
Jet quenching lead to modification of hadron fragmentation function, which result in the suppression of high transverse momentum spectra observed in experiment.
Different tomography picture of the QGP for single jet, dijet and gamma-jet: surface vs. volume emission.
New potential for the interaction of a hard jet with the parton target has been derived. Collective flow reduce significantly the dead cone from mass effect for heavy quark jet. Heavy quark energy loss increase obviously in the presence of collective flow. An explanation of heavy quark loss puzzle is given in the framework of jet quenching theory.

48. Discussion
1) Dihadron azimuthal correlations in head-on collisions in AMPT :
Talk this afternoon by Qingjun Liu
2) Multiple parton scattering and modified fragmentation
function in medium :
Talk this afternoon by Weitian Deng
3) Gamma-jet tomography of high-energy nuclear collisions in NLO pQCD :
Talk this afternoon by Hangzhong Zhang

49. Thank You