1. Modification of Fragmentation Function in Strong Interacting Medium
Enke Wang
(Institute of Particle Physics, Huazhong Normal University)
Introduction
Modification of Frag. Func. in Cold Nucleus
Modification of Frag. Func. in QGP Medium
Summary
Collaborators: X.-N. Wang, B.-W. Zhang

2. A-A collisions: Naturally provides jet and the QGP
I. Introduction
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. Jet quenching and Observation
hadrons q
Leading particle suppressed
leading
particle suppressed
Jet Quenching:
A-A collision
Modification of Fragmentation Function:
Particle Production:

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

5. Heavy quark energy loss: Early Expectations
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

6. 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

7. Question: Heavy Quark Energy Loss?
Theoretical Calculation
Energy loss fraction
How Reasonable?

8. II. Modification of Frag. Func. in Cold Nucleus
e-A DIS: e-
Frag. Func.

9. Modified Fragmentation Function
X.-N. Wang, X. Guo, NPA696 (2001); PRL85 (2000) 3591
Fragmentation function in vacuum
Modification term

10. Modified Frag. Function in Cold Nuclear Medium
Modified splitting functions
Two-parton correlation:
LPM

11. Rescaling of Modified Fragmentation Function
Solid curve:
Dashed curve:

12. Comparison with HERMES Data
, ,
E. Wang, X.-N. Wang, Phys. Rev. Lett. 89 (2002)

13. Heavy Quark Energy Loss in Cold Nucleus
B. Zhang, E. Wang, X.-N. Wang, PRL93 (2004) ; NPA757 (2005) 493
Mass effects:
1) Formation time of gluon radiation 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

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

15. III. Modification of Frag. Func. in QGP Mediumk k
Cold Nucleus Medium
QGP Medium

16. Same Framework for Light and Heavy Quark
Light quark:
Heavy quark:
Peterson form

17. Generalized Jet Transport Parameter
Unintegrated gluon distribution function:
Average tranverse momentum broading:
averaged transverse momentum transfer
squared per unit distance

18. Jet Energy Loss
LPM effect

19. Modified Frag. Function in QGP Medium
Modified splitting functions
Parameters:

20. Modification of Frag. Func. for light quark in QGP
can be approached by z
Solid Curve:
Dashed curve:

21. Modified Frag. Func. for heavy quark in QGP
c quark:
vacuum
medium
rescaling
medium/vacuum
rescaling/vacuum
E=10GeV
E=50GeV z
can be approached by

22. b quark: can be approached by E=10GeV E=50GeV z z vacuum medium
rescaling
medium/vacuum
rescaling/vacuum
E=10GeV
E=50GeV z z
can be approached by

23. Ratio of energy loss between heavy and light quark in QGP
Solid Curve:
Dashed curve: c b E
In the intermediate jet energy region the ratio increase rapidly with increasing energy.
In the very high jet energy region the effective energy loss of heavy quark is larger than one of light quark

24. IV. Summary
The modified fragmentation function in strong interacting medium (cold nucleus and QGP) has been calculated in pQCD.
The modified fragmentation function in QGP medium can be approached by rescaling fragmentation function with effective energy loss fraction For light quark , for heavy quark
3)The different effective energy fraction shift of the fragmentation function for light and heavy quark will help us to understand the different behavior of the light and heavy quark jet.

25. Thank You