1. Quark-quark double scattering in nuclei with twist expansion approach
Ben-Wei Zhang
1. Texas A&M University, USA
2. Central China Normal University, China
Based on the work in collaboration with X.-N. Wang and A. Schaefer

2. Outline
Introduction
Modified FF due to quark-quark scattering with twist expansion approach
Multiplicity ratios of hadrons in nuclei
Summary

3. Jet quenching has been observed as a new nuclear phenomenon at RHIC
hadrons ph
parton E
Jet quenching has been observed as a new nuclear phenomenon at RHIC
X.N. Wang, Nucl.Phys. A750 (2005) 98

4. Quark-Quark Double Scattering
Two kinds of double scattering in eA DIS
quark-gluon
double scattering
quark-quark
double scattering
X.F. Guo, X.N. Wang, PRL85,3591(2000)

5. Properties of q-q double scattering
Quark-quark double scattering will mix the quark and gluon fragmentation functions;
Jet conversion;
Quark-quark double scattering may give different modifications to quark FF and anti-quark FF.
X.N. Wang and X.F. Guo, NPA 696, 788 (2001)
W. Liu, C.M. Ko, B.W. Zhang, nucl-th/
B.W. Zhang, X.N. Wang, A. Schaefer, in preparation

6. Generalized Factorization
Consider a typical quark-quark
double scattering process in
semi-inclusive eA DIS:
J. Qiu,G. Sterman, NPB 353(1991)105; NPB 353(1991)137

7. Interference effect
interference effect

8. Other processes ……
lowest order
without radiation

9. Quark-quark double scattering
Single Scattering: leading twist contribution
Double Scattering: twist-4 contribution

10. Modified Fragmenation Function
Summing single and double scattering gives
We define the modified quark FF as:

11. Quark-quark correlation function
M. Luo, J. Qiu,G. Sterman, PRD 50(1994)1951.
J. Osborne and X.N. Wang, NPA 710(2002)281.

12. Quark and anti-quark FF(I)
We get the modification to quark FF as:
Similarly we can obtain
modification to
anti-quark FF.

13. Quark and anti-quark FF(II)
The difference between modified quark FF and modified anti-quark FF:

14. Multiplicity ratios of hadrons
Multiplicity ratio measured at HERMES:
HERMES
hep-ex/
hep-ex/

15. Theoretical explanation
In the constituent quark model:

16. Summary
Quark-quark scattering is eA DIS are studied with twist expansion approach
Modification to quark FF in nuclei is different from the modification to anti-quark FF in nuclei.
This difference may explain the multiplicity ratios of hadrons in nuclei observed at HERMES.

17. Summary (cont.)
Quark-quark double scattering can modify fragmentation functions without radiation.
Quark-quark double scattering may change the flavor of partons: jet conversion
In heavy-ion collisions quark-quark double scattering can not be neglected if quark density is comparable to gluon density in hot nuclear medium.

18. Thank you!
谢谢！

19. BACKUP

20. quark-quark correlation function

21. Hard partonic part
Semi-inclusive hadronic tensor can be given: