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

Outline

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

Jet Quenching

parton

E

hadrons

p h

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

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) 4

Properties of q-q double scattering

 X.N. Wang and X.F. Guo, NPA 696, 788 (2001) Quark-quark double scattering will mix the quark and gluon fragmentation functions; Jet conversion;  W. Liu, C.M. Ko, B.W. Zhang, nucl-th/0607047 Quark-quark double scattering may give different modifications to quark FF and anti-quark FF.

B.W. Zhang, X.N. Wang, A. Schaefer, in preparation 5

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 6

Interference effect

interference effect 7

Other processes

…… …… lowest order without radiation 8

Quark-quark double scattering

 Single Scattering: leading twist contribution   Double Scattering: twist-4 contribution 9

Modified Fragmenation Function

 Summing single and double scattering gives  We define the modified quark FF as: 10

Quark-quark correlation function

M. Luo, J. Qiu,G. Sterman, PRD 50(1994)1951.

J. Osborne and X.N. Wang, NPA 710(2002)281.

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Quark and anti-quark FF(I)

 We get the modification to quark FF as:  Similarly we can obtain modification to anti-quark FF.

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Quark and anti-quark FF(II)

 The difference between modified quark FF and modified anti-quark FF: 13

Multiplicity ratios of hadrons

 Multiplicity ratio measured at HERMES: HERMES hep-ex/0012049 hep-ex/0307023 14

Theoretical explanation

 In the constituent quark model: 15

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.

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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.

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Thank you!

谢谢！ 18

BACKUP

quark-quark correlation function

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Hard partonic part

 Semi-inclusive hadronic tensor can be given: 21