Quark-quark double scattering in Quark-quark double scattering in nuclei nuclei

with twist expansion approachwith twist expansion approach

Ben-Wei ZhangBen-Wei Zhang

1. 1. Texas A&M University, USATexas A&M University, USA2. 2. Central China Normal University, ChinaCentral China Normal University, China

Based on the work in collaboration with X.-N. Wang and A. Schaefer

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OutlineOutline

IntroductionIntroductionModified FF due to quark-quark scattering Modified FF due to quark-quark scattering

with twist expansion approachwith twist expansion approachMultiplicity ratios of hadrons in nucleiMultiplicity ratios of hadrons in nucleiSummarySummary

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Jet QuenchingJet Quenching

Jet quenching has been observed as a Jet quenching has been observed as a new nuclear phenomenon at RHICnew nuclear phenomenon at RHIC

hadrons

ph

parton

E

X.N. Wang, Nucl.Phys. A750 (2005) 98

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Quark-Quark Double ScatteringQuark-Quark Double Scattering

Two kinds of double scattering in eA DISTwo kinds of double scattering in eA DIS

quark-gluon

double scattering

quark-quark

double scattering

X.F. Guo, X.N. Wang, PRL85,3591(2000)

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Properties of q-q double scatteringProperties of q-q double scattering

Quark-quark double scattering will mix the quark and Quark-quark double scattering will mix the quark and

gluon fragmentation functions;gluon fragmentation functions;

Jet conversion;Jet conversion;

Quark-quark double scattering may give different Quark-quark double scattering may give different modifications to quark FF and anti-quark FF.modifications to quark FF and anti-quark FF.

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

W. Liu, C.M. Ko, B.W. Zhang, nucl-th/0607047

X.N. Wang and X.F. Guo, NPA 696, 788 (2001)

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Generalized FactorizationGeneralized Factorization

Consider a typical quark-quarkConsider a typical quark-quark

double scattering process in double scattering process in

semi-inclusive eA DIS:semi-inclusive eA DIS:

J. Qiu,G. Sterman, NPB 353(1991)105; NPB 353(1991)137

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Interference effectInterference effect

interference effect

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Other processesOther processes

……

……

lowest order lowest order

without radiationwithout radiation

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Quark-quark double scatteringQuark-quark double scattering Single Scattering: leading twist contributionSingle Scattering: leading twist contribution

Double Scattering: twist-4 contributionDouble Scattering: twist-4 contribution

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Modified Fragmenation FunctionModified Fragmenation Function

Summing single and double scattering givesSumming single and double scattering gives

We define the modified quark FF as:We define the modified quark FF as:

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Quark-quark correlation functionQuark-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)Quark and anti-quark FF(I)

We get the modification to quark FF as:We get the modification to quark FF as:

Similarly we can obtainSimilarly we can obtain

modification to modification to

anti-quark FF.anti-quark FF.

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Quark and anti-quark FF(II)Quark and anti-quark FF(II)

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

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Multiplicity ratios of hadronsMultiplicity ratios of hadrons

Multiplicity ratio measured at HERMES:Multiplicity ratio measured at HERMES: HERMES

hep-ex/0012049

hep-ex/0307023

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Theoretical explanationTheoretical explanation

In the constituent quark model:In the constituent quark model:

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Summary Summary

Quark-quark scattering is eA DIS are studied Quark-quark scattering is eA DIS are studied with twist expansion approachwith twist expansion approach

Modification to quark FF in nuclei is different Modification to quark FF in nuclei is different from the modification to anti-quark FF in nuclei.from the modification to anti-quark FF in nuclei.

This difference may explain the multiplicity ratios This difference may explain the multiplicity ratios of hadrons in nuclei observed at HERMES.of hadrons in nuclei observed at HERMES.

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Summary (cont.)Summary (cont.)

Quark-quark double scattering can modify Quark-quark double scattering can modify fragmentation functions without radiation.fragmentation functions without radiation.

Quark-quark double scattering may change Quark-quark double scattering may change the flavor of partons: the flavor of partons: jet conversionjet conversion

In heavy-ion collisions quark-quark double In heavy-ion collisions quark-quark double scattering can not be neglected if quark scattering can not be neglected if quark density is comparable to gluon density in density is comparable to gluon density in hot nuclear medium.hot nuclear medium.

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Thank you! 谢谢！Thank you! 谢谢！

BACKUPBACKUP

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quark-quark correlation functionquark-quark correlation function

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Hard partonic partHard partonic part

Semi-inclusive hadronic tensor can be given:Semi-inclusive hadronic tensor can be given: