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Transversity Physics Update

Jen-Chieh Peng

Polarized 3He and Tansversity Collaboration Meeting, JLab, October 21-22, 2005

University of Illinois at Urbana-Champaign

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What were known when PR03-004 was proposed? HERMES

• Large Azimuthal asymmetries were observed in SSA at HERMES for H2 and D2 targets

• Several possible origins for the observed SSA

- Transversity + Collins

- Sivers

- Sub-leading twist effect

• Data can be described by models considering only Transversity or Sivers distribution alone.

• Need transversely polarized target SSA data

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COMPA

J

SS ( , )

HERMES ( , )

Lab ( , )

d

p e e x

e e

He e e x

x

3

1

, , 1 1

1

Product of ( ) ( ) is non-zero

Assume ( ) from model, then / 1

Extraction of ( ) requires an independent measurement of

Collins function ( )

unfavored favored

q x H z

q x H H

q x

H z

AUTsin() from transv. pol. H target

Simultaneous fit to sin( + s) and sin( - s) “Collins“

moments

hep-ex/0408013

hep-ex/0507013

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Sivers moments from transversity experiments

“Sivers“ moments

AUTsin() from Hermes transv. pol. H target

First measurement of Sivers asymmetry

Sivers function nonzero orbital angular momentum of quarks

hep-ex/0408013hep-ex/0507013

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Collins asymmetry from COMPASS

COMPASS 2002-2004 data: ~ factor of 4 in statistics

hep-ex/0503002

• Transversely polarized 6LiD target

• Cover smaller x

• Consistent with 0

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Extraction of Sivers functions from the Sivers moment measurements

Fits to the Hermes data “Prediction” of the Compass data

0.42 0.18, 1.0 1. 1.0 1.98, , 1.0 1.9V V uu d d

N NN N

Anselmino et al. hep/ph/0501196

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Extraction of Sivers functions from the Sivers moment measurements

Fits to the Hermes data “Prediction” of the Compass data

0.33 0.13, 1.0 0.11V Vu dN N

Anselmino et al. hep/ph/0507181

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Extraction of Sivers functions from the Sivers moment measurements

Fits to the Hermes data “Prediction” of the Compass data

0.81 0.07, 1.86 0.28u dS S

Vogelsang and Yuan hep/ph/0507266

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Extraction of Collins functions from the Collins moment measurements

Fits to the Hermes data “Prediction” of the Compass data

0.29 0.04, 0.33 0.04fav unfavC C

Vogelsang and Yuan, hep/ph/0507266

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Is the Hermes AUL data consistent with AUT data?A combined analysis of the AUL and the AUT data

Contributions from Collins and Sivers

Data

Sub-leading twist

HERMES

hep-ex/0505042

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Comparison between the HERMES transversely polarized target data with the Chiral-quark soliton model

disf fav1 1( ) 1.2 ( )H z H z

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Prediction of SSA for π○ production

Vogelsang and Yuan, hep/ph/0507266

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Prediction for Sivers Moments at 6 GeV

Anselmino et al. hep/ph/0507181

( , )p e e x

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Implications for the JLab experiment

• Simulation of the experimental sensitivities using the most recent parametrizations of Collins and Sivers functions.

• Previous main goal: flavor dependence of the transversity distributions => New additional goals: Independent checks for the striking flavor structures of the Sivers and Collins functions.

• Compare the merits of π+ versus π- detections.• Feasibility for measuring SSA with π0 detection at

JLab?

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Summary• Transversity distribution remains an interesting

frontier in understanding spin structure in nucleon.• Study of the T-odd Sivers structure function and the

Collins fragmentation function are important for their own sake, and for extracting information on transversity.

• First results of SSA using transversely polarized p and d targets are intriguing. The proposed Hall-A measurement on 3He should provide very useful new information.

• New Semi-Inclusive DIS experiments at JLab will continue to probe the flavor structure of unpolarized and polarized parton distributions.