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Transversity Physics Update

This update discusses the observations of large azimuthal asymmetries in single-spin asymmetry (SSA) at HERMES, various origins for the observed SSA, the need for transversely polarized target data, and measurements of Sivers and Collins asymmetries. It also explores the implications for the JLab experiment and the importance of understanding spin structure in the nucleon.

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Transversity Physics Update

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  1. Transversity Physics Update Jen-Chieh Peng University of Illinois at Urbana-Champaign Polarized 3He and Tansversity Collaboration Meeting, JLab, October 21-22, 2005

  2. What were known when PR03-004 was proposed? • 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 HERMES • Data can be described by models considering only Transversity or Sivers distribution alone. • Need transversely polarized target SSA data

  3. AUTsin() from transv. pol. H target “Collins“ moments Simultaneous fit to sin( + s) and sin( - s) hep-ex/0408013 hep-ex/0507013

  4. Sivers moments from transversity experiments AUTsin() from Hermes transv. pol. H target “Sivers“ moments hep-ex/0408013 hep-ex/0507013 First measurement of Siversasymmetry Sivers function nonzero  orbital angular momentum ofquarks

  5. Collins asymmetryfromCOMPASS Transversely polarized 6LiD target Cover smaller x Consistent with 0 hep-ex/0503002 COMPASS 2002-2004 data: ~ factor of 4 in statistics

  6. Extraction of Sivers functions from the Sivers moment measurements Fits to the Hermes data “Prediction” of the Compass data Anselmino et al. hep/ph/0501196

  7. Extraction of Sivers functions from the Sivers moment measurements Fits to the Hermes data “Prediction” of the Compass data Anselmino et al. hep/ph/0507181

  8. Extraction of Sivers functions from the Sivers moment measurements Fits to the Hermes data “Prediction” of the Compass data Vogelsang and Yuan hep/ph/0507266

  9. Extraction of Collins functions from the Collins moment measurements Fits to the Hermes data “Prediction” of the Compass data Vogelsang and Yuan, hep/ph/0507266

  10. Is the Hermes AUL data consistent with AUT data? A combined analysis of the AUL and the AUT data Sub-leading twist Data Contributions from Collins and Sivers HERMES hep-ex/0505042

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

  12. Prediction of SSA for π○ production Vogelsang and Yuan, hep/ph/0507266

  13. Prediction for Sivers Moments at 6 GeV Anselmino et al. hep/ph/0507181

  14. 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?

  15. 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.

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