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

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2 What were known when PR03-004 was proposed? HERMES Large Azimuthal asymmetries were observed in SSA at HERMES for H 2 and D 2 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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3 A UT sin( ) 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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4 Sivers moments from transversity experiments Sivers moments A UT sin( ) from Hermes transv. pol. H target First measurement of Sivers asymmetry Sivers function nonzero orbital angular momentum of quarks hep-ex/0408013 hep-ex/0507013

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

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

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

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

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

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

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

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

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

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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 π 0 detection at JLab?

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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 3 He 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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