Transversity Physics Update

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

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AUTsin(?) from transv. pol. H target
Collins moments
Simultaneous fit to sin(? ?s) and sin(? - ?s)
hep-ex/0408013
hep-ex/0507013
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Sivers moments from transversity experiments
AUTsin(?) from Hermes transv. pol. H target
Sivers moments
hep-ex/0408013
hep-ex/0507013
First measurement of Sivers asymmetry
Sivers function nonzero ?? orbital angular
momentum of quarks
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Collins asymmetry from COMPASS

• Transversely polarized 6LiD target
• Cover smaller x
• Consistent with 0

hep-ex/0503002
COMPASS 2002-2004 data factor of 4 in
statistics
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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
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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
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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
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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
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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
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Comparison between the HERMES transversely
polarized target data with the Chiral-quark
soliton model
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Prediction of SSA for p? production
Vogelsang and Yuan, hep/ph/0507266
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Prediction for Sivers Moments at 6 GeV
Anselmino et al. hep/ph/0507181
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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 gt New additional
  goals Independent checks for the striking flavor
  structures of the Sivers and Collins functions.
• Compare the merits of p versus p- detections.
• Feasibility for measuring SSA with p0 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.