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Tomohiro Kobayashi Tokyo Institute of Technology

Single-spin asymmetry in interference fragmentation on a transversely polarized hydrogen target at HERMES. Tomohiro Kobayashi Tokyo Institute of Technology. Contents Transversity & Semi-inclusive DIS with transversely polarized target SSA in HERMES (data taking period : 2002~2004)

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Tomohiro Kobayashi Tokyo Institute of Technology

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  1. Single-spin asymmetry in interference fragmentation on a transversely polarized hydrogen target at HERMES Tomohiro Kobayashi Tokyo Institute of Technology • Contents • Transversity & • Semi-inclusive DIS with transversely polarized target • SSA in HERMES (data taking period : 2002~2004) • Conclusion Semi-Inclusive Reactions (SIR) Workshop 2005 (May 19th)

  2. Motivation Understand spin structure of the nucleon Quark transversity is one of the important aspects of relativistic nature of quarks inside the nucleon.

  3. Access to transversity 1 hadron semi-inclusive DIS : Collins FF (chiral odd) 2 hadron semi-inclusive DIS

  4. ：Interference FF (chiral odd) Access to transversity 2 hadron semi-inclusive DIS A. Bacchetta and M. Radici, Proceedings of DIS’2004 (2004), hep-ph/0407345 f + f q sin( ) sin A ~ h H ^ R S 1 1 UT h H are not convoluted with . 1 1

  5. Longitudinally polarized deuterium target v.r.t. virtual photon direction w.r.t. beam direction First measurement of Small asymmetry is observed

  6. , s-p wave interference in ππ scattering theory Partial wave expansion R. L. Jaffe, Xuemin Jin, and Jian Tan, Phys. Rev. Lett. 80, 1166 (1998) P. Estabrooks and A. D. Martin, Nucl. Phys. B79, 301 (1974) The sign changes at

  7. Spectator model for fragmentation Radici et al., hep/ph-0110252 No strong dependence.

  8. SSA in

  9. Event selection Data set : 2002~2004 SIDIS events with at least pion pair( ) appeared were analyzed. Kinematic cuts : ≥ 1 GeV2 ≥4 GeV2 ≥0.023 0.1 < < 0.85 > 2.5 GeV (for DIS lepton) > 1 GeV (for Hadron) > 2 GeV, where To cut exclusive channel.

  10. Evaluate What is measured where is the average target polarization. ( )

  11. Fit with 0.51 < < 0.97 GeV

  12. Fit with Sign of the asymmetry does not change around binning : 0.25, 0.40, 0.55, 0.77, 2.0 [GeV]

  13. f + f q µ sin( ) sin A h H ^ R S 1 1 UT Conclusion • Transversity and interference fragmentation function are related to SSA : • HERMES has been taking data with transversely polarized hydrogen target since 2002. • SIDIS events with at least two hadrons ( ) were analyzed. • Asymmetry of order 4% is observed. • Around , asymmetry becomes large. • No sign change is observed.

  14. Outlook • 3.5 M DIS evens • in 2002~2004. • 3~3.5 M events is • expected in 2005.

  15. backup

  16. spectrum With or without cut

  17. spectrum With or without cut

  18. double spin asymmetry Fit for both beam polarization. No double spin asymmetry Beam polarization (%) Beam polarization don’t affect to the asymmetry

  19. Angle distribution Correlation in the distribution due to the HERMES acceptance and spectrometer magnet field. Monte Carlo studies show : no face asymmetries Due to those correlations

  20. Single spin asymmetry Hadron scattering plane Lepton scattering plane Target spin vector ⇒ fit with

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