1. First results on two-hadron interference fragmentation on a transversely polarized hydrogen target Paul van der Nat (on behalf of the HERMES collaboration) Layout:Introduction Results on longitudinally polarized target Results on transversely polarized target Status of the analysis Conclusions & Outlook

2. November 2005 2 Tokyo Tech Introduction - 1  fragmentation Difficulties: extraction of difficult, needs weighting with Sivers & Collins entangled:

3. November 2005 3 Tokyo Tech Introduction - 2  fragmentation Integrate over : left with only Advantages: cross section asymmetry directly proportional to (no weigthing needed) (no weigthing needed) No Collins/Sivers “entanglement” Completely independent from 1  analysis Disadvantages: less statistics unknown (but can be measured at Belle & Babar) unknown (but can be measured at Belle & Babar)

4. November 2005 4 Tokyo Tech Interference FF Expansion of in Legendre moments: Jaffe et al. [hep-ph/9709322]: Jaffe et al. [hep-ph/9709322]: describe interference between 2 pion pairs coming from different production channels

5. November 2005 5 Tokyo Tech Interference FF Expansion of in Legendre moments: Radici et al. [hep-ph/0110252]: Radici et al. [hep-ph/0110252]: complety different model, not predicting complety different model, not predicting a sign change of the asymmetry around a sign change of the asymmetry around the (times -1 -> trento conventions) the (times -1 -> trento conventions) based on the spectator model based on the spectator model

6. November 2005 6 Tokyo Tech The polarized cross sections The A UL & A UT asymmetries are related to these polarized cross sections (subleading twist, Bacchetta et al.):

7. November 2005 7 Tokyo Tech before integration over Bacchetta et al. [hep-ph/0212300]

8. November 2005 8 Tokyo Tech Single Spin Asymmetry What is measured: transversely polarized hydrogen target

9. November 2005 9 Tokyo Tech longitudinally polarized deuterium Hint of a sign change at the  0 mass!

10. November 2005 10 Tokyo Tech long. pol. deuterium, x-dependence higher x: hint of sign change at  0 mass according to Jaffe’s model  0 mass according to Jaffe’s model ?

11. November 2005 11 Tokyo Tech long. pol. deuterium, z-dependence sign change at  0 according to Jaffe’s model for low z Jaffe’s model for low z 2

12. November 2005 12 Tokyo Tech The A UT asymmetry Significant behavior! behavior!

13. November 2005 13 Tokyo Tech Invariant mass dependence positive asymmetry moments for all invariant mass bins for all invariant mass bins result rules out predicted sign change at the  0 mass sign change at the  0 mass (Jaffe et al.) (Jaffe et al.) Preliminary see f.i. M. Radici, hep-ph/0510165

14. November 2005 14 Tokyo Tech Status of the analysis Dealing with low statistics: forced to integrate the asymmetry over many variables combined with the HERMES acceptance: watch out for combined with the HERMES acceptance: watch out for acceptance effects! acceptance effects! comparing different fitting methods for the extraction of the comparing different fitting methods for the extraction of the azimuthal moments: azimuthal moments: normal binned  2 fit versus unbinned max. likelihood fit normal binned  2 fit versus unbinned max. likelihood fit being studied using pythia MC data

15. November 2005 15 Tokyo Tech Conclusions & Outlook Conclusions: A (significantly) non-zero asymmetry-moment has been measured providing evidence for a non-zero interference fragmentation function. This also implies that interference fragmentation can be used to study transversity! The new results using a transversely polarized hydrogen target rule out the invariant mass behavior as predicted by R. Jaffe.Outlook: Increase the statistics using the 2005 data Extract asymmetry moment relating to Extract quantitative information on