1. Paul van der Nat (on behalf of the HERMES collaboration)
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. Introduction - 1p fragmentation
Difficulties:
extraction of difficult, needs weighting with
Sivers & Collins entangled:
September 2005
Transversity 2005

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

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

5. Interference FF
Expansion of in Legendre moments: Radici et al. [hep-ph/ ]: complety different model, not predicting a sign change of the asymmetry around the
September 2005
Transversity 2005

6. The polarized cross sections
The AUL & AUT asymmetries are related to these polarized cross
sections (subleading twist, Bacchetta et al.):
September 2005
Transversity 2005

7. before integration over
Bacchetta et al. [hep-ph/ ]
September 2005
Transversity 2005

8. transversely polarized hydrogen target
Single Spin Asymmetry
transversely polarized hydrogen target
What is measured:
September 2005
Transversity 2005

9. longitudinally polarized deuterium
Hint of a sign change
at the r0 mass!
September 2005
Transversity 2005

10. long. pol. deuterium, x-dependence
higher x: hint of sign change at
r0 mass according to Jaffe’s model ?
September 2005
Transversity 2005

11. long. pol. deuterium, z-dependence2
sign change at r0 according to
Jaffe’s model for low z
September 2005
Transversity 2005

12. The AUT asymmetry Significant behavior! September 2005
Transversity 2005

13. Invariant mass dependence
positive asymmetry moments
for all invariant mass bins
result rules out predicted
sign change at the r0 mass
(Jaffe et al.)
September 2005
Transversity 2005

14. Status of the analysis Dealing with low statistics:
forced to integrate the asymmetry over many variables.
combined with the HERMES acceptance: watch out for
acceptance effects!
September 2005
Transversity 2005

15. Status of the analysis Dealing with low statistics:
forced to integrate the asymmetry over many variables
combined with the HERMES acceptance: watch out for
acceptance effects!
September 2005
Transversity 2005

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

17. 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
September 2005
Transversity 2005