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:
November 2005
Tokyo Tech

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)
November 2005
Tokyo Tech

4. Interference FF
Expansion of in Legendre moments: Jaffe et al. [hep-ph/ ]:
describe interference between 2 pion pairs
coming from different production channels
November 2005
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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 (times -1 -> trento conventions) based on the spectator model
November 2005
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6. The polarized cross sections
The AUL & AUT asymmetries are related to these polarized cross
sections (subleading twist, Bacchetta et al.):
November 2005
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7. before integration over
Bacchetta et al. [hep-ph/ ]
November 2005
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8. transversely polarized hydrogen target
Single Spin Asymmetry
transversely polarized hydrogen target
What is measured:
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9. longitudinally polarized deuterium
Hint of a sign change
at the r0 mass!
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10. long. pol. deuterium, x-dependence
higher x: hint of sign change at
r0 mass according to Jaffe’s model ?
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11. long. pol. deuterium, z-dependence2
sign change at r0 according to
Jaffe’s model for low z
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12. The AUT asymmetry
Significant
behavior!
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13. Invariant mass dependence
see f.i. M. Radici, hep-ph/
positive asymmetry moments
for all invariant mass bins
result rules out predicted
sign change at the r0 mass
(Jaffe et al.)
Preliminary
November 2005
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14. 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
November 2005
Tokyo Tech

15. 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
November 2005
Tokyo Tech