1. Single Spin Asymmetry with a Transversely Polarized
Hydrogen Target at HERMES
Toshi-Aki Shibata
　　　　　　　Tokyo Tech
　　　for HERMES Collaboration
Contents:
Physics with DIS on Transversely Polarized Targets
HERMES Experiment
Separation of Collins Effect and Sivers Effect
HAWAII05 T.-A. Shibata

2. Airapetian et al, HERMES, Phys. Rev. Lett. 94 (2005) 012002
Single-Spin Asymmetries in Semi-inclusive Deep-Inelastic
Scattering on a Transversely-Polarized Hydrogen Target
+ update including the data
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3. Quark Distribution Functions
At leading twist
Quark Momentum Distribution
Quark Helicity Distribution
Quark Transversity Distribution
Positivity Bound
Soffer Bound
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4. Why Are Quark Transversity Distributions Interesting?
proves Quark’s Relativistic Nature in the
Nucleon
Because of Lack of Transversity of Gluon, Q2 Evolution
Should Be Different From That of and
Chiral Odd. So Far Never Measured
initial quark transverse momentum
final quark transverse momentum
Sivers Effect:
could be related to orbital motion of quarks
The separation of the two effects was carried out for the first time.
HAWAII05 T.-A. Shibata

5. e＋ HERMES Detector 27.5 GeV Reconstruction Kinematical Range
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6. in Semi-inclusive Measurement with a Transversely Polarized Target
Two Azimuthal Angles
in Semi-inclusive Measurement with a Transversely
Polarized Target
electron
reaction plane
hadron
Target
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7. Azimuthal Single Spin Asymmetry
Asymmetry around the virtual photon direction
Collins
Sivers
means convolution Integral over initial (pT )
and final (kT ) quark transverse momentum
Fourier Component
Fit in 2-dimension in each x bin
Collins
Sivers
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8. Monte Carlo Test of Extraction Method
generate Collins and Sivers Asymmetries (Gaussian Ansatz in Pt2)
analyse MC data like experimental data and extract Asymmetries
Collins-Sivers cross contamination is negligible
HAWAII05 T.-A. Shibata

9. The magnitude is larger.
Collins Asymmetry
Phys. Rev. Lett. 94 (2005)
Positive Asymmetry
Negative Asymmetry
The magnitude is larger.
HAWAII05 T.-A. Shibata

10. Sivers Asymmetry Positive Asymmetry Asymmetry is nearly 0
Phys. Rev. Lett. 94 (2005)
Positive Asymmetry
Asymmetry is nearly 0
Effects of Exclusive Vector
Meson Production were studied.
HAWAII05 T.-A. Shibata

11. Update including Data 2004
Collins
Sivers
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12. Conclusions
The separation of Collins effect and Sivers effect was carried
out for the first time.
Non-zero asymmetry is observed for Collins asymmetry.
Positive asymmetry, negative asymmetry are compatible
with helicity distribution 　　　 . But the amplitude of
asymmetry is large.
asymmetry is positive, and asymmetry is nearly 0
for Sivers asymmetry. The effects of exclusive vector
meson production were investigated and found to be
negligible.
outlook:
Statistics will be about doubled by the end of 2005.
HAWAII05 T.-A. Shibata