1. Intrinsic transverse momentum and the Sivers effect #
Aram Kotzinian
Torino University & INFN
On leave in absence from YerPhI, Armenia and JINR, Russia
Intrinsic transverse momentum of quarks
Why it is actual
Cahn effect
Single target spin asymmetries
Sivers effect
Collins effect
In collaboration with
M. Anselmino, M. Boglione, U. D'Alesio, F. Murgia & A. Prokudin
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

2. Transversity workshop
SIDIS
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

3. Intrinsic transverse momentum role
Gluon polarization measurement LP
QCDCompton
PGF
R strongly depends on the intrinsic and fragmentation
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

4. Unpolarized SIDIS & Cahn effect
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

5. Transversity workshop
approximation
Ji et al: QCD factorization holds for
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

6. Transversity workshop
Comparison with data
EMC, 280 GeV muon SIDIS
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

7. Hadron transverse momentum dependence
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

8. Transversity workshop
Collins Effect
azimuthal modulation of transversely polarized quark FF
Side view
Front view
Up-Down asymmetry = 0
Nonzero Left-Right asymmetry
Schaefer-Teryaev SR:
hadrons transverse momenta
are compensated in the
quark fragmentation
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

9. Transversity workshop
Sivers Effect
Azimuthal modulation of quark transverse momentum for a transversely polarized nucleon
Unpolarized DF:
Polarized DF:
Quark transverse momentum is compensated by that of target remnant
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

10. Transversity workshop
SSA
Analyzing power:
Only Sivers effect
Only Collins effect
Analysis by Anselmino et al, E704
STAR
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

11. Transversity workshop
HERMES SSA
One can describe the data using only Collins effect
Schweitzer & Bacchetta: there is a room for Sivers effect
Efremov, Goeke & Schweitzer: one can neglect the Sivers effect
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

12. Parameterization for Sivers effect
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

13. Transversity workshop
Anselmino et al
for E704 SSA
u-quark
d-quark
Our parameterization:
opposite sign & high
values at small x
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

14. Results: p on P & D targets
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

15. Transversity workshop
Results: K on D target
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

16. Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

17. Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

18. Quark intrinsic transverse momentum in LEPTO
- Generate virtual photon – quark scattering in collinear configuration:
- Before
- After
- Generate intrinsic transverse momentum of quark (Gaussian)
- Rotate
- Generate uniform azimuthal distribution of quark
- Rotate
- Generate quark azimuthal angle according to Sivers distribution
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

19. Modified LEPTO MC predictions for JLAB SSA
Opposite signs of asymmetry in the target and current fragmentation
In principle, one can check origin of by measuring it in the TFR
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

20. Transversity workshop
Electron Ion Collider
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

21. Modified LEPTO MC predictions for EIC SSA
Opposite signs of asymmetry in the target and current fragmentation
In principle, one can check origin of by measuring it in the TFR
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

22. Transversity workshop
End of Story?
Zoology of FracFun
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian

23. Transversity workshop
Conclusions
Intrinsic transverse momentum in simple parton model approach allows to describe
Hadron transverse momentum dependence in SIDIS
Cahn effect
HERMES SSA data on longitudinally polarized target
It is important to investigate the SSA in the TFR
Sivers effect?
Collins effect from target remnant hadronization?
We need more precise data on transversely polarized targets
Transversity workshop
Trento, June 16, 2004
Aram Kotzinian