Toshi-Aki Shibata Tokyo Tech

1. Jan 12, 2007 KEK 陽子のスピン構造 　－これまでにわかったことと今後の展望 Spin Structure of The Proton 　－What has been learned and what to be learned more Toshi-Aki Shibata Tokyo Tech Contents: • Deep Inelastic Scattering: lepton scattering and pp collision • Unpolarized and Polarized Gluon Distribution • Quark Helicity Distribution – Flavor Separation • Physics with Transverse Targets

2. http://www.nucl.phys.titech.ac.jp/~qcd-jsps/

4. Semi-inclusive Measurements in Deep Inelastic Scattering • Inclusive measurement, e’ e’ x is determined event by event • Semi-inclusive measurement, • e’ and e ‘Flavor tagging’ ( quark distribution ) x ( fragmentation function ) Scaling x, z, Q2 z is determined for each hadron

5. pp collisions gg, gq… collisions measured as a function of pt xbj, z integrated two xbj’s involved in each event

6. Gluon Distributions - Unpolarized and Polarized DURHAM HEP Databases, online plot http://durpdg.dur.ac.uk/hepdata/pdf3.html

7. DURHAM HEP Databases, online plot http://durpdg.dur.ac.uk/hepdata/pdf3.html S. Kretzer, H.L. Lai, F.I. Olness, W-K. Tung Phys.Rev. D69 (2004) 114005 CTEQ6

9. First moment at

10. Second Moment Linear momentum

11. Lepton scattering hadron pair production charm-anticharm production pp collisions π0 production prompt photon production (gq → qγ) …

12. Projection

13. Helicity Distributions of Partons in the Nucleon Contents: • ・ A1 and g1 Measurement • Semi-inclusive Measurement of Hadrons with a precise PID • Flavor Separation of Quark Helicity Distributions

14. Quark Helicity Distributions, Flavor Separation Double-spin asymmetry Beam and target, both polarized Virtual photon Nucleon

15. (EMC’s Flavor Decomposition with First Moments) Proton Spin EMC Experiment (1988) SMC, SLAC 20 – 30 % of Nucleon Spin ‘Nucleon Spin Problem’

16. Main Features of HERMES：　 HERa MEasurement of Spin 1995 – at DESY • Polarized Electron (Positron) Beam of HERA • E = 27.6 GeV, P 60% • Internal Gas Targets • Longitudinally polarized 3He, D, HP（H） 85% • Transversely polarized H --- now running • Unpolarized High Density Targets (H2, D2, He, N2, Ne, Ar, • Kr, Xe) • Semi-inclusive Measurement, Hadron Detection with a good • PID of , K, p • Ring Imaging Cherenkov Counter　（RICH)

17. Precision Measurements of g1(x) : Inclusive Measurement Proton Deuteron Q2depencence is weak

18. xg1(x) Good agreement among different measurements

19. Flavor Separation of Quark Helicity Distributions at HERMES HERMES, A. Airapetian et al., Phys. Rev. D71 (2005) 012003 HERMES, A. Airapetian et al., Phys. Rev. Lett. 92 (2004) 012005

20. 1 / 2 1 / 2 + + = 1 / 2 - 1 / 2 Proton Spin from Viewpoint of Quark Flavors SU(6) Quark Wave Functions of Baryons Sum of Spins of u u d Quarks = Spin of Proton

21. Semi-Inclusive Measurement SMC: h+, h- is assumed QCD fits to Inclusive Data assume Sea Quark Flavor Symmetry in most cases 16 parameters for example First moments of u and d fixed from neutron lifetime and hyperon weak decay in the framework of SU(3)

22. Semi-inclusive Measurements in Deep Inelastic Scattering x Bin by Bin Separation • Inclusive measurement, e’ e’ x is determined event by event • Semi-inclusive measurement, • e’ and e ‘Flavor tagging’ ( quark distribution ) x ( fragmentation function ) Factorization x, z, Q2 z is determined for each hadron

23. Quark Helicity Distributions , Flavor Separation Semi-inclusive DIS Cross Section Double-Spin Asymmetry Quark Density Distributions Quark Helicity Distributions unpol. PDF and FF from data of unpol. semi-inclusive DIS unconstrained

24. A1(x), A1h(x) Deuteron h+ K+ h- K-

25. Quark Helicity Distributions, Flavor Separation Double-Spin Asymmetries Ah1 (d) from Semi-inclusive DIS Hadron identification for the first time Ah1(x) K+ K- x x asymmetries similar to inclusive asymmetry, except asymmetry.

26. P(x) 4x6 Matrix in each x bin

27. Error band – systematic error QCD fits to inclusive measurements

28. Flavor Separation of Quark Helicity Distributions Result: • x bin by bin analysis except • for smearing correction • First moment from neutron • lifetime and hyperon decay • not used x • No functional forms as a • function of x are assumed • Helicity conservation not • assumed ( )

29. x Integral in Measured Region xmin= 0.023, xmax = 0.6

30. Conclusions of this part • HERMES is a Deep Inelastic Scattering Experiment • at HERA-DESY with 27.6 GeV Electron (Positron) Beam • and Polarized Internal Gas Targets • ,K, p Identification with RICH • A1(x), g1(x), and A1h(x) are measured • Flavor Separation of Quark Helicity Distribution • from Semi-Inclusive Measurement with , K Identification • for the First Time, an Independent Extraction from data of DIS • Positive u, negative d Distributions, Sea Quarks nearly zero

31. Single Spin Asymmetry with a Transversely Polarized Hydrogen Target at HERMES - Separation of Collins Effect and Sivers Effect

32. 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 2004 data

33. Quark Distribution Functions At leading twist Quark Momentum Distribution Quark Helicity Distribution Quark Transversity Distribution Positivity Bound Soffer Bound

34. 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.

35. Two Azimuthal Angles in Semi-inclusive Measurement with a Transversely Polarized Target electron reaction plane hadron Target

36. 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

37. 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

38. Collins Asymmetry Phys. Rev. Lett. 94 (2005) 012002 Positive Asymmetry Negative Asymmetry The magnitude is larger.

39. Sivers Asymmetry Phys. Rev. Lett. 94 (2005) 012002 Positive Asymmetry Asymmetry is nearly 0 Effects of Exclusive Vector Meson Production were studied.

40. Update including Data 2004 Collins Sivers

41. Conclusions of this part • 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.

42. Summary Gluon distribution, Uｎpolarized and polarized Several approaches with lepton scattering and pp collisions Quark helicity distributions, quark flavor separation Quark physics with transversely polarized proton Collins effect Sivers effect - Orbital angular momentum Generarized Parton Distributions -- Jq Fragmentation processes – Fragmentation functions Spin Structure of The Proton is a Fundamental Subject of QCD.