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Advancements in QCD Spin Structure of Nucleons: Summary and Future Outlook

This session summary highlights key discussions on helicity distributions, gluon polarization, and transversity in nucleons. Notable talks included data sets for helicity distributions, quark distributions, and gluon polarization, as well as advancements in determining PDFs and FFs. The session also covered topics like evolution, prompt photons as probes for ΔG/G, and spin transfer processes in various interactions, with a focus on theoretical and experimental progress in understanding the spin structure of nucleons. Key presentations emphasized advancements in technology and methodologies for precise data collection and analysis, paving the way for future research in this field.

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Advancements in QCD Spin Structure of Nucleons: Summary and Future Outlook

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  1. Summay of Session 2 QCD spin structure of nucleons

  2. Summary Session 2 Introduction Helicity distributions Gluon polarisation transversity

  3. Summary of Session 2 • six excellent plenary talks: Metz, Barone, Garçon, Hasch, Bressan, Saito • 55 talks in parallel sessions, 16 h • half experiment / half theory • exp. talks: about 2/3 ℓp, 1/3 pp • theo. talks: about 1/3 on transversity and SSA Apologies for not being able to cover everything appropriately

  4. HELICITY DISTRIBUTIONS

  5. Final g1 for p, d, n Riedl • quasifinal data set for p and d • corrected for smearing (radcor, detector)

  6. Quark helicity distributions Rubin

  7. Inclusive asymmetries Peshekhonov inclusive • COMPASS deuteron data 2002 – 2003 • most precise data for x<3x10-2 • 2004 similar precision • kaon/pion asymmetries to come +vehadrons

  8. Δq - Theory • method using A and moments to determine • model-independent determination of from incl. and semi-incl. asym. in LO and NLO. Fragmentations functions cancel in needs very precise data (Jlab) Shevchenko Christova remark: A exp. diffcult with magnetic spectrometers

  9. Δq - JLAB Jiang • under construction (2006-2007) • expect very precise data for x > 0.1 • apply method Semi-SANE E04-113

  10. Evolution • role of higher twist in the determination of PDF. HT cancels largely in A1 . • small-x evolution:double logarithm resummation important forg1for x ≤ 10-3 -10-4 Stamenov Ermolaev • parametrisation-independent matrix solution of DGLAP • estimates of ΔG/G and Lqranges Goshtasbpour Ramsey

  11. GLUON POLARISATION

  12. ΔG/G - Photon-Gluon Fusion measured aLL: calculable partonic asymmetries R: Monte-Carlo (Lepto for Q2 > 1 GeV2)

  13. ΔG/G - SMC Rondio • event selection high-pT pairs • Q2 > 1 GeV2 • neural network • ΣpT2 > 2.5 GeV2 • RPGF = 0.32 Hermes (all Q2) SMC pT12+pT22 NN xg

  14. ΔG/G - COMPASS Schill • Analysis a la SMC • ΣpT2 > 2.5 GeV2, Q2 > 1 GeV2 • open charm signal 10% of statistics 2002/3 PGF: cc open charm Hermes Compass 2002/3 SMC

  15. ΔG/G – RHIC pp π0

  16. ΔG/G - Phenix: ALL for π0 Fukao 2003/4 Outlook 2005/7

  17. ΔG/G – Star: ALL jets (2005) 1.0 Inclusive Jets :LO W. Vogelsang 0.8 STAR qg 0.6 0.4 gg qq 0.2 0.0 0 5 10 15 20 25 30 Sowinski 2005 pT (GeV)

  18. NLO and NLL Vogelsang • Resummation of NLL important for single-inclusive processes ( , ) • Crucial for lower energy fixed target • Excellent agreement of NLO + NNL calculations with collider data! • prompt photons good probe for ΔG/G at RHIC

  19. Prompt photons/π0 π0 prompt γ Vogelsang, Okada

  20. RHIC detector upgrades GS95 prompt photon central arms NCC • important enlargement ofxgcoverage  first moment Tungsten-Silicon sampling calorimeter Kinney Togawa Silicon vertex barrel detector 2009 2007-2008

  21. Proposals • Spintransfer in Hyperon production in pp Xu, Rykov • Polarised DY p↑ p↑at GSI (transversity) Efremov

  22. TRANSVERSE SPIN

  23. AN for pp -> π0X STAR Makdisi Ogawa xF = 0

  24. SSA andintrinsic kT Murgia, D’Alesio • A generalized pQCD approach to SSA and unpol. cross sections: LO.pQCD + spin and new kT-dependent PDF and FF • AN (p↑pπX): • Sivers effect contributes, Collins effect suppressed • suppressed for xF<0 for all mechanisms • good agreement with STAR data AN (p↑pπ0X)

  25. Intrinsic kT (continued) Boglione In the same model it was shown that • AN(p↑pDX)is an ideal process to study the Sivers distribution functions of quarks and gluons • TheHermes data can be described as well as the unpolarised Cahn asymmetries from EMC using Prokudin

  26. p↑ p↑ cross section in NLO Mukherjee • first NLO calculation • example: prompt photon at Phenix • scale dependence significantly reduced • study of K-factors for DY Ratcliffe

  27. Hermes Collins & Sivers Schnell

  28. COMPASS Collins & Sivers Pagano Collins Sivers

  29. Dihadron fragmentation h1 quark h2 Bacchetta • New quark polarimeter • simpler, no kT convolution, cf van der Nat Joosten

  30. More Asymmetries Gamberg • Boer-Mulders function • AUL • Model for transversity and intrinsic motion of quarks • Chiral-odd twist-3 DF e(x) • New observables from color gauge invariance Kinney Zavada Wakamatsu Pijlman

  31. Spin transfer to Λ • Spin transfer to Λ Alexakhin • transverse Λ polarisation Friedrich Belostotski

  32. Exclusive ρ production • SDME: • Model Neyret Goloskokov

  33. GPDs • DVCS Beam Charge Asymmetry new: deuteron • Hard exclusive ππ • Exclusive πand vector mesons • Hermes recoil detector Marukyan Fabbri Rostomyan Stewart

  34. More from theory Leader • Spin sum rule revisited • problem in derivation of • rigorous treatment yields miraculously same SR • new sum rule for transverse spin • Higher twist resummation • Asymmetries in SIDIS Teryaev Di Salvo

  35. Fragmentation functions • Determination of polarised fragmentation from Belle data in progress • Possible difficulties with LUND fragmentation at low energies • Q2 dependence of GDH Seidl Kotzinian Nagaitsev

  36. Personal Impression • Two new facilities are working perfectly: RHICand COMPASS • Enormous progress on theory of transverse spin and SSA • Is ΔG/G small? Exciting times ahead

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