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Spin physics with COMPASS

Spin physics with COMPASS. G. K. Mallot CERN/PH for the COMPASSCollaboration. Savin Fest, Dubna, 7.12.2010. The starting point. Smallness of ΔΣ confirmed by SMC! Where, oh where is the proton spin?. Elliot Leader. small EMC, SMC. unknown in 1997. unknown.

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Spin physics with COMPASS

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  1. Spin physics with COMPASS G. K. Mallot CERN/PH for the COMPASSCollaboration Savin Fest, Dubna, 7.12.2010

  2. The starting point Smallness of ΔΣ confirmed by SMC! Where, oh where is the proton spin? Elliot Leader small EMC, SMC unknownin 1997 unknown Savin Fest, Dubna, 7.12.2010

  3. Theory Input 1988 PLB 206 (1988) 309 ZPC 41 (1988) 239 PLB 212 (1988) 391 Savin Fest, Dubna, 7.12.2010

  4. Lepton-Photon 1989 G. Ross 1989 possible scenario: ∆G ≈ 6 (Q2=10 GeV2) ∆g/g(x) = 1 for xg > 0.1 still unresolved after SMC & SLAC Savin Fest, Dubna, 7.12.2010

  5. COMPASS Roots: in DIS (SMC, NMC, EMC) and spectroscopy (Wa89,WA102,xBarrel ) Goals: gluon polarization, flavour distributions, spin transfer meson spectroscopy, glue balls, polarisability Savin Fest, Dubna, 7.12.2010

  6. COMPASS Beam: 160 GeV µ+, pol. 80% from π decay Two-stage spectrometer 60 m long Hodoscopes SM2 E/HCAL1 Muon Wall 2 MWPC SM1 RICH1 E/HCAL2 Polarized Target MWPC, Gems, Scifi, W45 (not shown) 160 GeV µ beam Muon Wall 1, Rich Wall Straws, Gems Infrastructure Micromegas, SDC, Scifi Scifi, Silicon Savin Fest, Dubna, 7.12.2010

  7. June 1998 COMPASS fully approved in October 1998 Savin Fest, Dubna, 7.12.2010

  8. HCAL1: February 1999 - 2000 Savin Fest, Dubna, 7.12.2010

  9. 2001 HCAl1 and Muon Wall 1 Savin Fest, Dubna, 7.12.2010

  10. Straws Savin Fest, Dubna, 7.12.2010

  11. COMPASS 2004 Savin Fest, Dubna, 7.12.2010

  12. Parton Distribution Functions Three twist-2 PDFs unpolarised PDF quark with momentumxPin a nucleon well known – unpolarized DIS q(x) f1q (x) helicity PDF quark with spin parallel to the nucleon spinin a longitudinally polarised nucleon known – polarized DIS Dq(x) g1q(x) transversity PDF quark with spin parallel to the nucleon spin in a transversely polarised nucleon DTq(x) h1q(x) chiral odd, poorly known Savin Fest, Dubna, 7.12.2010

  13. Factorization & x-sect. asymmetries Semi-inclusive scattering long. double spin asymmetry transverse single asymmetry Inclusive scattering Savin Fest, Dubna, 7.12.2010

  14. COMPASS Target system solenoid 2.5T dipole magnet 0.5T acceptance ± 180 mrad 3He – 4He dilution refrigerator (T~50mK) 6LiD/NH3 50/90% pol. 40/16% dil. f. μ Savin Fest, Dubna, 7.12.2010

  15. Helicity structure Savin Fest, Dubna, 7.12.2010

  16. Proton asymmetries incl. π+ K+ π– K− • incl. & semi-incl. asymmetries, • similar data for deuteron Savin Fest, Dubna, 7.12.2010

  17. Q2 evolution of g1(x,Q2) p d CLAS HERMES • Q2dependence of g1 data related to gluon polarization (DGLAP) • Limited kinematic range (c.f. unpol. HERA) Savin Fest, Dubna, 7.12.2010

  18. The role of quark flavours LO semi-inclusive data analysis Savin Fest, Dubna, 7.12.2010

  19. Longitudinal spin transfer to  &  2003/2004 data 69500 Λ 41600 Λ Λ Λ • Large (!) DLL for Λrelated to antistrange quark distribution JINR, Dubna, June 21, 2010

  20. Bjorken sum rule from neutron β decay Savin Fest, Dubna, 7.12.2010

  21. Gluon polarization from PGF (LO) Data not yet in global fits Savin Fest, Dubna, 7.12.2010

  22. Transverse spin structure Savin Fest, Dubna, 7.12.2010

  23. TMD parton distributions aka Sivers Transversity Boer– Mulders • 8 intrinsic transverse-momentum dependent PDFs at LO • Azimuthal asymmetries with different angular modulations in the hadron and spin azimuthal angles, Φh and Φs Savin Fest, Dubna, 7.12.2010

  24. Proton Collins asymmetry p Fit to COMPASS d, HERMES, BELLE (Collins FF, e+e-) in good agreement with new proton data Savin Fest, Dubna, 7.12.2010

  25. Proton Sivers asymmetry h+ h− • compatible with zero for the deuteron • non-zero asymmetry for pos. hadrons Savin Fest, Dubna, 7.12.2010

  26. What’s next: COMPASS-II • PolarisedDrell-Yan • Generalized Parton Distributions (GPD) • Pion (and kaon) Polarisabilities recommended by Programme Committee (SPSC) Savin Fest, Dubna, 7.12.2010

  27. Pion Polarisabilityexperimental situation  -  Planned measure-ment better thanχPT-prediction. Strong JINR parti-cipation

  28. PDF, GPD, TMD PDF GPD TMD Ji, PRL 2003, Belitsky, Ji, Yuan PRD 2004 Meissner, Metz, Schlegel, JHEP 0908:056 2009 Savin Fest, Dubna, 7.12.2010

  29. Generalized Parton Distribution Functions ~ ~ • Novel concept, universal, H, H, E, E • H (E) nucleon helicity (non)conservation • Nucleon form factors and PDFs as limiting cases • Correlating transverse spatial and longitudinal momentum degrees of freedom (‘tomography’) • DVCS & DVMP Total orbital momentum: x is not x-Bjorken X.-D. Ji, Phys. Rev. Lett. 78 (1997) 610 Savin Fest, Dubna, 7.12.2010

  30. GPDs need ECAL0 • ECAL0 essential for GPD programme • led by JINR, promising novel technology MAPDs • looking forward for another decade of fruitful collaboration with JINR & Igor Savin Fest, Dubna, 7.12.2010

  31. EoR 2001 Savin Fest, Dubna, 7.12.2010

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