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Spin structure of the nucleon

Spin structure of the nucleon. Delia Hasch. introduction to polarised DIS. prerequisites. quark polarisation. gluon polarisation. the (spin) structure of the nucleon. N. Bohr. W. Pauli.

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Spin structure of the nucleon

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  1. Spin structure of the nucleon Delia Hasch • introduction to polarised DIS • prerequisites • quark polarisation • gluon polarisation • the (spin) structure of the nucleon

  2. N. Bohr W. Pauli preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 fascinatedby spin …. “You think you understand something? Now add spin…”-- R. Jaffe

  3. Pauli : exclusion principle preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 what is spin ? [www.markusehrenfried.de/science/physics/whatisspin.html] • Stern-Gerlach (1921): • Uhlenbeck, Goudsmit: • (1925) • explanation of atomic spectra quantum number: ms=1/2

  4. “deep” high resolution: • “inelastic” preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 how to study the nucleon structure ? … deep-inelastic scattering (DIS)  Q2 determines the resolution  nucleon has a structure

  5. gluons are important ! don’t forget the orbital angular momentum! • DG • sea quarks: Dqs Spin Puzzle preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 the nucleon spin structure QPM: EMC 1988: DS=0.123 ± ... SLAC, CERN, DESY: DS 0.2-0.4

  6. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 helicity densities Dq because of helicity conservation, the virtual photon can couple only to a quark of opposite helicity by changing the orientation of target nucleon spin or the helicity of incident lepton beam we can select q+(x) or q-(x) Dq

  7. Stern-Gerlach separation self-polarised electrons: e • resolution: dp/p~2%, dq<1 mrad • particle ID: lepton ID with e~98%, hadron contamination <1% • RICH: p, K, p ID within 2<Eh<15 GeV 27.5 GeV (e+/e-) <Pb>~ 0.53±0.03 preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 experimental prerequisites (Hermes) Stern-Gerlach separation pure nuclear-polarised atomic gas, flipped at 90s time intervals, <Pt>~0.85 ±0.04

  8. leptonic part of the cross section  independent of nucleon structure  can be calculated explicitely hadronic part of the cross section  contains information on nucleon structure  cannot be calculated from first principles preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 DIS cross section

  9. QPM: momentum distribution of quarks preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 helicity distribution of quarks hadronic tensor • parametrised by structure functions (symmetry considerations, conservation laws)

  10. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 how to measure cross sections /asymmetries q = const. E’ = const.

  11. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 quark helicity distributions

  12. Dq and DG from inclusive data (QCD fit) parameterised minimisation : evaluate parameters preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 one step further (evolution equations):

  13. Duv and Ddv (quite) well determined: • Duv >0,Ddv <0 • Dq and DG weakly constraint by data preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 Dq and DG from inclusive data

  14. unpolarised DIS need polarised collider to extend kinematic coverage • need more direct probes preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 how to further proceed ? • Dq and DG from inclusive DIS data: via evolution equations • requires wide kinematic range in Q2 and x • only fixed target spin experiments so far …

  15. probability that struck quark of flavour f fragments into hadron of type h with energy fraction z flavour tagging p+ ud K- us p- ud fragmentation function distribution function , z=Eh/n preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 polarised semi-inclusive DIS

  16. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 polarised quark distributions • flavour separation by flavour tagging flavour content of final state hadrons related to flavour of struck quark via fragmentation functions Dqh not well known at √s~5-20 GeV of current polarised DIS experiments 

  17. p+ h+ K+ p- h- K- K- us all sea objects preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 measured hadron asymmetries proton HERMES incl p+ h+ deuteron HERMES p- incl h- h- p- x x

  18. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 purities probability that g* hit a quark of flavour q when hadron of type h wasdetected u u d d s s p+ K+ p- K-

  19. sea quarks (u, d, s ,s) compatible with 0 - - - first direct 5-flavour separation of polarised PDFs new data from COMPASS/RHIC coming preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 quark/anti-quark helicity distributions [HERMES, PRL92(2004), PRD71(2005)] u quarks large positive polarisation d quarks negative polarisation

  20. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 how to measure the gluon polarisation DG …reminder: from scaling violation

  21. D g* c c c D g preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 direct measurement of DG method: photon-gluon fusion q q t  ħ/2mq • open charm production (hard scale: mass of c-quark)  theoretically very clean:  experimentally very challenging:  vertex reconstruction inside massive target  S/B

  22. h1 h2 g* g preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 direct measurement of DG method: photon-gluon fusion q q t  ħ/2mq • hadron pairs with high transv. momenta (hard scale: PT)  experimentally very clean  highly model dependent

  23. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 Gfrom high-pT hadron pairs 3 main contributions to*ph+h-X : h2 h2 h2 * q q * * q V q g p g q q h1 h1 QCDC VMD PGF h1 AQCDC~q/q AVDM= 0 APGFG/G • estimate their relative contributions: Monte Carlo… 0.5 -1

  24. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 Gfrom high-pT hadron pairs 3 main contributions to*ph+h-X : h2 h2 h2 * q q * * q V q g p g q q h1 h1 QCDC VMD PGF h1 AQCDC~q/q AVDM= 0 APGFG/G [PRL84(2000)]

  25. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 Gfrom high-pT hadron pairs first glimpse:

  26. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 Gfrom high-pT hadron pairs first glimps: complementary measurement @RHIC

  27. STAR preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 Gfrom p0 at RHIC pp p0X is sensitive to gg gg and gq gq

  28. uncertainty still large ... • dramatic improvement by lumi and • beam polarization (~70%) preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 Gfrom p0 at RHIC pp p0X is sensitive to gg gg and gq gq fractional contributions:

  29. preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 futureGmeasurements (2010) COMPASS :  open charm  high PT first glimps: HERMES :  high PT on d RHIC :  p0  jets  prompt g  charm/bottom

  30. the nucleon puzzle is going to be completed transversity HERMES COMPASS RHIC JLab KEK …ecc. exclusive processes first results: HERMES JLab preface| introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Haschspin structure of the nucleon GK: Freiburg-University 06/07/05 where do we stand the (spin) structure of the nucleon … HERMES: first glimpse NMC,BCDMS,E665, H1, ZEUS COMPASS RHIC ? HERMES (SMC, SLAC)  Compass  RHIC seminar by its own ? seminar by its own

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