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Recent results from lepton proton scattering on the spin structure of the nucleon

Recent results from lepton proton scattering on the spin structure of the nucleon. Hall B. Hall A. Two high-resolution 4 GeV spectrometers. Large acceptance spect. electron/photon beams. Beam: 160 GeV m ; 75% polarization Target: 6 LiD; 50% polarization. Hall C.

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Recent results from lepton proton scattering on the spin structure of the nucleon

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  1. Recent results from lepton proton scattering on the spin structure of the nucleon

  2. Hall B Hall A Two high-resolution 4 GeV spectrometers Large acceptance spect. electron/photon beams Beam: 160 GeV m; 75% polarization Target: 6LiD; 50% polarization Hall C Beam: 27.5 GeV e±; <50>% polarization Target: (un)-polarized gas targets; <85%> polarization Beam: ≤6 GeV e-; 85% polarization Target: polarized targets 3He, 6LiD, NH3 7 GeV spectrometer, 1.8 GeV spectrometer, large installation experiments The contemporary experiments

  3. Naïve parton model Unpolarised structure fct. Gluons are important ! BUT Full description of Jq and Jg needs orbital angular momentum 1989 EMC measured S = 0.120 0.094 0.138 ± ± DG Spin Puzzle Sea quarksDqs News on the spin structure of the nucleon

  4. FF DF Deep Inelastic Scattering Important kinematic variables: q cross section: Spin 1

  5. How to measure Quark Polarizations • Virtual photon g* can only couple to quarks of opposite helicity • Select q+(x) or q-(x) by changing the orientation of • target nucleon spin or helicity of incident lepton beam Asymmetry definition: inclusive DIS: only e’ info used semi-inclusive DIS: e’+h info used

  6. (Hall-A) Proton Deuterium A1n from 3He CLAS PLB 641, 11 (2006) COMPASS PRD75(2007)012007 World data on inclusive DIS • New data from COMPASS, • HERMES & JLab very precise • high x-behaviour consistent with • A1 with x1 • A1d consistent with zero • for x < 0.05

  7. World data on inclusive DIS Combine p and d to get n: or 3He • What can we learn on the PDFs Compass: hep-ex/0609038 Hermes: hep-ex/0609039

  8. Q2=5 GeV2, NNLO in MS scheme HERMES: Integrals • Saturation in deuteron integral is assumed • use only deuterium From hyperon beta decay a8=0.586±0.031 From neutron beta decay a3=1.269±0.003 • COMPASS:

  9. CLAS: Dq • Using:

  10. In LO-QCD: Polarised quark distributions Correlation between detected hadron and struck qf “Flavor – Separation” Inclusive DIS: Semi-inclusive DIS:

  11. COMPASS: Valence PDFs • For LO: • Assuming: • Gv is 2.5sstat away from flavour • symmetric sea scenario

  12. In LO-QCD: MC Polarised quark distributions Correlation between detected hadron and struck qf “Flavor – Separation” Inclusive DIS: Semi-inclusive DIS: Extract Dqby solving:

  13. Du(x), Dd(x) ~ 0 • In measured range (0.023 – 0.6) • No indication forDs(x)<0 Polarised opposite to proton spin Polarised parallel to proton spin Polarized Quark Densities • First complete separation of • pol. PDFs without assumption on • sea polarization Dd(x) < 0 • Du(x) > 0 good agreement with NLO-QCD

  14. c2DIS c2SIDIS Duv Ddv Du Dd Ds Dg DS Kretzer -0.049 -0.051 206 225 0.94 -0.34 -0.055 0.68 0.28 KKP -0.11 -0.045 0.57 206 231 0.70 -0.26 0.087 0.31 NLO FIT to DIS & SIDIS Data D. De Florian et al. hep-ph/0504155 NLO @ Q2=10 GeV2 • SIDIS data improves description of allDq, especially light sea • Kretzer FF favor SU(3) symmetric sea, not so for KKP • DS ~30%in all cases

  15. DG>0 DG>0 DG<0 DG<0 Several more fits • using mainly only inclusive data or a combination of inclusive and • some semi-inclusive data • Results for DG still completely all over the place • Need a consistent approach for fit and uncertainty determination • with all world data taken into account Lets measure DG more directly

  16. Isolate the photon gluon fusion process (PGF) • Open Charm production • Reaction: LO-MC: Aroma The golden channels Idea: Direct measurementofDG

  17. + + + .. less sub-processes contributing  h±h± higher statistics  more sub-processes contributing  q q higher statistics  qg less sub-processes contributing  g h± g more sub-processes contributing  The golden channels Idea: Direct measurement ofDG Isolate the photon gluon fusion process • detection of hadronic final states with high pT • high pT pairs of hadrons • single high pT hadrons • Several possible contributions to the measured asymmetry • MC needed to determine R and aLL Important at Q2<0.1

  18. Dg/g=0.016±0.058(stat.)±0.055(syst.) m2=3.0GeV2 10% of statistics COMPASS Results h±h± • Channel: • Cuts: Q2 > 1 GeV2 • RPGF = 0.34 +/- 0.07 xF > 0.1 z > 0.1 m(h1,h2) > 1.5 GeV 2(scale) ~ 3 GeV2<xG> ~ 0.13 Q2 < 1 GeV2 & used for Dg/g extraction

  19. HERMES Results Subprocess Fractions h±h±, h± • Channels: Subprocess Asymmetries (using GRSV std.)

  20. World Data on DG/G x Long way to go till Dg(x)

  21. exclusive: all products of the reaction are detected missing energy (DE) and missing Mass (Mx) = 0 from DIS: ~0.3 The Hunt for Lq Study of hard exclusive processes leads to a new class of PDFs Generalized Parton Distributions possible access to orbital angular momentum

  22. unpolarized polarized quantum numbers of final state select different GPD vector mesons pseudo-scaler mesons DVCS AUT,sr,F,w AUT,sp+ AC,ALU,AUT, AUL GPDs Introduction What does GPDs charaterize? conserve nucleon helicity flip nucleon helicity not accessible in DIS

  23. HERMES / JLAB kinematics: BH >> DVCS p + D DVCS Bethe-Heitler (BH) isolate BH-DVCS interference term non-zero azimuthal asymmetries DVCS two experimentally undistinguishable processes:

  24. ~ DsC~cosf∙Re{ H+ xH +… } ~ DsLU~sinf∙Im{H+ xH+ kE} DsUT polarization observables: ~ DsUL~sinf∙Im{H+ xH+ …} beam target DVCS ASYMMETRIES  different charges: e+ e-(only @HERA!): H H ~ H DsUT~sinf∙Im{k(H- E) + … } H, E kinematically suppressed x = xB/(2-xB ),k = t/4M2

  25. <-t> = 0.18 GeV2 <-t> = 0.30 GeV2 <-t> = 0.49 GeV2 <-t> = 0.76 GeV2 CLAS: DVCS - BSA Accurate data in a large kinematical domain Integrated over t

  26. Neutron obtained combining • deuterium and proton • F1 small u & d cancel in Away to E and Ju-Jd Hermes DVCS-TTSA: Hall A nDVCS-BSA: x=0.36 and Q2=1.9GeV2

  27. Can we constrain (Ju - Jd) • first model dependent extraction of Ju - Jd possible • VGG-Code: GPD-model: LO/Regge/D-term=0

  28. std. FF Sivers DFF quarks left left left  photon proton photon right right right Access to Lq in semi-inclusive scattering • New structure function accessible with SSA Side view Front view • The presence of spin can distort the distribution of quarks in transverse space (orbital angular momentum of quarks is required) NOTE: QCD tells us that the FSI has to be attractive, since quark and remnants form a color antisymmetric state • A distortion in the distribution of quarks in transverse space can give rise to a nonzero Sivers function

  29. HERMES & COMPASS Measuremnets • Proton: • Sivers moment: • p+ > 0 p- ~ 0 • K+ > 0 K- ~ 0 • K+ > p+ • sea quarks important • Deuterium ~ 0 • u and d quark cancel Deuterium Proton

  30. Results from theory Lattice QCD: Sivers Pheno. analysis from data: negative for up quarks Anselmino et al., hep-ph/0511017 [20] Anselmino et al., PRD72 (05) [21] Vogelsang, Yuan, PRD72 (05) [23] Collins et al., hep-ph/0510342 positive for down quarks QCDSF/UKQCD Collab. (hep-ph/05110032)

  31. DG Lq Dq Dq dq Lg Lq Lg DG dq Summary

  32. Spin is fascinating Thank you for your attention

  33. BACKUP SLIDES

  34. angle of hadron relative to initial quark spin (Sivers) peculiarity of f^1T chiral-even naïve T-odd DF related to parton orbital momentum violates naïve universality of PDF (Sivers) (Collins) different sign of f^1T in DY Azimuthal angles and asymmetries angle of hadron relative to final quark spin (Collins)

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