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Klaus Rith University of Erlangen-Nürnberg

New Results. Klaus Rith University of Erlangen-Nürnberg. HERA Symposium 2011 July 5, 2011. Main HERMES research topics:. Origin of nucleon spin. Details of nucleon structure.

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Klaus Rith University of Erlangen-Nürnberg

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  1. New Results Klaus Rith University of Erlangen-Nürnberg HERA Symposium 2011 July 5, 2011

  2. Main HERMES research topics: Origin of nucleonspin Details of nucleonstructure Quark Properties: fractionalcharge spin-1/2 longitudinal momentumxP intrinsictransversemomentumpT spatialpositionr orbital angular momentum L 2

  3. Atom (non-relativistic electrons in Coulomb potential) Rutherford Bohr, Schrödinger, .. Add angular momentum n, l, ml(r,,) 3

  4. Nucleon (Relativisticquarks in colourfield) Inclusive DIS r Add angular and transverse momentum Wigner DF W(pT,r) TMDs GPDs Number density of quarks with longitudinal momentum fraction x (pT-dependence) (r-dependence) 4

  5. Accessing the nucleon‘s structure inclusive DIS Integrated DFs 1D exclusive reactions semi-inclusive DIS 3D 3D GPDs TMDs theory after G. Schnell 5

  6. TMDs Accessible in inclusive DIS Quarkpolarisation T N/q U L f1 h1 U Number Density Boer-Mulders Nucleon structure described by 8 leading-twist (+ many subleading) quark distributions containing information about quark orbital motion and spin-orbit effects Nucleonpolarisation g1 h1L L Helicity Mulders-Kotzinian h1 g1T T Transversity Sivers Worm-gear h1T Pretzelosity 6

  7. Inclusive Measurements 7

  8. Longitudinal double-spin asymmetry: g1,  old P.R. D 75 (2007) 012007 g1(x) = ½eq2q(x) q  = 0,330 ± 0,025 ± 0,011 ± 0,028 (from 1d) q(x) = q (x) – q (x) MS (exp) (theory) (evol.) q = q(x) dx  = 0,12 ± 0,09 ± 0,14 (from 1p) EMC, P.L. B 206 (1988) 364 1 = g1(x) dx   q q new g/g = 0,045 ± 0,034 ± 0,126 (high-pT hadrons) HERMES, JHEP 08 (2010) 130 Furthermore: 8

  9. Unpolarised DIS cross section: F2 From global fit: HERMES relative normalisation ~2% for p and d and ~0.5% for the ratio Exploring perturbative to non-perturbative regime in an unmeasured x-Q2 region 0.006 < x < 0.9 0.1 GeV2 < Q2 < 20 GeV2 new JHEP 05 (2011) 126 Ratio d/p (F2d/F2p) Proton Deuteron New region covered by HERMES Good agreement with world data in the overlap region 9

  10. Semi-inclusive Measurements 10

  11. Semi-inclusive Deep-Inelastic Scattering z = Eh/ eqeq  FactorisationeNehX = DFNq FFqh DF(x,Q2): Parton Distribution Function – q(x,Q2)  f1q(x,Q2), q(x,Q2)  g1q(x,Q2), q(x,Q2) )  h1q(x,Q2), … FF(z,Q2): FragmentationFunction – D1qh(z,Q2), H1qh(z,Q2), … 11

  12. Charged-hadron multiplicities I Proton-deuteron asymmetry UU  f1q  D1qh LO interpretation: Reflects different flavor content Correlated systematics cancel new new Disagreement Disagreement 12

  13. Charged-hadron multiplicities II UU  f1q  D1qh Disentanglement of z and Ph dependences Access to intrinsic quark pT and fragmentation kT <Ph2> = z2<pT2> + <kT2> new new Ph Ph 13

  14. Double-spin asymmetry A1h LL  g1q  D1qh Refined studies extending the work in Phys. Rev. D 71 (2005) 012003 With charge conjugation symmetry in fragmentation D1,qh+ = D1,qh- uv + dv new A1d h+-h- = (x) uv + dv new x x x x Integral over sum of valence distributions compatible with  Sea contribution to nucleon spin small x x 14

  15. Leading-twist TMDs Nucleon structure described in leading-twist by 8transverse-momentum dependent quark distributions (TMDs) HERMES has access to all of them through specific azimuthal modulations (, s) of the cross section thanks to the polarised beam and target d6 dx dy dz d ds dP2h cos2 sin2 sin(+s) sin(3-s) sin(-s) cos(-s) Chiral-oddDFs, needchiral-oddFF: H1,qh 15

  16. Leading-twist TMDs Pioneering measurements by HERMES Quarkpolarisation T N/q U L Indication to be non-zero! Preliminary result h1 f1 U Number Density Boer-Mulders Consistent with zero PLB 562 (2003) 182 PRL 84 (2000) 4047 Nucleonpolarisation g1 h1L L Different from zero PRL 94 (2005) 012002 PLB 693 (2010) 11 Helicity Mulders-Kotzinian new h1 g1T T Transversity Sivers Worm-gear Consistent with zero Preliminary result h1T Pretzelosity Different from zero PRL 94 (2005) 012002 PRL 103 (2009) 152002 Small Preliminary result 16

  17. sT pT pT sT Boer-Mulders DF h1,q      UU cos2 h1,q  H1,qh transversely polarised quarkswith pTin unpolarised nucleon h1 is chiral-odd and naive T-odd (like f1T) requires FSI/ISI new Opposite sign for + and -, larger magnitude for - h1,u and h1,d have same sign Large signal with same sign for K sea fragmentation important 17

  18. Worm-gear DF g1T,q longitudinally polarised quarksin transversely polarised nucleon      LT cos(-s) g1T,q  D1qh new Related to parton orbital motion: requires interference between wave functions with OAM difference by 1 unit Slightly non-zero g1T,q = - h1L,q (supported by many models) 1 dy g1T,q x  g1q(y) (Wandzura-Wilczek type approximation) y x 18

  19. Exclusive Measurements 19

  20. Generalised parton distributions Generalisation of Form Factors (moments of GPDs) and PDFs (forward limit) Correlated information about longitudinal momentum xp and transverse spatial position r Ji relation: Jq=1/2 + Lq= lim dx x [H(x,,t) + E(x,,t)] t0 Final state sensitive to different GPDs Spin-½ target: 4 chiral-even leading-twist quark GPDs H,H (E,E) conserve (flip) nucleon helicity Vector mesons (, , ) H, E Pseudoscalar mesons(,) H, E DVCS () H, E, H, E Access: exclusive processes ~ ~ ~ ~ ~ ~ 20

  21. Hard exclusive 0-meson production I Photon SDMEs Meson SDMEs EPJC 62 (2009) 659 Helicity amplitudes FV= TV + UV EPJ C 71 (2011) 1609 new Helicity amplitudes are the fundamental quantities to be compared with theory They form a basis for the SDMEs Re-derived SDMEs consistent with published ones Enhanced sensitivity for polarised SDMEs 21

  22. Hard exclusive 0-meson production II Hierarchy predicted by theory, confirmed by HERMES LL TT TL LT Large (as for H1) EPJ C 71 (2011) 1609 new expected small by GPD models tan(11) = Im(t11)/Re(t11) 1/Q dependence expected from pQCD Sizeable UPE 22

  23. Deeply Virtual Compton Scattering & GPDs Theoretically cleanest way to access GPDs Interference between DVCS and Bethe-Heitler amplitude TDVCS << TBH@ HERMES AXY Access to GPD combinations through azimuthal asymmetries beam target polarisation HERMES: Complete set of asymmetries Bothbeam charges Both beam helicities Unpolarised H,D and nuclear targets Longitudinally polarised H and D targets Transversely polarised H target 23

  24. DVCS asymmetries measured @ HERMES Beam chargeasymmetry GPD H H: PRL 87 (2001) 182001 PR D 75 (2007) 011103 JHEP 11 (2009) 083 D: Nucl. Phys. B 829 (2010) 1 Beam helicityasymmetry GPD H Transverse target-spinasymmetry GPD E H: JHEP 06 (2008) 066 Transverse double-spinasymmetry GPD E new H: arXiv:1106.2990 Longitudinal targetspinasymmetry GPD H ~ H: JHEP 06 (2010) 019 D: Nucl. Phys. B 842 (2011) 265 new Longitudinal double spinasymmetry GPD H ~ 24

  25. DVCS: transverse target asymmetry AUT Sensitive to GPD E old JHEP 06 (2008) 066 Model: VGG with variation of Ju, while Jd=0 25

  26. DVCS transverse double-spin asymmetry ALT Beam polarisation Target polarisation Beam charge  arXiv:1106.2990 new Sensitive to both GPDs entering the Ji sum rule Consistentwithzero, cancellationsbetween E and H Sensitivityto Jusuppressedbykinematicfactors 26

  27. DVCS with Recoil Detector Recoil Detector to tag exclusivity ep ep 1 T SC Solenoid Photon Detector Scintillating Fiber Tracker Silicon-Strip Detector Unpolarised H and D targets 27

  28. DVCS with Recoil Detector 28

  29. Pure elastic DVCS new Indicationthatleadingamplitudefor pure elasticprocessisslightly larger thanforunresolvedsignal (elastic + associated) 29

  30. DVCS with RD  Helicityamplitudes F2 Worm-gear DF x(uV +dV) Boer-Mulders DF HadronMultiplicities 30

  31. Backups

  32. Pure elastic DVCS new Indicationthatleadingamplitudefor pure elasticprocessisslightly larger thanforunresolvedsignal (elastic + associated)

  33. Double-spin asymmetry A1h LL  g1q  D1qh Refined studies extending the work in Phys. Rev. D 71 (2005) 012003 A1h(x,Ph) 2D - dependencies new Sensitive to differences in transverse momentum dependence of g1 and f1 No significant Ph dependence observed Ph 14

  34. Transversity, Collins Amplitudes TransversityDF  2sin( + S)hUT h1q(x)  H1q(z)    CollinsFF arXiv:1006.4221 proton Both Collinsfragmentation function and transversity distribution function are sizeable Surprisingly large - asymmetry Possible source: large contribution (with opposite sign) from unfavored fragmentation, H1 ,disf - H1 ,fav

  35. Extraction of Transversity Fit to HERMES (ep ->ehX), COMPASS (d ->hX), BELLE (e+e- ->h+h-X) data M.Anselmino et al., Nucl. Phys. Proc. Suppl. 191 (2009) 98 xu(x) xu(x) xd(x) xd(x)

  36. Sivers Amplitudes for Pions SiversDF  2sin( - S)hUT  f1T,q(x) D1q(z)    PRL 103 (2009) 152002 First observationof non-zeroSiversDFinDIS proton Rise at low Ph, plateau at high Ph Clear rise with z Non-zero at low x Experimental evidence for orbital angular momentum Lqofquarks But: Quantitative contributionofLqtonucleonspinstillunclear

  37. Sivers distribution Fit to HERMES (ep -> ehX) and COMPASS (d -> hX) data M.Anselmino et al., Phys. Rev. D79 (2009) 054010 Lattice Orbital angular momenta ofupand down quarkshaveoppositesign -xf 1T(x) Ld  -L u  0.2 Ld + d/2  0 !?? x

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