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The Quest for the spin of the proton ! or

The Quest for the spin of the proton ! or. “You think you understand something? Now add spin…” - R. Jaffe. The Spin of the Proton. Nobel Prize, 1943: "for his contribution to the development of the molecular ray method and his discovery of the magnetic moment of the proton" .

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The Quest for the spin of the proton ! or

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  1. The Quest for the spin of the proton ! or “You think you understand something? Now add spin…” - R. Jaffe DIS - Madrid, April 2009

  2. The Spin of the Proton Nobel Prize, 1943: "for his contribution to the development of the molecular ray method and his discovery of the magnetic moment of the proton" mp = 2.5 nuclear magnetons, ± 10% (1933) Proton spins are used to image the structure and function of the human body using the technique of magnetic resonance imaging. Otto Stern Sir Peter Mansfield Paul C. Lauterbur Nobel Prize, 2003: "for their discoveries concerning magnetic resonance imaging" DIS - Madrid, April 2009

  3. DG SqLq Lg SqDq SqDq Lg SqLq dq DG dq How do the partons contribute Is the proton looking like this? gluon spin “Helicity sum rule” Where do we stand solving the “spin puzzle” ? angular momentum total u+d+s quark spin DIS - Madrid, April 2009

  4. γ* u,d,s,g γ* p,K u,d,s p,K jet u,d,s,g u,d,s,g u,d,s,g Dq & DG contributions to the proton spin Existing data from: polarized SIDIS Dqf polarized DIS SqDq, DG • to extract polarized PDFs • !a “global QCD analysis” is required ! • all processes tied together: • universality of pdfs & Q2 – evolution • each reaction provides insights into • different aspects and kinematics • in NLO • DSSV PRL101:072001,2008 polarized pp scattering Dqf, DG DIS - Madrid, April 2009

  5. Inclusive World data • Inclusive DIS-Data: new : input to the old GRSV-analysis : input to the DIS & SIDIS – analysis by DNS DIS - Madrid, April 2009

  6. Semi-Inclusive World Data • Semi-inclusive DIS-Data: not in DNS DIS - Madrid, April 2009

  7. c2DIS c2SIDIS Duv Ddv Du Dd Ds Dg DS Kretzer -0.049 -0.051 206 225 0.94 -0.34 -0.055 0.28 KKP -0.11 -0.045 206 231 0.70 -0.26 0.087 0.31 0.813 -0.458 0.036 -0.115 -0.057 0.242 DSSV NLO FIT to World Data NLO @ Q2=10 GeV2 D. De Florian et al. arXiv:0804.0422 • includes all world data from DIS, SIDIS and pp • Kretzer FF favor SU(3) symmetric sea, not so for KKP, DSS • DS ~25-30%in all cases DIS - Madrid, April 2009

  8. Polarized Strangeness Driven by SIDIS K-Asymmetries K-FF dominated by New Results from isoscaler method AK++K- & Aincl “Purity” Method using FF Driven by SU(3); (3F-D) Results are completely consistent with Hermes sea quark polarizations ~ 0 DIS - Madrid, April 2009

  9. dotted: CTEQ-6L & fit dashed: Fit x-dependence of multiplicities using PDFs from CTEQ-6 More on Strangeness PDF • Kaon multiplicities from Deuterium target • strange quark sea in proton and neutron identical • fragmentation simplifies • Only assumptions used: • isospin symmetry between proton and neutron • charge-conjugation invariance in fragmentation dashed-dotted: solid: S(x)= Q(x): CTEQ-6L & DSS s(x) + sbar(x) DIS - Madrid, April 2009

  10. The Gluon Polarization RHIC: many sub-processes with a dominant gluon contribution high-pT jet, pion, heavy quark, … in NLO unpolarised cross sections nicely reproduced in NLO pQCD DIS - Madrid, April 2009

  11. STAR RHIC Data GRSV curves with cone radius 0.7 and -0.7 <  < 0.9 2005 jet data: PRL 100, 232003 (2008) p0 @ 200 GeV 2005:PRD 76, 051106 2006: arXiv:0810.0694 DIS - Madrid, April 2009

  12. x small-x 0.001· x · 0.05 RHIC range 0.05·x· 0.2 large-x x¸ 0.2 The Gluon Polarization • Dg(x) very small at medium x • best fit has a node at x~0.1 • huge uncertainties at small x • small-x behavior completely • unconstrained Dg(x) small !? DIS - Madrid, April 2009

  13. + + + .. 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  Compass & Hermes: The golden channels for Dg Idea: Direct measurement ofDG Isolate the photon gluon fusion process • detection of hadronic final states • charmed mesons • high pT pairs of hadrons • single high pT hadrons • Several possible contributions to the measured asymmetry • MC needed to determine R and aLL h±h±vs. h±: h±more inclusive → pQCD NLO calculations (easier) possible Important at Q2<0.1 DIS - Madrid, April 2009

  14. Dg from electro production DSSV gluon agrees well with model-dependent “LO” extractions of Dg/g not in global fit [NLO not available] a future global NLO fit will use measuredALLnot derived Dg/g need first to check unpolarized cross section DIS - Madrid, April 2009

  15. X. Ji, D. Mueller, A. Radyushkin (1994-1997) Proton form factors, transversecharge & current densities Structure functions, quark longitudinal momentum & helicity distributions Beyond form factors and quark distributions Generalized Parton Distributions Correlated quark momentum and helicity distributions in transverse space - GPDs DIS - Madrid, April 2009

  16. How to access GPDs? quantum number of final state selects different GPDs: • theoretically very clean • DVCS(g):H, E, H, E • VM(r, w, f):H E • info on quark flavors • PS mesons(p, h):H E ~ ~ ~ ~ DIS - Madrid, April 2009

  17. VM production @ small x W &t dependences: probe transition from softhard regime r f J/Y U s ~ Wd s ~ e-b|t| steep energy dependence of s in presence of the hard scale universality of b-slope parameter: point-like configurations dominate DIS - Madrid, April 2009

  18. p + D DVCS Bethe-Heitler (BH) isolate BH-DVCS interference term non-zero azimuthal asymmetries Deeply Virtual Compton Scattering DVCS most clean channel for interpretation in terms of GPDs HERMES / JLAB kinematics: BH >> DVCS two experimentally undistinguishable processes: can measure DVCS – cross section and I DIS - Madrid, April 2009

  19. DVCS HERMES: combined analysis of charge & polarization dependent data  separation of interference term + DVCS2 Beam Spin Asymmetry DVCS Beam Charge Asymmetry higher twist higher twist DIS - Madrid, April 2009

  20. DVCS from & Archiv: 0812.2517 only some appetizers on existing data lets see what theory says DIS - Madrid, April 2009

  21. Results from Theory Lattice: K. Kumericki & D. Mueller arXiv: 0904.0458 contribution to nucleon spin CLAS BSA Hermes BCA First hints for a small JqLq Hall A Hall A mp2 GeV2 different GPD parametrisations LHPC Collab. hep-lat/0705.4295 t=0 t=-0.3 DIS - Madrid, April 2009

  22. More insights to the proton - TMDs Explore spin orbit correlations Single Spin Asymmetries Unpolarized distribution function q(x), G(x) Transversity distribution function dq(x) Siversdistribution function Boer-Muldersdistribution function Correlation between and Helicity distribution function Dq(x), DG(x) peculiarities of f^1T chiral even naïve T-odd DF related to parton orbital angular momentum violates naïve universality of PDFs QCD-prediction: f^1T,DY = -f^1T,DIS Correlation between and Correlation between and DIS - Madrid, April 2009

  23. Transverse Polarization Effects @ RHIC • Naive pQCD (in a collinear picture) predicts AN ~ mq/sqrt(s) ~ 0 Left -Right However, large ANobserved in forward pions / Kaons. Proposed mechanisms - Sivers - Collins - twist-3 process - ... need correlations between particles (g-jet) to disentangle underlying process DIS - Madrid, April 2009

  24. Boer-Mulders Unpol. SIDIS cross section: Boer-Muldersx Collins FF • remember Collins FF: Boer-Muldersfct. for u and d quark seem to have same sign consistent with Fermi-lab DY-experiments E605++ DIS - Madrid, April 2009

  25. HERMES & COMPASS Measurements • Proton: • Sivers moment: • p+ > 0 p- ~ 0 • K+ > 0 K- ~ 0 • K+ > p+ • importance of sea quarks? • Deuterium ~ 0 • u and d quark cancel hep-ex/0802.2160 Deuterium Proton Fit M. Anselmino et al. arXiv:0805.2677 DIS - Madrid, April 2009

  26. Sivers function and OAM Model dependent statement: Siversfct. from fit to M. Burkardt et al. anomalous magnetic moment: ku = 1.67 kd = -2.03 Lattice: P. Haegler et al. lowest moment of distribution of unpol. q in transverse pol. proton and of transverse pol. quarks in unpol. proton x Anselmino et al. arXiv:0809.2677 DIS - Madrid, April 2009

  27. we have just explored the tip of the iceberg you are here Du, Dd Conclusions Dutot, Ddtot many avenues for further important measurements and theoretical developments Dg Ds Lq,g Thank you for your attention & to everybody, who helped preparing the talk, especially Werner and Marco spin sum rule DIS - Madrid, April 2009

  28. BACKUP SLIDES DIS - Madrid, April 2009

  29. 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 DIS - Madrid, April 2009

  30. DSS: good global fit of all e+e-, ep, and pp hadron data main results: de Florian, Sassot, MS • results for p±, K±, chg. hadrons • full flavor separation for DiH(z) andDgH • uncertainties (L.M.) well under control • fits all LEP, HERMES, SMC, RHIC, … data • supersede old fits based only on e+e- data DIS - Madrid, April 2009

  31. accessing GPDs: some caveats but only x and t accessible experimentally xis mute variable (integrated over): • apart from cross-over trajectory (x=x)GPDs not directly • accessible: deconvolution needed ! (model dependent) GPD moments cannot be directly revealed, extrapolationst0are model dependent e.g. t=0 q(x) x=0  q(x) cross sections & beam-charge asymmetry ~ Re(TDVCS ) beam or target-spin asymmetries ~ Im(TDVCS ) DIS - Madrid, April 2009

  32. RHIC pp data (BRAHMS, STAR)explain different Dg smaller u & larger s-frag. required by SIDIS note: some issues with K- data (slope!) await eagerly final HERMES data detour: DSS kaonFF’sDiK(z) DIS - Madrid, April 2009

  33. ~ 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 DIS - Madrid, April 2009

  34. probing partons with specified long. momentum @transverse position b T What does theory tell [M. Burkardt, M. Diehl 2002] FT (GPD) : momentum space  impact parameter space: polarized nucleon: u-quark d-quark [x=0] from lattice DIS - Madrid, April 2009

  35. Hermes: Charge and Beam Spin Asymmetry Heavy Targets Beam Charge Asymmetry Beam Spin Asymmetry • Why nuclear DVCS: • constrain nuclear GPDs • constrain models attempting • to describe nuclear matter • neutron and proton matter • distribution in nuclei DIS - Madrid, April 2009

  36. 160 GeVμ SM2 SM1 6LiD Target The contemporary experiments Trigger-hodoscopes μFilter ECal & HCal 50 m STAR Detector Beams: √s=200 GeV pp; 50% polarization Lumi: 50 pb-1 RICH MWPC Beam: 27.5 GeVe±; <50>% polarization Target: (un)-polarized gas targets; <85%> polarization Lumi: pol: 5x1031 cm-2/s-1; unpol: 3x1032-33 cm-2/s-1 Data taking finished June 2007 Straws Gems Drift chambers Beam: 160 GeVm: 80% polarization Target: 6LiD: 50% polarization (2002-2006) NH3: 80% polarisation (2007) Lumi: 5x1032 cm-2s-1 Micromegas Silicon SciFi DIS - Madrid, April 2009

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