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Delia Hasch

Spinstruktur des Nukleons -elektromagnetische Sonden bei hohen Energien-. Delia Hasch. KHuK - Perspektivtagung, GSI, 25/26. Oktober 2007. the spin of the nucleon. outline:. prerequisites. polarisation of quarks:. polarisation of gluons: D G. hunting for the OAM L q,g. new

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Delia Hasch

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  1. Spinstruktur des Nukleons-elektromagnetische Sonden bei hohen Energien- Delia Hasch KHuK - Perspektivtagung, GSI, 25/26. Oktober 2007

  2. the spin of the nucleon outline: • prerequisites • polarisation of quarks: • polarisation of gluons: DG • hunting for the OAM Lq,g new developments • transverse spin phenomena: transversity&friends

  3. how to study the nucleon structure ? … deep-inelastic scattering (DIS) : Q2 q factorisation: universal, parametrises the structure of the nucleon

  4. HERMES: 27 GeV e+, e- HERMES: p , d, 3He unpol. H, D, 4He, N, Ne, Kr, Xe Compass: d , p experimental prerequisites -the 2nd generation- 1995-2007 @DESY COMPASS @CERN: 160 GeV m+ 2002-2010-? f=1 f: target dilution factor f=1 gas targets, f~0.02 solid targets

  5. HERMES: 27 GeV e+, e- HERMES: p , d unpol. H, D, 4He, 14N, 20Ne, Kr, Xe Compass: d , p experimental prerequisites -the 2nd generation- hadron ID: COMPASS: 160 GeV m+ f=1

  6. HERMES: 27 GeV e+, e- SMC E155 HERMES E142 HERMES: p , d unpol. H, D, 4He, 14N, 20Ne, Kr, Xe Compass: d , p experimental prerequisites -the 2nd generation- hadron ID COMPASS: 160 GeV m+ f=1 DIS

  7. polarised structure function g1

  8. polarised structure function g1

  9. (exp) (theory) (evol) = 0.330 ± 0.025 ± 0.011 ± 0.028 a0=DS MS MS MS a0= DS = 0.35 ± 0.03(stat) ± 0.05(sys+evol) polarisation of quarks assume saturation of G1d : a0=DS from theory from hyperon beta decay QCD-fit:

  10. valence quarks are well determined: • Duv >0,Ddv <0 • gluons and sea quarks are poorly constraint by data Dq andDGfrom inclusive data SU(3)f symmetry implicitly assumed

  11. flavour separation: semi-inclusive DIS HERMES: only direct 5-flavour separation of polarised pdfs up in short: down • Du(x) is large and positive • Dd(x) is smaller and negative • Du, Dd, Ds are approx. zero ! u d awaiting results from  lower values of x strange Ds=0

  12. AAC GRSV BB LSS how to measure the gluon polarisation DG …reminder: from scaling violation [hep-ph/0603213]

  13. unpolarised DIS AAC GRSV BB LSS • need more direct probes how to measure the gluon polarisation DG …reminder: from scaling violation [hep-ph/0603213]

  14. direct measurement of DG • golden channel: charm production •  theoretically very clean •  experimentally very challenging Photon-Gluon Fusion (PGF) • hadron production at high PT(hard scale) • experimentally very clean  highly model dependent due to variety of background processes

  15. other sub-processes make life hard: q q qg + + + .. g g ‘direct’ measurement of DG • hadron production at high PT (hard scale) • experimentally very clean  highly model dependent PGF extraction relies on Monte Carlo description of subprocesses (pythia)

  16. direct measurement of DG • golden channel: charm production • hadron production at high PT HERMES Preliminary Dg/g @x[0.06,0.3] Dg/g ~ zero! x

  17. Q2 t hunting for Lq ≈30% ≈zero Ji’s sum rule: Generalised PartonDistributions(GPDs)appear in the factorisation scheme for hard exclusive processes

  18. generalised parton distributions longitudinal momentum fraction x at transverse location b T 3D picture of the nucleon GPDs only known framework to gain information on 3D picture of hadrons parton distributions longitudinal momentum fraction x form factors location of partons in nucleon • high beam energy (hard process) • very high luminosity (small cross sections) • complete event reconstruction (ensure exclusivity) very ambitious measurements

  19. Deeply Virtual Compton Scattering only @HERA • different beam charges • polarised beams • polarised targets DVCS transverse target-spin asymmetry: • sensitive to Jq Ju=0 Ju=0.2 Ju=0.4 GPD model by: [Goeke et al. (2001), code:VGG] [Ellinghaus et al. (2005)]

  20. hunting for Lq model dependent constraint of Ju vs Jd 0709.0450[nucl-ex] Ju+Jd/2.9=0.42±0.21(exp)±0.06(th) arXiv:0705.4295[hep-lat] dedicated measurements of exclusive processes: @HERMES with recoil detector (2006/07) JLab Hall-A and Hall-B experiments (2007++) hep-ex/0606061

  21. transverse spin phenomena [courtesy of A. Bacchetta, DESY] beyond collinear approximation

  22. the nucleon quark structure transversely polarised quarks and nucleons dq(x): helicity flip transversity longitudinally polarised quarks and nucleons Dq(x): helicity difference unpolarised quarks and nucleons q(x) spin averaged well known

  23. Peculiarities ofdq • probes relativistic nature of quarks • otherwise dq =Dq • no gluon analog for spin-1/2 nucleon • different Q2 evolution than Dq • sensitive to valence quark polarisation • only known way to obtain tensor charge the nucleon quark structure transversely polarised quarks and nucleons dq(x): helicity flip transversity longitudinally polarised quarks and nucleons Dq(x): helicity difference unpolarised quarks and nucleons q(x) spin averaged well known

  24. peculiarity of transversity DIS: hadron production: + - Chiral-oddfragmenation funtionCollinsFF : + - + - • transversity flips helicity of both quark and nucleon + ? - needs chiral-odd + golden channel + - - + - + - chiral-odd partner + - (PAX@FAIR) Drell-Yan:

  25. h q q h Collins fragmentation function CollinsFF H1(z,kT2)correlates transverse spin of fragmenting quark and transverse momentumPh of produced hadronh chiral–odd& naïve T–odd produces left-right asymmetry in the direction of the outgoinghadron  leads to single-spin asymmetries

  26. single-spin asymmetries Unpolarised lepton beam (U)  Transversely polarised target (T) distinct signature! Sivers distribution function: • describes correlation between intrinsic quark pT and transverse nucleon spin • non-zero Sivers DF requires non-vanishing orbital angular momentum • Chiral – even & naïve T – odd

  27. ep  pX crucial test of pQCD: Sivers asymmetries p+are substantial and positive: • first unambiguous evidence for a non-zeroT-odd distribution function in DIS • requires non-zero quark orbital angular momentum !

  28. ep  pX Collins asymmetries first time: transversity & Collins FF are non-zero! • p+ asymmetries positive – no surprise: u-quark dominance and expect dq>0 since Dq>0 • large negative p- asymmetries – ARE a surprise: suggests the disfavoured CollinsFF being large and with oposite sign:

  29. ep  pX Collins asymmetries • deuteron target:

  30. xdu(x) xdd(x) first glimpse of transversity [Anselmino et al. PRD75(2007)] up global fit down milestone!

  31. new concepts: GPDs  3D picture of the nucleon TMDs  beyond collinear approximation structure of the nucleon from polarised DIS : from unpolarised DIS first glimpse a0=DS =0.330±0.025(exp)  first signals of GPDs: Ju +Jd first extraction of dq direct flavour decomposition

  32. structure of the nucleon -the open tasks-  detailed measurement of x-dependence first glimpse  first signals of GPDs: Ju +Jd  detailed measurement in 3 kine variables first extraction of dq  extrapolation x0, x1  detailed measurement in 2 kine variables

  33. EIC, PAX@FAIR RHIC, EIC, (JPARC) polarised collider: EIC structure of the nucleon -the future facilities- first glimpse  first signals of GPDs: Ju +Jd first extraction of dq JLab@12GeV Compass-DVCS EIC

  34. e p future facilities high CM energies  wide kinematic range in x and Q2 high luminosities  mapping out observables differential in 2D and 3D polarised beams and targets @12 GeV  mapping out GPDs by measuring exclusive process Luminosity(*1030/cm2/s) 109 JLab@12GeV 108 107 JLab EIC (eRHIC, ELIC) 106 ELIC 105 107 104 • ‘dream machine’ for polarised DIS`: would address all open questions eRHIC 103 102 HERA HERMES 10 COMPASS 100 CM energy (GeV) 10 1

  35. future facilities high CM energies  wide kinematic range in x and Q2 high luminosities  mapping out observables differential in 2D and 3D polarised beams and targets EIC (eRHIC) Luminosity(*1030/cm2/s) 109 JLab@12GeV 108 107 JLab 106 ELIC 105 107 104 eRHIC 103 102 HERA HERMES 10 COMPASS 100 CM energy (GeV) 10 1

  36. Zusammenfassung neue Entwicklungen in der Spinphysik: ≈Null ≈30% Wege zur Messung aller Komponenten der Spin-SR sind aufgezeichnet; wir müssen sie gehen !  neue Anlagen (EIC) neue, komplementäre Konzepte/Entwicklungen: GPDs : Korrelation von longitudinalem Impuls + transvesaler Position  3D Abbild des Nukleons TMDs : Korrelation von transversalem Impuls + Spin  jenseits kollinearer Näherung

  37. Backup slides

  38. template -GPDs correlation of longitudinal momentum and transverse location • -TMDs correlation of transverse momentum and spin • explore spin-orbit structure • beyond collinear approximation • EIC: Lumi: • eRHIC: ~2*1032 /cm2/s • (~1033 /cm2/s with R&D) • ELIC: ~1034 /cm2/s

  39. polarised inclusive DIS spin1: often neglected… but:

  40. polarised structure function g1

  41. distribution function fragmentation function ‘purities’ (based on MC tuned to HERMES multiplicities) polarised semi -inclusive DIS

  42. unpolarised DIS • need more direct probes how to further proceed ? • Dq and DG from inclusive DIS data via evolution equations : • requires wide kinematic range in Q2 and x • only fixed targetspin experiments so far … need polarisedcollider to extend kinematic coverage OR:

  43. direct measurement of DG • golden channel: charm production •  theoretically very clean •  experimentally very challenging • @HERMES (√s=7 GeV): • hadron production at high PT ALL PythiaMC: Dg/g = -1 Dg/g = 0 Dg/g = +1

  44. direct measurement of DG • golden channel: charm production • @HERMES: hadron production at high PT : direct, resolved, soft processes [Pythia MC] signal processes: PGF QCD 22(g)

  45. direct measurement of DG • golden channel: charm production • @HERMES: hadron production at high PT

  46. CLAS MC Bethe-Heitler associated BH + data hunting for Lq Generalised Parton Distributions (GPDs) hard exclusive processes are difficult to measure: • high beam energy (hard process) • very high luminosity (small cross sections) • complete event reconstruction (ensure exclusivity) • no complete event reconstruction  missing mass (MX) technique: HERMES MN

  47. DVCS-BH interference leads to non-zero azimuthal asymmetry Deeply Virtual Compton Scattering Bethe-Heitler DVCS Bethe-Heitler

  48. ~ DsC~cosf∙Re{ H+ xH +… } ~ DsLU~sinf∙Im{H+ xH+ kE} DsUT polarisation observables: ~ DsUL~sinf∙Im{H+ xH+ …} beam target DVCS asymmetries I~Ds  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

  49. e+/- p→ e+/- p g (MX<1.7 GeV) (in HERMES acceptance) Regge, D-term Regge, no D-term fac., D-term fac., no D-term DVCS: beam charge asymmetry GPD calculations: different parametrisations forH • Vanderhaeghen(1999/02)–  AC sensitive to GPD-models tiny e-p sample (L=10pb-1) simultanous fit of charge and polarisation observables provide pure interference term HERA: 2005/06 e- beam (10x)

  50. Bg ~1% Bg ~10% prospects for exclusive processes  2006-07: e+/e- 27.5 GeV detection of recoiling proton dedicated measurements of hard exclusive processes with recoil

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