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Nucleon spin structure results (from the HERMES experiment)

Nucleon spin structure results (from the HERMES experiment). Michael Düren Universität Gießen. — XII Conference on Hadron Spectroscopy, Frascati, Oct. 10, 2007 —. a 0 = DS (theory) (exp) (evol) = 0.330 ± 0.011 ± 0.025 ± 0.028. MS.

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Nucleon spin structure results (from the HERMES experiment)

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  1. Nucleon spin structure results(from the HERMES experiment) Michael Düren Universität Gießen —XII Conference on Hadron Spectroscopy, Frascati, Oct. 10, 2007 —

  2. a0= DS(theory) (exp) (evol) = 0.330 ± 0.011 ± 0.025 ± 0.028 MS EMC 1988: Only 12±17% spin of the proton is explained by the spin of the up- and down- quarks Helicity sum rule: Remember: 1/3 of the proton spin comes the from quark spin

  3. The Experiment:* 1995 2007 *) proposed in ~1988 to solve the spin crisis ) plenty of beautiful data are waiting for being analyzed

  4. Novel techniques: longitudinally polarized high energy electron/positron beam at HERA for beam-spin and beam-charge asymmetries HERA electron beam27.5 GeV (e+/e-) <Pb>~ 53±2.5 % M. Düren, Univ. Giessen

  5. Novel techniques: The longitudinally and transverse polarized internal gas target for double spin asymmetries Storage cell target:high polarization, no dilution 1H→ <|Pt|> ~ 85 % 2H→ <|Pt|> ~ 84 % 1H <|Pt|> ~ 74 % M. Düren, Univ. Giessen

  6. Novel techniques: Dual radiator RICH for strangeness THE HERMES SPECTROMETER • resolution: • dp/p~2%, dq<1 mrad • PID: leptons with • e~98%, contam. <1% • hadronsp, K,p 2<Eh<15 GeV M. Düren, Univ. Giessen

  7. Novel techniques: Recoil detector for exclusive physics Silicon Detector ● Inside beam vacuum ● 16 double-sided sensors ● Momentum reconstruction & PID Scintillating Fiber Detector ● 2 barrels ● 2x2 parallel and 2x2 stereo layers ● 10° stereo angle ● Momentum reconstruction & PID 1 Tesla superconducting solenoid Photon Detector ● 3 layers of tungsten/scintillator ● PID for higher momenta ● detects M. Düren, Univ. Giessen

  8. Spin physics Hot topics in spin physics: • Moments and QCD-fits of PDFs • Strange sea polarisation; SU(3)f • Gluon spin • Transverse spin effects (do not appear in the helicity sum rule) • Orbital angular momentum of quarks; „3-D views“ of the proton; GPDs M. Düren, Univ. Giessen

  9. Polarized structure function g1p,d(x) proton deuteron M. Düren, Univ. Giessen HERMES data set most precise and complete in valence/sea overlap region [PRD 75 (2007)]

  10. First moment 1d [Q2>1 GeV2 data only] deuteron x a8 from hyperon beta decay MS DS = theory theory ωD=0.05±0.05 Deuteron data alone give  ! deuteron M. Düren, Univ. Giessen

  11. First moment 1d and  [Q2>1 GeV2 data only] deuteron x a8 from hyperon beta decay a0= DS(theory) (exp) (evol) = 0.330 ± 0.011 ± 0.025 ± 0.028 MS MS DS = theory theory ωD=0.05±0.05 Deuteron data alone give  ! Most precise result;Consistent with other experiments M. Düren, Univ. Giessen

  12. Valence quarks are well determined: • Duv>0,Ddv <0 q and G from inclusive data • Gluons and sea quarks are weakly constrained by data SU(3)f flavor symmetry implicitly assumed! M. Düren, Univ. Giessen

  13. Important remark on SU(3)fand the polarization of strange quarks • The violation of the Ellis-Jaffe sum rule means: • either the strange quark polarization Ds is negative • or SU(3)f flavor symmetry is broken • or low-x region different than assumed in parameterizations • Most analyses assume explicitly or implicitly SU(3)f flavor symmetry (e.g. in parameterizations of the PDFs) • Only semi-inclusive data can measure directly Ds Kaon asymmetries on deuteriumallow for the most directdetermination of Ds !Final analysis isin progress. M. Düren, Univ. Giessen

  14. Results (in short): u(x) is large and positive d(x) is smaller and negative s(x) is approx. zero Flavor separation from semi-inclusive data up HERMES: Only direct 5-flavor separation of polarized PDFs down u d [PRL92(2004), PRD71(2005)] strange M. Düren, Univ. Giessen

  15. Principles: Helicity conservation in polarized DIS: select specific quark spin orientation Hadron tagging: select specific quark flavor Matrix inversion brings you back from hadron asymmetries to quark spin flavor distributions Dqf (purity formalism) How does spin flavor separation qf(x) work? Keep beam spin constantand flip proton spin M. Düren, Univ. Giessen

  16. However, other sub-processes make life hard: q q qg + + + .. g g How does a direct gluon spin extraction work? Principle: • Large pT hadron pairs come from photon gluon fusion processes • They carry information of the gluon spin M. Düren, Univ. Giessen

  17. Measurement of gluon polarisation • HERMES: first measurement of gluon polarisation • [PRL 84 (2000)] TOPCITE 50+ • Further analysis going on: • Measurement of high pT pairs • Separation of the subprocesses • Two different methods • Significant reduction of Dg uncertainty • Still sign ambiguity at low x +0.127 Dg/g=0.071 ±0.034 ±0.010 For more details see talkby Riccardo FABBRI -0.105 M. Düren, Univ. Giessen

  18. Interesting properties of transversity: QCD-evolution independent of gluon distribution (to be tested by experiment) 1st moment of dq is tensor charge (pure valence object); value predicted by lattice QCD Quark density Helicity distribution Transversity Trans- versity Transverse spin effects There are two three leading-twist structure functions: M. Düren, Univ. Giessen • Transversity is chiral odd (i.e.does not contribute to inclusive DIS cross section!)

  19. Transverse spin distribution of quarks • The azimuthal angular distributions of hadrons from a transversely polarized target show two effects: • Collins asymmetry in sin(+s) • Sivers asymmetry in sin(-s) Target spin M. Düren, Univ. Giessen

  20. Transverse spin distribution of quarks • The azimuthal angular distributions of hadrons from a transversely polarized target show two effects: • Collins asymmetry in sin(+s)Product of the chiral-odd transversity distribution h1(x)and the chiral-odd fragmentation function H1(z) related to the transverse spin distribution of quarks • Sivers asymmetry in sin(-s) First results from Belle Target spin M. Düren, Univ. Giessen

  21. Transverse spin distribution of quarks • The azimuthal angular distributions of hadrons from a transversely polarized target show two effects: • Collins asymmetry in sin(+s)Product of the chiral-odd transversity distribution h1(x)and the chiral-odd fragmentation function H1(z) related to the transverse spin distribution of quarks • Sivers-Asymmetrie in sin(-s)Product of the T-odd distribution function f1T(x)and the ordinary fragmentation function D1(z) related to the orbital angular momentum of quarks First results from Belle Target spin M. Düren, Univ. Giessen

  22. attractive finalstate interaction photon photon  many goright Proton with spin out of this plane right left some goleft  photon photon Right-left symmetric Right-left SSA Sivers function is related to orbital angular momentum of quarks quarks Side view proton M. Düren, Univ. Giessen (M. Burkardt)

  23. First measurement of naïve T-odd distr. fkt. in DIS • Significant non zero asymmetries • Ap+>0, Ap-<0 • Evidence of SSA for pions [PRL94(2005)] Collins Sivers M. Düren, Univ. Giessen

  24. SSA for pions and kaons Collins Sivers Asiv(K+) > Asiv(p+) Sea quarks may provide important contribution to Sivers function For more details see talkby Luciano PAPPALARDO M. Düren, Univ. Giessen

  25. A Wigner operator can be defined that describes quarks in the nucleon; The reduced Wigner distribution is related toGPDs GPDs contain a more complete infothan form factors or parton distributions GPD General Parton DistributionsQuantum phase-space „tomography“ of the nucleon • Wigner introduced the first phase-space distribution in quantum mechanics (1932) The Wigner function contains the most complete (one-body) infoabout a quantum system. M. Düren, Univ. Giessen

  26. Quarks in quantum mechanical phase-space • Elastic form factors charge distribution (space coordinates) • Parton distributions momentum distribution of quark (momentum space) • Generalized parton distributions (GPDs) are reduced Wigner functions correlation in phase-space  e.g. the orbital momentum of quarks: • Angular momentum of quarks can be extracted from GPDs: Ji sum rule: • GPDs provide a unified theoretical framework for many experimental processes M. Düren, Univ. Giessen

  27. M. Düren, Univ. Giessen

  28. Q2 t Quantum number of final state selects different GPDs: Vector mesons (r, w, f): H E Pseudoscalar mesons (p, h): H E DVCS (g) depends on H, E, H, E ~ ~ ~ ~ Exclusive processes: The handbag diagram Q2large,t small • high Q2  hard regime • high luminosity  s~1/Q4, 1/Q6 • high resolution  exclusivity polarization provides new observables sensitive to different (combinations of) GPDs

  29. Beam Charge Asymmetry [PRD 75 (2007)] Deeply Virtual Compton Scattering (DVCS) only at HERA Beam Spin Asymmetry [PRL87(2001)] +100 top cite M. Düren, Univ. Giessen

  30. Hard exclusive meson productione p  e’ n p+ [hep-ex/0405078, arXiv 07070222 PLB submitted] • GPDs predictions: • Vanderhaeghen, Guichon & • Guidal [PRD 60 (1999)] • (LO and LO+ power corrections) • Model calculation: • Regge formalism, Laget • [PRD 70 (2004)] • LO predictions + power correction to space like pion form factor • in agreement with magnitude of data • Regge formalism for long. and transv. part of the cross section • provides good description of dependence of data Information on pion form factor at high Q2 and on polarised GPDs M. Düren, Univ. Giessen

  31. Quark total angular momentum AUT most sensitive observable to access Jq via GPDs • HERMES data 2002-04: • U: unpolarized beam • T: transv. pol. Target • ~50% of total stat. 0709.0450[nucl-ex] arXiv:0705.4295[hep-lat] GPD model by: [Goeke et al. (2001)] [Ellinghaus et al. (2005)] hep-ex/0606061 • first model dependent extraction of Ju &Jd possible • VGG-Code: GPD-model: LO/Regge/D-term=0 M. Düren, Univ. Giessen

  32. The HERMES recoil detector (2006-07) • Installed Dec 05, commissioned and successfully operated • Dedicated to exclusive processes: • Recoil proton detection • High luminosity: semi-incl. 2006: 7 M DIS events e- 20 M DIS events e+ 2007: 20 M DIS events e+ exclusive PID (first data) missing mass(from MC) For more details see talkby Tibor KERI M. Düren, Univ. Giessen

  33. Good bye Conclusions • 1/3 of the proton spin comes from quark spin • Direct measurements of the strange quark sea could not verify a negative strange polarization. This indicates a SU(3)f flavor symmetry breaking or large contributions from low x. • Analysis of gluon spin from inclusive DIS is difficult and ongoing • Transversity and Sivers functions are non-zero. Sivers asymmetry for kaon data indicates an orbital angular momentum contribution from sea quarks. • DVCS beam charge and beam spin asymmetrieshave been measured. First data of orbital angular momentum (OAM) fits to GPD functions indicate non-zero OAM of up-quarks • HERMES has the potential of further discoveries in spin physics with the new abundant recoil data! M. Düren, Univ. Giessen

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