The Spin of the Nucleon --- The View from HERMES --- E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

News on the spin structure of the nucleon Naïve parton model BUT 1989 EMC measured S = 0.120 0.094 0.138 ± Spin Puzzle Unpolarised structure fct. Gluons are important ! Sea quarks Dqs DG Full description of Jq and Jg needs orbital angular momentum E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

The quark content of the nucleon E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 World data on xg1(x,Q2) HERMES: very precise proton data most precise deuteron data most precise neutron data In measured range 0.004 < x < 0.9 at 2.5GeV2 Proton: a0 = 0.334± 0.101±0.007±0.002±0.014 Deuterium: a0 = 0.413± 0.056±0.007±0.009±0.005 with: E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

The structure function b1(x,Q2) Tensor structure function: E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

The structure function b1(x,Q2) First measurement of Azzd and b1 Azzd ¹ 0 Azzd ~ 1% b1 > 0 at small x in measured range 0.002-0.85: Qualitative agreement with coherent double scattering models E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Polarised quark distributions Correlation between detected hadron and struck qf “Flavor – Separation” Inclusive DIS: Semi-inclusive DIS: In LO-QCD: MC Extract Dq by solving: E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Polarized Quark Densities First complete separation of pol. PDFs without assumption on sea polarization Du(x) > 0 Dd(x) < 0 Polarised opposite to proton spin Polarised parallel to proton spin good agreement with NLO-QCD Du(x), Dd(x) ~ 0 No indication for Ds(x) < 0 In measured range (0.023 – 0.6) E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 Results for DQ and DS Inclusive Asymmetry Kaon Asymmetry Need a longitudinal polarized deuterium target strange quark sea in proton and neutron identical fragmentation simplifies All needed information can be extracted from HERMES data alone inclusive A1,d(x,Q2)and kaon AK1,d (x,Q2) double spin asym. Kaon multiplicities Only assumptions used: isospin symmetry between proton and neutron charge-conjugation invariance in fragmentation Fit x-dependence of multiplicities using PDFs from CTEQ-6 This Work Kretzer KKP 1.20±0.06±0.03 1.103 1.111 1.43±0.36±0.15 0.392 0.150 E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 Results for DQ and DS Direct measurement of a8 = DQ – 2DS = 0.274 ± 0.039 (0.02<x<1) SU(3) value: a8 = 0.586 ± 0.031 CNS included: a8 = 0.483 ± 0.026 Earlier HERMES conclusions of unpolarised strange sea confirmed factor 2 smaller error bars E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

The 3rd Twist-2 structure function unpolarised quarks and nucleons q(x): spin averaged vector charge well known longitudinally polarized quarks and nucleons Dq(x): helicity difference  axial charge known transversely polarized quarks and nucleons dq(x): helicity flip  tensor charge measuring! E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Peculiarities of transversity relativistic nature of quark: in absence of relativistic effects h1(x)=g1(x) Q2 –evolution: unlike for g1p(x), the gluon doesn’t mix with quark inh1p(x) (no gluon analog for spin-½ nucleon) sensitive to the valence quark polarisation q and q have opposite sign. _ tensor charge: first moment of h1 (large from lattice QCD) angular momentum sum rule for transversity chiral odd FF CHIRAL ODD NOT ALLOWED IN E.M. INTERACTIONS transversely polarized quarks and nucleons dq(x): helicity flip  tensor charge measuring ! double helicity flip single helicity flip E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 Collins moments [PRL94(2005),012002; hep-ex0507013] Collins moment: p+ > 0 p- < 0 p- unexpected large role of unfavoured FF first data for Collins FF available from Belle extraction of h1 from Hermes asymmetries 2005 data: 2 dimensional binning disentangle x (PDF) and z (FF) dependence Soon results for Kaons & p0 E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 SSA with two hadrons Another way to access h1 two hadrons in final state complementary process but new unknown fragmentation function Hydrogen target clear sin(FR^+FS) signal positive signal for all mass bins E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Azimuthal angles and asymmetries angle of hadron relative to final quark spin (Collins) (Collins) angle of hadron relative to initial quark spin (Sivers) (Sivers) chiral-even naïve T-odd DF related to parton orbital momentum violates naïve universality of PDF peculiarity of f^1T different sign of f^1T in DY E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 Sivers moments [PRL94(2005),012002; hep-ex0507013] Sivers moment: p+ > 0 p- ~ 0 non-zero orbital angular momentum in p-wave fct. Lq ?? opposite sign f1T^ in DIS and Drell-Yan 2005 data: FF known, extraction of Sivers function Soon results for Kaons & p0 E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

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 from DIS: HERMES ~0.3 exclusive: all products of the reaction are detected missing energy (DE) and missing Mass (Mx) = 0 E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 GPDs Introduction What does GPDs charaterize? unpolarized polarized conserve nucleon helicity flip nucleon helicity not accessible in DIS DVCS quantum numbers of final state select different GPD pseudo-scaler mesons vector mesons AC,ALU, AUT, AUL AUT,sp+ AUT,sr,F,w E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 DVCS two experimentally undistinguishable processes: HERMES kinematics: BH c.s. >> DVCS c.s. DVCS Bethe-Heitler (BH) p + D isolate BH-DVCS interference term non-zero azimuthal asymmetries transverse target spin asymmetry: E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 DVCS-TTSA first model dependent extraction of Ju possible factor 2 more data on tape E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 AUT - Exclusive r exclusivity ensured by DE background estimated by MC reconstruct r0 from h+h- Transverse Target Spin Asymmetry: 2005: factor 2 more statistics sL – sT separation AUT(F-Fs) sensitive to GPD E sensitivity to Ju E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

Workshop on Hadron Structure at JPARC - KEK DEC. 2005 Summary and A lot of new results on the different components of the nucleon spin polarized quark distributions: from inclusive and semi-inclusive measurements Transversity from single and two hadron production Sivers function Exclusive reactions: DVCS AUT---> Ju excl. r production AUT ---> Ju And much more to come E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

The end of polarized targets at HERMES DVCS exclusivity by missing mass Mx Improve Exclusivity Detect recoiling proton modify target region Detector to measure recoiling proton E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005

The HERMES Recoil Detector detection of the recoiling proton P: 135 – 1200 MeV/c 76% f acceptance p/p PID via dE/dx background suppression semi-incl.: 5 %® << 1% associated: 11% ® ~1% improved t-resolution study kinematical dependences data taking 2006/2007 Build by DESY, Erlangen, Ferrara, Frascati, Gent, Giessen and Glasgow E.C. Aschenauer Workshop on Hadron Structure at JPARC - KEK DEC. 2005