The Helicity Structure of the Nucleon from Lepton Nucleon Scattering E.C. Aschenauer

The contemporary experiments Beam: ≤6 GeV e-; 85% polarization Target: polarized targets 3He, 6LiD, NH3 Beam: 27.5 GeV e±; <50>% polarization Target: (un)-polarized gas targets; <85%> polarization Beam: 160 GeV m; 75% polarization Target: 6LiD; 50% polarization E.C. Aschenauer

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

Deep Inelastic Scattering FF Important kinematic variables: q DF cross section: Spin 1 E.C. Aschenauer

How to measure Quark Polarizations Virtual photon g* can only couple to quarks of opposite helicity Select q+(x) or q-(x) by changing the orientation of target nucleon spin or helicity of incident lepton beam Asymmetry definition: inclusive DIS: only e’ info used semi-inclusive DIS: e’+h info used E.C. Aschenauer

World data on inclusive DIS Combine p and d to get n: or 3He What can we learn on the PDFs Compass: hep-ex/0609038 Hermes: hep-ex/0609039 E.C. Aschenauer

HERMES: Integrals Saturation in deuteron integral is assumed use only deuterium from hyperon beta decay (a8=0.586±0.031) From neutron beta decay a3=1.269±0.003 Q2=5 GeV2, NNLO in MS scheme E.C. Aschenauer

Compass: QCD-fit Input parameterizations: E.C. Aschenauer

JLAB: High x behaviour extract PDFs using world A1p Hall-A: CLAS: A1n from 3He extract PDFs using world A1p CLAS: Proton Deuterium E.C. Aschenauer

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

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

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 0.41±0.02 1.103 1.111 1.41±0.29 0.783 0.296 E.C. Aschenauer

Results for DQ and DS Earlier HERMES conclusions of unpolarized strange sea confirmed factor 2 smaller error bars Errors very sensitive to FF input E.C. Aschenauer

NLO FIT to DIS & SIDIS Data D. De Florian et al. hep-ph/0504155 NLO @ Q2=10 GeV2 Kretzer KKP c2DIS c2SIDIS Duv Du Ddv Dd Ds Dg DS 206 225 231 0.94 0.70 -0.26 -0.34 0.087 -0.049 -0.11 -0.055 -0.045 -0.051 0.57 0.68 0.31 0.28 SIDIS data improves description of all Dq, especially light sea Kretzer FF favor SU(3) symmetric sea, not so for KKP DS ~30% in all cases E.C. Aschenauer

Unpolarized Gluon Distribution big Q2-x lever arm very accurate G(x) E.C. Aschenauer

How to measure DG fixed target experiments small Q2-x lever arm even sign of DG unknown Indirect from scaling violation hep-ph/0603213 E.C. Aschenauer

The golden channels Idea: Direct measurement of DG Isolate the photon gluon fusion process (PGF) Open Charm production Reaction: LO-MC: Aroma E.C. Aschenauer

The golden channels Idea: Direct measurement of DG --- h±h± h± Isolate the photon gluon fusion process detection of hadronic final states with high pT high pT pairs of hadrons single high pT hadrons COMPASS HERMES h±h± --- h± less sub-processes contributing  more sub-processes contributing  higher statistics  h±h± vs. h±: h± more inclusive → pQCD NLO calculations (easier) possible E.C. Aschenauer

COMPASS Results Channel: h±h± with Q2>1GeV2 Cuts: LO-MC: LEPTO Considered sub-processes: LO-MC: LEPTO 10% of stat. Q2>1GeV2 0.33±0.07 Dg/g=0.06±0.31(stat.)±0.06(syst.) m2=2.3GeV2 E.C. Aschenauer

COMPASS Results Channel: h±h± with Q2<1GeV2 Cuts: LO-MC: PYTHIA 6.2 Considered sub-processes: LO-MC: PYTHIA 6.2 COMPASS standard values: hep-ph/0505157 used for Dg/g extraction Dg/g=0.016±0.058(stat.)±0.055(syst.) m2=3.0GeV2 E.C. Aschenauer

HERMES Results Channels: h± with Q2<0.1GeV2; pT>1GeV h±h± with Q2<0.1GeV2; h± with Q2>0.1GeV2; PT>1GeV h± with Q2<0.1GeV2; pT>1GeV Considered sub-processes: LO-MC: PYTHIA 6.2 E.C. Aschenauer

HERMES Results kT, pT standard values: Minimize the difference between HERMES cross section: kT, pT standard values: M.Anselmino et al. Phys. Rev. D71,074006 Minimize the difference between by fitting a function for Dg/g Dg/g results for different final states hep-ph/0505157 E.C. Aschenauer

Summary talk by H. Avakian E.C. Aschenauer

BACKUP SLIDES E.C. Aschenauer

Measured Asymmetries Deuterium Proton statistics sufficient for 5 parameter fit E.C. Aschenauer

Purities E.C. Aschenauer

Kaon Multiplicities E.C. Aschenauer

AAC low x-extrpolation E.C. Aschenauer

E.C. Aschenauer

E.C. Aschenauer

DG/G = 0.41±0.18±0.03 at x=0.17±0.11 and m2=2.1GeV2 Old analysis: pairs of high pT hadrons pTh1>1.5GeV and pTh2>0.8GeV MC used Pythia-5 only polarized proton data no determination of systematic uncertainty due to MC-model E.C. Aschenauer