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

2. 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; % polarization
E.C. Aschenauer

3. News on the spin structure of the nucleon
Naïve parton model
BUT
1989 EMC measured
S =
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

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

5. 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

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

7. 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

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

9. 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

10. 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

11. 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

12. 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±
1.41±
E.C. Aschenauer

13. 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

14. NLO FIT to DIS & SIDIS Data
D. De Florian et al. hep-ph/
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

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

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

17. 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

18. 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

19. 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

20. 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/
used for Dg/g extraction
Dg/g=0.016±0.058(stat.)±0.055(syst.)
m2=3.0GeV2
E.C. Aschenauer

21. 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

22. 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/
E.C. Aschenauer

23. Summary
talk by H. Avakian
E.C. Aschenauer

24. BACKUP SLIDES
E.C. Aschenauer

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

26. Purities
E.C. Aschenauer

27. Kaon Multiplicities
E.C. Aschenauer

28. AAC low x-extrpolation
E.C. Aschenauer

29. E.C. Aschenauer

30. E.C. Aschenauer

31. 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