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

2. 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
Workshop on Hadron Structure at JPARC - KEK DEC. 2005

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

4. 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 < 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

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

6. 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 :
Qualitative agreement with
coherent double scattering
models
E.C. Aschenauer
Workshop on Hadron Structure at JPARC - KEK DEC. 2005

7. 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

8. 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

9. 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±
1.43±0.36±
E.C. Aschenauer
Workshop on Hadron Structure at JPARC - KEK DEC. 2005

10. Workshop on Hadron Structure at JPARC - KEK DEC. 2005
Results for DQ and DS
Direct measurement of
a8 = DQ – 2DS = ± (0.02<x<1)
SU(3) value: a8 = ± 0.031
CNS included: a8 = ± 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

11. 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

12. 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

13. Workshop on Hadron Structure at JPARC - KEK DEC. 2005
Collins moments
[PRL94(2005),012002; hep-ex ]
Collins moment:
p+ > 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

14. 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

15. 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

16. Workshop on Hadron Structure at JPARC - KEK DEC. 2005
Sivers moments
[PRL94(2005),012002; hep-ex ]
Sivers moment:
p+ > 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

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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