1. --- New Results from HERMES ---
The Spin of the Nucleon
--- New Results from HERMES ---
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

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
DIS-06 - Tsukuba April 2006

3. 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
DIS-06 - Tsukuba April 2006

4. 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
DIS-06 - Tsukuba April 2006

5. NLO FIT to inclusive and semi-inclusive Data
D. De Florian et al. hep-ph/
Sidis-data improve description of all Dq’s; crucial for light sea
FF very crucial :
Kretzer favors SU(3) flavor symmetric sea; KKP broken one
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

6. 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
0.379±0.002±
1.722±0.024±
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

7. Results for DQ and DS Earlier HERMES conclusions of
unpolarised strange sea confirmed
factor 2 smaller error bars
Errors very sensitive to FF input
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

8. 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
DIS-06 - Tsukuba April 2006

9. 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)
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
DIS-06 - Tsukuba April 2006

10. Collins moments Collins moment: p+ > 0 p- < 0
[PRL94(2005),012002; hep-ex ]
p- unexpected large
role of unfavoured FF
first data for Collins FF
available from Belle
extraction of h1 from
Hermes asymmetries
K+ > K- > 0
K+ in agreement with p+
2005 data:
2 dimensional binning
disentangle x (PDF) and
z (FF) dependence
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

11. 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
DIS-06 - Tsukuba April 2006

12. Sivers moments sea quarks important Sivers moment: p+ > 0 p- ~ 0
[PRL94(2005),012002; hep-ex ]
Sivers moment:
p+ > p- ~ 0
K+ > K- ~ 0
K+ >= p+
sea quarks important
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
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

13. Study of hard exclusive processes leads to
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
DIS-06 - Tsukuba April 2006

14. GPDs Introduction AUT,sp+ AUT,sr,F,w AC,ALU, AUT, AUL
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
DIS-06 - Tsukuba April 2006

15. DVCS 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
DIS-06 - Tsukuba April 2006

16. DVCS-TTSA first model dependent extraction of Ju possible Code: VGG
Jd assumed to be zero
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

17. Can we constrain (Ju+Jd)
same statistics with electron beam on tape
independent data set to constrain (Ju+Jd)
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

18. 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
DIS-06 - Tsukuba April 2006

19. Summary and And much more to come
A lot of new results on the different components of the nucleon spin
polarized quark distributions
Transversity and Sivers
Exclusive reactions:
DVCS AUT (Ju+Jd)
excl. r production AUT Ju
And much more to come
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

20. The end of polarized targets at HERMES
DVCS exclusivity by missing mass Mx
Improve Exclusivity
Detect recoiling proton
modify target region
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

21. 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
Commissioning has started
Build by DESY, Erlangen, Ferrara, Frascati,
Gent, Giessen and Glasgow
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

22. Transversity: L. Pappalardo Tu. 16.30
Spin is fascinating
More from HERMES:
Transversity: L. Pappalardo Tu
DVCS: Z. Ye Fr
SDME: B. Marianski Fr
DS: M. Ehrenfried Sa
L(1520): S. Wang Sa
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

23. BACKUP SLIDES
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

24. Purities
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

25. Kaon Multiplicities
E.C. Aschenauer
DIS-06 - Tsukuba April 2006

26. VM-Contribution basically no VM contribution for Kaons E.C. Aschenauer
DIS-06 - Tsukuba April 2006