1. Spin Physics at Delia Hasch (for the HERMES collaboration)
17th international spin physics symposium
October 02-07, 2006; Kyoto (Japan)

2. the spin of the nucleon DS outline: prerequisites
final results on g1 for the proton and deuteron
flavour decomposition of Dq
talks by L.DeNardo, H.Jackson
new result on DG
talk by P. Liebing
news on transversity & friends
talks by M.Diefenthaler, M.Contalbrigo
hunting DL: DVCS, excl. r0
talks by W.D.Nowak, H.Guler, E. Kinney
new results on L polarisation (not covered) talk by K.Rith
Delia Hasch spin Physics at Hermes Kyoto (Japan),

3. Hermes @ DESY Stern-Gerlach separation 27.5 GeV (e+/e-)
resolution: dp/p~2%, dq<1 mrad
particle ID: lepton ID with e~98%, hadron contamination <1%
RICH: p, K, p ID within 2<Eh<15 GeV
self-polarised electrons: e
<Pb>~ 53±2.5 %
27.5 GeV (e+/e-)
<Pb>~ 53±2.5 %
Stern-Gerlach separation
kinematic range = 7 GeV:
0.2 < Q2 < 20 GeV2
0.004 < x < 0.9
for Q2 > 1 GeV2 : x > 0.02
1H→ <|Pt|> ~ 85 ±3.8 %
2H→ <|Pt|> ~ 84 ±3.5 %
1H <|Pt|> ~ 74 ±4.2 %
pure nuclear-polarised atomic gas, flipped at 90s time intervals
Delia Hasch spin Physics at Hermes Kyoto (Japan),

4. polarised structure function g1
Delia Hasch spin Physics at Hermes Kyoto (Japan),

5. polarised structure function g1x
[Q2>1 GeV2 data only]
see talk by L. DeNardo
assume saturation of G1d :
a0= DS (theory) (exp) (evol)
= ± ± ± 0.028 MS
Delia Hasch spin Physics at Hermes Kyoto (Japan),

6. Dq and DG from inclusive data
Duv and Ddv (quite) well determined:
Duv >0, Ddv <0
Dq and DG weakly constraint by data
Delia Hasch spin Physics at Hermes Kyoto (Japan),

7. how to further proceed ? OR:
unpolarised DIS
Dq and DG from inclusive DIS data via evolution equations :
requires wide kinematic
range in Q2 and x
only fixed target spin
experiments so far …
need polarised collider to
extend kinematic coverage
need more direct
probes
OR:
Delia Hasch spin Physics at Hermes Kyoto (Japan),

8. polarised semi-inclusive DIS
, z=Eh/n
probability that struck quark
of flavour f fragments into
hadron of type h with energy
fraction z
fragmentation
function
distribution
function
Delia Hasch spin Physics at Hermes Kyoto (Japan),

9. polarised semi-inclusive DIS
, z=Eh/n
probability that struck quark
of flavour f fragments into
hadron of type h with energy
fraction z
flavour tagging
p+ ud
K- us
p- ud
‘purities’
(based on MC tuned to
HERMES multiplicities)
Delia Hasch spin Physics at Hermes Kyoto (Japan),

10. quark/anti-quark helicity distributions
[HERMES, PRL92(2004), PRD71(2005)]
u quarks large positive polarisation
d quarks negative polarisation
sea quarks (u, d, s ,s) compatible with 0 : in measured x-range: ( ): - x
Delia Hasch spin Physics at Hermes Kyoto (Japan),

11. ‘isoscalar’ extraction DS
[HERMES, PRL92(2004), PRD71(2005)]
strange quarks carry no isospin (same in p, n)
deuterium is isoscalar target
 fragmentation simplifies
all needed information extracted from
HERMES data alone:
A1d(x,Q2) , A1K(x,Q2)
kaon multiplicities
assumptions:  isospin symmetry
 charge conjugation
Delia Hasch spin Physics at Hermes Kyoto (Japan),

12. ‘isoscalar’ extraction DS
[HERMES, PRL92(2004), PRD71(2005)]
strange quarks carry no isospin (same in p, n)
deuterium is isoscalar target
 fragmentation simplifies
all needed information extracted from
HERMES data alone:
A1d(x,Q2) , A1K(x,Q2)
kaon multiplicities
assumptions:  isospin symmetry
 charge conjugation x x
Delia Hasch spin Physics at Hermes Kyoto (Japan),

13. ‘isoscalar’ extraction DS
[HERMES, PRL92(2004), PRD71(2005)]
 earlier Ds result confirmed with factor 2 smaller errors:
xDS(x)/2
see talk by H. Jackson
Delia Hasch spin Physics at Hermes Kyoto (Japan), x

14. direct measurement of DG
golden channel: charm production
@HERMES: hadron production at high PT
hard scale is PT
method I:
method II:
MC: PYTHIA6.2
Bg-processes: DIS, QCDC, direct+resolved g
Delia Hasch spin Physics at Hermes Kyoto (Japan),

15. direct measurement of DGx
Dg/g
golden channel: charm production
@HERMES: hadron production at high PT :
hard scale is PT
method I:
method II:
see talk by P. Liebing
<m2>=1.35 GeV2
MC: PYTHIA6.2
Bg-processes: DIS, QCDC, direct+resolved g
+0.127
-0.105
(sys-model)
Delia Hasch spin Physics at Hermes Kyoto (Japan),

16. quark structure of the nucleon
Delia Hasch spin Physics at Hermes Kyoto (Japan),

17. quark structure of the nucleon
unpolarised quarks
and nucleons
longitudinally polarised quarks and nucleons
transversely polarised
quarks and nucleons
h1(x): helicity flip
chiral-odd  needs a
chiral odd partner:
SIDIS: COLLINS-FF 
azimuthal asymmetry AUT
Delia Hasch spin Physics at Hermes Kyoto (Japan),

18. HERMES transverse running
transversally polarised p (Pt = 0.78±0.04)
0.3T transverse holding field
2002: first results [PRL94(2005)]
preliminary data 
[hep-ex/ ]
Delia Hasch spin Physics at Hermes Kyoto (Japan),

19. asymmetries and moments
[angle and moments definitions according to Trento conventions]
Collins moment
Sivers moment
Collins and Sivers moments extracted by fitting the asymmetry with:
Delia Hasch spin Physics at Hermes Kyoto (Japan),

20. Collins asymmetries p+/-
significantly positive p+ and
negative p- asymmetries
unexpected large p-
role of unfavoured
fragmentation function?
measurement of
from
see talk by M. Diefenthaler
K+/-
Delia Hasch spin Physics at Hermes Kyoto (Japan),

21. what can we learn from Collins AUT?
[Efremov et al. hep-ph/ ]
h1 from cQSM
Collins FF:
x-dependence:
Hermes data fitted to
obtain parameters for
ansatz for CollinsFF
z-dependence:
BELLE data fitted and
asymmetry for Hermes
calculated
HERMES+BELLE
data in agreement 
Delia Hasch spin Physics at Hermes Kyoto (Japan),

22. Sivers asymmetries p+/-
significantly positive p+
asymmetry
requires non-zero orbital
angular momentum
first hint of naïve T-odd DF
from DIS
 test of universality:
K+/-
see talk by M. Diefenthaler
D1 known  Sivers DF
can be extracted from
HERMES data !
Delia Hasch spin Physics at Hermes Kyoto (Japan),

23. two-hadron asymmetry
interference arises from different partial waves of p+p- system
!collinear factorisation!  relativ. momentum: R=(Pp++Pp-)/2
can have transv. component even when integrating over PT of the pair
 needs new unknown 2hadron fragmentation function
[Jaffe etal,PRL80,1998]
[Radici etal,PRD65,2002]
Mpp
Mpp
Delia Hasch spin Physics at Hermes Kyoto (Japan),

24. two-hadron asymmetry see talk by M. Contalbrigo positive moments for
all invariant mass bins
0.040±0.009 (stat) ±0.003 (sys)
Delia Hasch spin Physics at Hermes Kyoto (Japan),

25. hunting for Lq    hard exclusive processes:
Generalised Parton Distributions Q2 t
Q2>>, t<<
Quantum number of final state selects different GPDs:
Vector mesons (r, w, f): H E
Pseudoscalar mesons (p, h): H E
DVCS (g) depends on H, E, H, E ~  
10-30%(DIS)
( H + E) x dx = Jq
= 1/2 DS + Lz
Delia Hasch spin Physics at Hermes Kyoto (Japan),

26. exclusivity @HERMES missing mass (energy) technique
e+/e-
27.5 GeV
Pb=55% MC
associated BH
Bethe-Heitler
+ data
(detected)
missing mass (energy)
technique
background estimated by MC
no recoil detection
Delia Hasch spin Physics at Hermes Kyoto (Japan),

27. Deeply Virtual Compton Scattering
Bethe-Heitler
DVCS
Bethe-Heitler
DVCS-BH interference leads to
non-zero azimuthal asymmetry
Delia Hasch spin Physics at Hermes Kyoto (Japan),

28. DVCS asymmetries DsUT I~Ds ~ DsC ~ cosf ∙Re{ H + xH +… }  ~
 different charges: e+ e-
DsC ~ cosf ∙Re{ H + xH +… } ~ H 
polarisation observables:
see talk by H. Guler
DsLU ~ sinf∙Im{H + xH + kE} ~
DsUT
beam target H
DsUL ~ sinf∙Im{H + xH + …} ~ ~  H
DsUT ~ sinf∙Im{k(H - E) + … }
H, E 
Delia Hasch spin Physics at Hermes Kyoto (Japan),
kinematically suppressed
x = xB/(2-xB ),k = t/4M2

29. DVCS: beam charge asymmetry
[hep-ex/ , subm.to PRL]
e+/- p → e+/- p g (MX<1.7 GeV)
(in HERMES acceptance)
Regge, D-term
Regge, no D-term
fac., D-term
fac., no D-term
GPD calculations:
different parametrisations for H
Vanderhaeghen (1999/02) –
 AC sensitive to GPD-models
tiny e-p sample (L=10pb-1)
HERA: 2005/06 e- beam (10x)
Delia Hasch spin Physics at Hermes Kyoto (Japan),

30. DVCS: longitudinal target-spin asymmetry
sinf in agreement with
GPD models
unexpected large sin2f
(twist-3)
Delia Hasch spin Physics at Hermes Kyoto (Japan),

31. DVCS: transverse target-spin asymmetry
[ data]
GPD model by:
[Goeke et al. (2001)]
[Ellinghaus et al. (2005)]
see talk by W.D. Nowak
first model dependent constrain on Ju+Jd
Delia Hasch spin Physics at Hermes Kyoto (Japan),

32. r0 transverse target-spin asymmetry
interference of H and E:
sS ~ |ST| sin (f-fS) E∙H
[curves: Vinnikov et al. (2005)]
GPD model calculations: quark+gluon GPDs
E related to Jq  TSA sensitive to Jq
see talk by E. Kinney
add 2005 data: sL/sT separation
(meson production: factorisation for longitudinal photons only)
Delia Hasch spin Physics at Hermes Kyoto (Japan),

33. summary: HERMES view at the nucleon structure
polarised DIS + HERMES:
from unpolarised
DIS
first glimpse
a0
=0.330±0.025(exp)
 signals of GPDs  Ju+Jd
transversity is
non-zero!
first T-odd DF in
DIS
direct
flavour
decomp.
new constrain on Ds
Delia Hasch spin Physics at Hermes Kyoto (Japan),

34. Backup slides

35. HERMES future June 2007 add 2005: p data transversity+friends
exclusive AUT (DVCS, r0, p0)
 :
e+/e-
27.5 GeV
dedicated measurements of hard
exclusive processes with recoil
Delia Hasch spin Physics at Hermes Kyoto (Japan),

36. contribution from exclusive VM in sidis sample
 basically no VM contribution for kaons

37. polarised gluon distribution
3 data samples:
‘anti-tagged’ : e+ not in acceptance
pT measured w.r.t. beamline
‘tagged’ : e+ identified
hadron pairs
 different bg contributions, different systematics
Dg/g

38. DVCS: TTSA constrain on Ju+Jd