1. On behalf of the HERMES collaboration
Measurement of S in the nucleon from semi-inclusive DIS on the Deuteron
On behalf of the HERMES collaboration
H. E. Jackson

2. Why the interest in  S?
But recent results from semi-inclusive DIS at HERMES using flavor tagging of hadron spin aysmmetries Ah1(x,Q2) suggest ΔS=0
PRD71,(2005)012003
H. E. Jackson, spin2006

3. 27 GeV e +/ e- beam of HERA ep collider
H. E. Jackson, spin2006

4. The HERMES Spectrometer
H. E. Jackson, spin2006

5. Spin-dependent deep-inelastic scattering(DIS)
Inclusive polarized DIS has provided much of our knowledge of partonic structure of the nucleon.
Semi-inclusive DIS, observation of a coincident hadron, allows probing of flavor in more detail because the flavor structure of the hadron and struck quark are correlated.
In the exp. reported here, K± double-spin asymmetries on a isoscalar deuteron target have been used to probe the strange quark sea. K±
x=Q2/2m  =E-E’
Q2=-q2=4EE’sin2( /2) zh=Ehadron/
H. E. Jackson, spin2006

6. “Isoscalar” extraction of S
H. E. Jackson, spin2006

7. Isoscalar extraction - formalism
H. E. Jackson, spin2006

8. Formalism – cont’d
H. E. Jackson, spin2006

9. Extraction of s D(z)dz ’s
H. E. Jackson, spin2006

10. Exp. inclusive and kaon spin asymmetries
Kaon asymm. is small and slightly positive
H. E. Jackson, spin2006

11. Quark polarizations and helicity distr’s
.02<xbj <1
H. E. Jackson, spin2006

12. (For the measured region, 0.02<xbj<1.0)
Conclusions
(For the measured region, 0.02<xbj<1.0)
∫ S(x)dx is 0 within error.
Data give direct measure of
a8 =  Q-2 S=0.274§ .039.
SU(3) value: a8 = 0.46.
SU(3) analysis of inclusive data not(?) valid.
∫ S(x)dx includes contribution from  G→small(≠1-2)
Earlier HERMES conclusions of unpolarized sea confirmed.
H. E. Jackson, spin2006

13. Other measurements
The value of the strange axial form factor at Q2=0 is equal to the integral of the strange quark helicity distribution at high Q2
GSa(Q2) has been extracted from combined analysis of PV measurements in elastic ep scattering (HAPPex and G0) and elastic p scattering (BNL E734)
Stephen Pate, et al., hep-ex/ v2
Q2 (GeV2)
H. E. Jackson, spin2006

14. The low energy issue
If the axial form factor results can be extrapolated to zero they suggest that indeed  s < 0 .
The DIS result that s is zero appears to contradict this result.
The discrepency could be resolved by the onset of large values of  s(x, Q2) at very low values of xbj , x ≈
Alternatively, a “x=0” contribution to the singlet axial charge coming from a non-perturbative gluon topological contribution has been proposed by Steve Bass, (RMP 77,(2005) 1257.)
Similarly, if SU(3) symmetry is preserved in hyperon decay, there must also be missing strength in q8(x) in the low x region.
H. E. Jackson, spin2006

15. Either earlier conclusions regarding s(x,Q2) are not correct OR
The message
Either earlier conclusions regarding s(x,Q2)
are not correct OR
Some non-trivial features of Δs(x,Q2) at low x
must emerge from experiment!
H. E. Jackson, spin2006