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

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

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

The HERMES Spectrometer H. E. Jackson, spin2006

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

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

Isoscalar extraction - formalism H. E. Jackson, spin2006

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

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

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

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

(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

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/0512032v2 0 Q2 (GeV2) 1.0 H. E. Jackson, spin2006

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 ≈ 10-2 - 10-3. 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

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