Strange Quarks in the Nucleon

1. Strange Quarks in the Nucleon Strange Quark Parton Distributions from K± Production in DIS on the Deuteron H. E. Jackson Argonne National Laboratory for The HERMES Collaboration arXiv:0803.2993

2. ¹ ( ( ) ) ( ) ( ( ) ( ) ) = d 2 0 5 + ¹ ¹ ¹ ¼ º s x º s x r u x x r = = ( ) ( ) h ¢ S 0 0 8 5 0 0 1 3 0 0 0 8 t ¡ § § ; : e o e x p = : : : ( ) ( ) ( ) S + ¹ x s x s x = What do we know about S(x) and ΔS(x)? • Charm production in scattering is current source of information on . Extraction of pdfs is uncertain because of heavy quark mass effects in final state . • Usual Assumption is at some low factorization scale • Recent inclusive polarized DIS (e,e’) experiments with the deuteron give for the helicity distribution See Lai et al., JHEP0704, 89 (2007) HERMES, PRD75, 012007(2007) H. E. Jackson DIS 2008

3. Status of ΔS(x)(cont’d) • But recent results from semi-inclusive DIS at HERMES using flavor tagging of hadron spin asymmetries Ah1(x,Q2) suggest • ΔS(x)≈0 PRD71,(2005)012003 H. E. Jackson DIS 2008

4. D I S 2 ( ) d N ( ) ( ) ( ) S 2 x ( ) [ ( ) ( ) ] + ¹ K Q Q S 5 2 ´ + x s x s x x x x = U ¹ ( ) ( ) ( ) ( ) ( ) 2 d d Q d d Q ; + + + ¹ x ´ x u x u x x x Extraction of strange pdfs with isoscalar targets • Strange quarks carry no isospin → s(x)proton=s(x)neutron • In deuteron fragmentation in DIS can be described with fragmentation functions with no isospin dependence. • Require only isospin symmetry between the proton and neutron, and charge-conjugation invariance in fragmentation. • In LO the scattering cross sections can be written in terms of two pdfs, eg. • Where H. E. Jackson DIS 2008

5. K K R R ( ) ( ) ( ) d d S D D x z z z z Q S h i K 2 K 2 ( ) d N ( ) d N K K R R x ( ) ( ) ( ) ( ) K K 2 R R d d S D Q D x ( ) [ ( 5 ) ( ) ( ) ( ) ] ¡ d d K K K K K K Q Q D S D ( ) ( ) ( ) ( ) ( ) + ' x z z x z z d D D D D D 4 2 x x z z x z z + = U S Q ( ) ´ ´ d z z z a n z z N D I S Q S 2 d d Q ; x d Q S x u s Isoscalar targets(cont’d) Similarly, for semi-inclusive charged kaon production where Neglecting 2S(x) compared to 5Q(x) gives Providing access to if can be determined from the multiplicity. H. E. Jackson DIS 2008

6. Flavor tagging with Semi-inclusive DIS • Observation of a coincident hadron in DIS probes flavor in detail because of the correlation between the flavor structure of the exiting hadron and that of struck quark. • In the measurement reported here K± production on a deuteron target has been used to probe the strange sea. K± x=Q2/2m =E-E’ Q2=-q2=4EE’sin2( /2) zh=Ehadron/ H. E. Jackson DIS 2008

7. K K R R ( ) ( ) d & d D D z z z z Q S § K K R R K ( ) ( ) ( ) ( ) d d Q D S D + ( ) d N x z z x z z x Q S = D I S ( ) ( ) d Q S N 5 2 + x x K± multiplicities in d(e,e’)K±,x • Born multiplicities in 4π • S(x) from CTEQ6L with • as free parameters (dotted) does not fit data • In LO the charged kaon multiplicity is H. E. Jackson DIS 2008

8. 0 8 0 8 K R ( ) K R d D 0 3 9 8 0 0 1 0 : ( ) ( ) § d S D : z z à = K K x z z R R Q ( ) ( ) ( ) ( ) d d Q D S D K : : 0 2 + S R ( ) 0 2 K d x z z x z z D ( ) d N Q S : z z : x Q 0 2 > x ( ) ( ) ! Q S = 5 2 + x x D I S 5 d N : Fitting dNK(x)/dNDIS(x) Using this value and CTEQ6L values of Q(x) we have extracted in LO the product H. E. Jackson DIS 2008

9. 0 8 0 8 K R ( ) K R d D 0 3 9 8 0 0 1 0 : ( ) ( ) § d S D : z z à = K K x z z R R Q ( ) ( ) ( ) ( ) d d Q D S D K : : 0 2 + S R ( ) 0 2 K d x z z x z z D ( ) d N Q S : z z : x Q 0 2 > x ( ) ( ) ! Q S = 5 2 + x x D I S 5 d N : Fitting dNK(x)/dNDIS(x) Using this value and CTEQ6L values of Q(x) we have extracted in LO the product H. E. Jackson DIS 2008

10. 0 8 K R ( ) d D 1 2 7 0 1 3 : § z z = S : : 0 2 : S(x) at Q20=2.5 GeV2 • xS(x) obtained by evolution of data to 2.5 GeV2 by taking • Shape incompatable with CTEQ6L and with average of isoscalar nonstrange sea. D. de Florian, et al., PRD75, 114010 (2007) H. E. Jackson DIS 2008

11. K K R R [ ( ) ( ) ( ) ( ) ] d d ¢ Q D ¢ S D + x z z x z z K 2 D I S ( ) § d ( ) N Q S d N K 2 x 2 ( ) ( ) x ( ) ( ) [ ( ) ( ) ] A K Q A K Q ¢ Q ¢ S 5 2 £ + x x x x x x = L L = k L L d k 2 d d d Q 2 ; d d Q ; x x ; ; Extraction of ΔQ(x) and ΔS(x) Double-spin asymmetries for deuteron target H. E. Jackson DIS 2008

12. 2 2 Q G V 2 5 e = 0 : Helicity distributions at • 0.02<xBj<0.6 • q8=Q-2S • a8´ q8=s01 q8(x)dx =0.586§ 0.031 from hyperon decay and SU(3) symmetry H. E. Jackson DIS 2008

13. Summary and conclusions • Shape of S(x) is much softer than that of the light isoscalar sea. • SU(3) symmetry appears to be violated by strange quark pdfs. • Earlier conclusions from HERMES SIDIS of an unpolarized sea are confirmed. • Results for S(x) provide new information on the origins of the proton sea. • If s01 S(x)dx 0 (as indicated in inclusive experiments) some non-trival features of  S(x,Q2) at low x must emerge from experiment. H. E. Jackson DIS 2008

14. Additional figures H. E. Jackson DIS 2008

15. A1,d(x) vs A1,dK§(x) H. E. Jackson DIS 2008

16. 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 DIS 2008

17. The low energy issue • 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.) • If the axial form factor results can be extrapolated to zero they suggest that indeed  s < 0 . • 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 DIS 2008