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Exploring Spin Structure Functions with Meson Cloud Model in Hadron Physics

This overview explores the Meson Cloud Model's crucial role in understanding spin structure functions of hadrons, focusing on contributions to g1 and g2, observed transverse effects, and insights from longitudinal and transverse spin components. Data from HERMES and other experiments inform the discussion, highlighting the model's implications for proton and neutron structure functions. Theoretical considerations, such as NLO evolution and hyperfine splitting, are also addressed.

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Exploring Spin Structure Functions with Meson Cloud Model in Hadron Physics

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  1. g1(x) and g2(x) in the Meson Cloud Model Tony Signal Institute of Fundamental Sciences Massey University New Zealand

  2. West Island

  3. Overview • Meson Cloud model • Meson cloud contributions to spin structure functions • Conclusion

  4. Meson Cloud Model • Crucial observation (Sullivan 72) - • Pion cloud contribution to DIS scales • Implies quark dists of proton modified • Convolution

  5. Meson Cloud Model

  6. Meson Cloud Model • Fock expansion of proton waveftn. • Bare states are SU(6) symmetric • p  BM vertices described by Lint plus form factor • FF constrained by elastic cross-sec • Quick convergence  Small prob. of high mass states • Model incorporates structure + interactions • Can investigate high-energy  low-energy pictures, symmetry breaking etc.

  7. Gottfried Sum Rule • Isospin broken in sea • MCM gives good fit to

  8. Spin dependent Quark Dists. • Extend MCM to include vector mesons • p cloud dilutes proton spin • r, w, K* able to carry spin • Include interference terms • Get reasonably good agreement with HERMES semi-inclusive data for sea distributions

  9. Spin Dependent Sea Dists. • Data from Hermes • Small symmetry breaking

  10. Spin Dependent Structure Functions • Dominated by valence distributions • NN, N most important fluctuations • At finite Q2 spin of cloud hadrons are not parallel with initial nucleon spin • Both longitudinal and transverse spin components of cloud contribute to observed structure functions

  11. Spin Dependent Structure Functions

  12. Spin Dependent Fluctuations • Long. Fluctuations require both N and D • s = 3/2 state important

  13. Spin Dependent Fluctuations • N is more important for transverse fluct. • n.b g  0.19

  14. ‘Bare’ Hadron SFs • Use bag model for N, D parton dists • Add Dg(x) ‘by hand’ • Hyperfine splitting between N and D • Use NLO evolution • Unpol. dists agree with DIS data • g2(x) from Wandzura-Wilczek • No higher twist component

  15. ‘Bare’ Hadron g1(x) • Data from Hermes

  16. ‘Bare’ Hadron g2(x) • Data from E155, Jlab E-99-117

  17. MCM Contributions to g1p

  18. MCM Contributions to g1n

  19. MCM Contributions to g2p

  20. MCM Contributions to g2n

  21. Summary • Longitudinal (g1) structure ftns of cloud hadrons affect observed transverse (g2) structure ftns • MCM contributions to g1 and g2 of proton are small • MCM contributions to g1, g2 of neutron are 10% • Similar size to higher twist in g2n • Theorists have to be careful!

  22. Thanks • Fu-Guang Cao (Massey) • François Bissey (Massey)

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