SU(3) breaking effects in hyperon semi-leptonic decays and the EMC/SLAC proton spin measurements

The problem of analysing hyperon semi-leptonic decay data is discussed with particular reference to SU(3) symmetry breaking effects and the resulting predictions for the spin structure of the proton. It turns out that the present decay data can be accommodated exceedingly well by a simple approach treating solely the so-called recoil effect or centre-of-mass correction. The extracted F and D parameters, of particular relevance to present discussions of the structure functions for polarized deep-inelastic scattering, are very stable and strikingly close to the results of earlier analyses. The implication is that the F and D thus extracted may reliably be used in predicting the flavour non-singlet contribution to the proton g1. This last being thus still in marked conflict with the EMC/SLAC results on polarized deep-inelastic scattering. (orig.)