A Study of Structure Functions for the Bag Beyond Leading Order

Abstract

There has recently been surprising progress in understanding the spin and flavor dependence of deep inelastic structure functions in terms of the same physics needed in the simple quark models used for hadronic spectroscopy. However, the corresponding scale is usually very low, casting doubt on the use of leading order QCD evolution. We show that the conclusions are not significantly altered if one goes to next-to-leading order. In particular, the excellent agreement with unpolarized and polarized valence quark distributions is retained.

Nucleon and pion distribution functions in the valence region

“…The computation described in (Steffens and Thomas, 1995) is formulated with four parameters: a bag radius R; the masses of the two valence-diquark spectator states in an impulse approximation to the forward Compton scattering amplitude -scalar, M s , and axial-vector, M v (see Fig. VI.26); and the infrared resolving scale at which the computation is supposed to be valid, denoted by Q 0 above and µ therein.…”

“…Since this value of α(Q 0 ) might be considered too large for the fitting-by-evolution procedure to be valid, (Steffens and Thomas, 1995) (reduced by 20%) and material support only for x < 0.8 (domain contracted by 10%). These differences owe primarily to the accelerated production of sea-quarks through valence-quark depletion in NLO evolution as compared with the rate of this effect in LO evolution.…”

Polarized Deep Inelastic Scattering

“…Then all the curves for the polarized distributions shown in Ref. [35] are predictions of the model. In Fig.…”

“…That is to say, besides the many parametrizations for the polarized parton distributions [16], there are very few predictions based on a genuine model of the nucleon structure. We will show some results from the Adelaide group [34,35] noticing that there are others around. These calculations involved the use of bag model wave functions as an approximation for the proton wave function.…”

“…These calculations involved the use of bag model wave functions as an approximation for the proton wave function. The corresponding leading twist parton distributions were then evolved [35] in leading and next-to-leading order QCD evolution to the scale of the experiments. The resulting agreement between theory and experiment is very rewarding especially because of the simplicity of the model and the fact that all the free parameters were fixed in the unpolarized total valence distribution.…”