Pre-defence seminar: The structure of the proton: quark and hadronic degrees of freedom

Seminar in preparation of a PhD defence, about theoretical hadron physics.

Abstract:

From a perturbative QCD point of view the dbar-ubar asymmetry observed in the proton sea is difficult to understand. We show that by also taking into account hadronic (baryon-meson) fluctuations of the proton, this problem has a natural solution and agreement with data is presented.

An outstanding problem that has evaded solution for several decades is the so-called `proton spin puzzle'. Data shows that the fraction ∆Σ of the proton's spin carried by its constituent quarks is quite small compared to what is predicted by the otherwise successful SU(6) quark-model of hadrons. We present here our Hadron-Cloud Model taking into account hadronic fluctuations, partonic degrees of freedom, relativistic effects and allow for SU(6) symmetry-breaking. With this we obtain good agreement with the polarized structure functions of both the proton and that of the neutron. Good agreement with the integrals of the polarized structure functions (and the related Bjorken sum-rule) is also presented. This yields a value of ∆Σ consistent with data.

Results on the strange-sea content of the proton is also presented.