Quark structure of the pion and pion form factor

Abstract

We consider the pion structure in the region of low and moderately high momentum transfers: at low $Q^2$, the pion is treated as a composite system of constituent quarks; at moderately high momentum transfers, $Q^2=10\div25\;GeV^2$, the pion \ff is calculated within perturbative QCD taking into account one--gluon hard exchange. Using the data on pion \ff at $Q^2<3\;GeV^2$ and pion axial--vector decay constant, we reconstruct the pion \wf in the soft and intermediate regions. This very wave function combined with one--gluon hard scattering amplitude allows a calculation of the pion \ff in the hard region $Q^2=10\div25\;GeV^2$. A specific feature of the reconstructed pion \wf is a quasi--zone character of the $q\bar q$--excitations. On the basis of the obtained pion \wf and the data on deep inelastic scattering off the pion, the valence quark distribution in a constituent quark is determined.