Quark structure of the pion and pion form factor.

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 ÷ 25 GeV 2 , the pion form factor is calculated within perturbative QCD taking into account one–gluon hard exchange. Using the data on pion form factor at Q 2 < 3 GeV 2 and pion axial–vector decay constant, we reconstruct the pion wave function in the soft and intermediate regions. This very wave function combined with one–gluon hard scattering amplitude allows a calculation of the pion form factor in the hard region Q 2 = 10 ÷ 25 GeV 2. A specific feature of the reconstructed pion wave function is a quasi–zone character of the q ¯ q–excitations. On the basis of the obtained pion wave function and the data on deep inelastic scattering off the pion, the valence quark distribution in a constituent quark is determined.