  The production of the $\rho^o$- meson in the inclusive proton-proton
scattering $p_A+p_B\to \rho^o+X$ is studied using extension of parton model
according to generalized vector meson dominance model (GVMD) in region of small
$Q^2=m_{\rho^o}^2$ and $\rho^o$-meson transverse momentum $\le 1-2GeV/c$. The
realistic description of the experimental cross sections of $p_A+p_B\to
\rho^o+X$ for $4.9\le \sqrt{s}\le 65 GeV$ is achieved using an isotropic
distribution of the $\rho^o$-meson. The resulting density matrix allows one to
select values of the quark masses, which lead to the isotropic distribution of
the emitted meson. It is demonstrated that the same cross sections of the
reaction $p_A+p_B\to\rho^o +X$ for the isotropic distribution of the
$\rho^o$-meson can be obtained with different sets of the quark masses and
corresponding coupling constants of the quark-meson vertex functions.
