  This paper concerns a method of describing hadrons that starts with the
canonical front form Hamiltonian of QCD. The method is developed in the
relatively simple context of QCD with only heavy quarks. We regulate its
canonical Hamiltonian by introducing a vanishingly small gluon mass $m_g$. For
positive $m_g$, the small-$x$ gluon divergences become ultraviolet and hence
they are renormalized in the same way the ultraviolet transverse divergences
are. This is done using the renormalization group procedure for effective
particles. Up to the second order of expansion of the renormalized Hamiltonian
in powers of the quark-gluon coupling constant $g$, only the quark mass-squared
and gluon-exchange divergences require counter terms. In these circumstances,
we calculate an effective potential between quarks in heavy quarkonia in an
elementary way, replacing all the quarkonium-state components with gluons of
mass $m_g$ by only one component with just one gluon that is assigned a mass
$m_G$, comparable to or exceeding the scale of typical relative momenta of
bound quarks. In the limit of $m_g \to 0$ and large $m_G$ two results are
obtained. (1) While the color-singlet quarkonium mass eigenvalue stays finite
and physically reasonable in that limit, the eigenvalues for single quarks and
octet quarkonia are infinite. (2) The effective quark-antiquark potential is
quadratic as a function of the distance and spherically symmetric for typical
separations between quarks but becomes logarithmic and no longer spherically
symmetric for large separations. Our conclusion indicates how to systematically
improve upon the approximations made in this paper.
