  We present a description of vacuum polarization in a circular Dirac quantum
dot in two spatial dimensions assuming $\alpha$ - the relative strength of the
Coulomb interaction small enough to render an approximation with a single
electron (hole) lowest energy level relevant. Applying this approximation, we
find that for $ \alpha_c \approx 1.05$ the lowest level is half-filled
irrespective of the number of flavors that are present. The ground state can be
represented as a superposition of particular (even number) excitonic states
which constitute an excitonic cloud that evolves in a crossover manner. The
ground state is degenerate with an intervalley excitonic state at $ \alpha_c
\approx 1.05$, a critical strength, that in our approximation marks a point
with single electron and exciton resonances.
