  We investigate the dissociation of a heavy meson in the medium composed of
light quarks and gluons. In the quark-gluon plasma, the dissociation length of
the heavy meson becomes short as the temperature or quark chemical potential
increases. On the contrary, in the hadronic phase the dissociation length
becomes large as the chemical potential increases, due to the different
dissociation mechanism with one used in the quark-gluon plasma.
