  Heavy and light quarks produced in high-$p_T$ partonic collisions radiate
differently. Heavy quarks regenerate their color field, stripped-off in the
hard reaction, much faster than the light ones and radiate a significantly
smaller fraction of the initial quark energy. This peculiar feature of
heavy-quark jets leads to a specific shape of the fragmentation functions
observed in $e^+e^-$ annihilation. Differently from light flavors, the heavy
quark fragmentation function strongly peaks at large fractional momentum $z$,
i.e. the produced heavy-light mesons, $B$ or $D$, carry the main fraction of
the jet momentum. This is a clear evidence of the dead-cone effect, and of a
short production time of a heavy-light mesons. Contrary to propagation of a
small $q\bar q$ dipole, which survives in the medium due to color transparency,
a heavy-light $Q\bar q$ dipole promptly expands to a large size. Such a big
dipole has no chance to remain intact in a dense medium produced in
relativistic heavy ion collisions. On the other hand, a breakup of such a
dipole does not affect much the production rate of $Q\bar q$ mesons,
differently from the case of light $q\bar q$ meson production.
