  The color field of a quark, stripped off in a hard reaction, is regenerated
via gluon radiation. The space-time development of a jet is controlled by the
coherence time of gluon radiation, which for heavy quarks is subject to the
dead-cone effect, suppressing gluons with small transverse momenta. As a
result, heavy quarks can radiate only a small fraction of the initial energy.
This explains the peculiar shape of the measured heavy quark fragmentation
function, which strongly peaks at large fractional momenta z. The fragmentation
length distribution, related to the fragmentation function in a model
independent way, turns out to be concentrated at distances much shorter than
the confinement radius. This implies that the mechanisms of heavy quark
fragmentation is pure perturbative.
