  When an energetic parton traverses the hot QCD medium, it may suffer multiple
scattering and energy losses. The medium-induced gluon radiation for a massive
quark will be suppressed relative to that of a light quark due to the dead-cone
effect. The development of new declustering techniques of jet evolution makes a
direct study of the dead-cone effect in the QCD medium possible for the first
time. In this work, we compute the emission angle distribution of the
charm-quark initiated splittings in $\rm D^0$ meson tagged jet and that of the
light parton initiated splittings in inclusive jets in p+p and Pb+Pb at
$5.02$~TeV by utilizing the declustering techniques of jet evolution. The heavy
quark propagation and indued energy loss in the QCD medium are simulated with
the SHELL model based on the Langevin equation. When comparing the jet number
normalized emission angle distributions of the charm-quark initiated splittings
and that of the light parton initiated splittings by directly taking their
ratios at the same energy intervals of the initial parton, one can find the
charm-quark initiated splittings will be suppressed at smaller emission angle
corresponding to the dead-cone effect. The dead-cone effect of the jet
quenching can be directly observed. We further investigate the case of the
emission angle distributions normalized to the number of splittings in jets and
find that the dead-cone effect will broaden the emission angle of the splitting
and reduce the possibility of such splitting occurring, leading to the massive
parton losing less energy.
