  We present the medium-modified energy collimation in the leading-logarithmic
approximation (LLA) and next-to-leading-logarithmic approximation (NLLA) of
QCD. As a consequence of more accurate kinematic considerations in the argument
of the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) fragmentation
functions (FFs) we find a new NLLA correction ${\cal O}(\alpha_s)$ which
accounts for the scaling violation of DGLAP FFs at small $x$. The jet shape is
derived from the energy collimation within the same approximations and we also
compare our calculations for the energy collimation with the event generators
Pythia 6 and YaJEM for the first time in this paper. The modification of jets
by the medium in both cases is implemented by altering the infrared sector
using the Borghini-Wiedemann model. The energy collimation and jet shapes
qualitatively describe a clear broadening of showers in the medium, which is
further supported by YaJEM in the final comparison of the jet shape with CMS
PbPb data at center-of-mass energy 2.76 TeV. The comparison of the biased
versus unbiased YaJEM jet shape with the CMS data shows a more accurate
agreement for biased showers and illustrates the importance of an accurate
simulation of the experimental jet-finding strategy.
