  In these proceedings, we discuss the role of heavy quark mass on the
formation of parton showers. Mass effects are not well understood when parton
branching occurs in nuclear matter, such as the quark-gluon plasma. Recently, a
theoretically consistent picture of open heavy flavor production in ultra
relativistic nuclear collisions has begun to emerge based on effective theories
of QCD, such as soft collinear effective theory with Glauber gluons. We show
that implementation of in-medium splitting processes containing heavy quarks
into next-to-leading order calculations of heavy flavor production leads to
larger cross section suppression when compared to traditional energy loss
phenomenology. To better constrain the important mass dependence of in-medium
splitting functions, we propose a new measurement in relativistic heavy ion
collisions, based on a two-prong structure inside a reconstructed heavy flavor
jet. In the region of jet transverse momenta where parton mass effects are
leading, we predict a unique reversal of the mass hierarchy of jet quenching
effects in heavy ion relative to proton collisions. We find that the momentum
sharing distribution of prompt $b$-tagged jets is more strongly modified in
comparison to the one for light jets. The work summarized here opens new
directions of research on the substructure of heavy flavor jets.
