  One key difference in current energy loss models lies in the treatment of the
Altarelli-Parisi, AP, splitting functions. It has been shown that the shared
momentum fraction, henceforth called Jet Splitting Function $z_g$ as determined
by the SoftDrop grooming process can be made a Sudakov-safe measurement of the
symmetrized AP functions in p+p collisions. The STAR collaboration presents the
first z_g measurements at $\sqrt{s_{NN}}=200$ GeV in p+p and Au+Au collisions,
where in Au+Au we use the specific di-jet selection introduced in our previous
momentum imbalance measurement. For a jet resolution parameter of $R=0.4$,
these di-jet pairs were found to be significantly imbalanced with respect to
p+p, yet regained balance when all soft constituents were included. We find
that within uncertainties there are no signs of a modified Jet Splitting
Function on trigger or recoil sides of this di-jet selection.
