  In order to attribute the partonic energy loss experienced by jets (jet
quenching) observed in A+A collisions to the traversal of partons through the
hot QCD medium, it is necessary to examine the cold nuclear matter (CNM)
effects on the corresponding jets. Such an examination has historically been
done using $p$+A collisions. We present fully corrected measurements of the jet
mass and SoftDrop groomed jet mass in $p$+$p$ and $p$+Au collisions at STAR at
$\sqrt{s_{\rm{NN}}}=200$ GeV as a function of the event activity (EA) to
increase or decrease the magnitude of CNM effects. EA is determined in the
backward (Au-going) rapidity ($-5.0<\eta<-3.3$) by the STAR Beam-Beam Counter
to minimize auto-correlation with jets measured at mid-rapidity. Comparison of
the jet mass distribution in $p$+Au collisions to that in $p$+$p$ collisions
allows for isolation of CNM effects in anticipation of an upcoming jet mass
measurement in Au+Au collisions.
