Jet substructure in $p$+$p$ and $p$+Au collisions at $\sqrt{s_{\text{NN}}} = 200$ GeV at STAR

Abstract

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.