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

TL;DR

This paper presents measurements of jet mass and SoftDrop groomed jet mass in proton-proton and proton-gold collisions at 200 GeV to study cold nuclear matter effects, aiding the understanding of jet quenching in heavy-ion collisions.

Contribution

It provides the first fully corrected jet mass measurements in $p$+$p$ and $p$+Au collisions at STAR, focusing on event activity dependence to isolate cold nuclear matter effects.

Findings

Jet mass distributions are measured and compared between $p$+$p$ and $p$+Au collisions.

Results help distinguish cold nuclear matter effects from hot medium effects in jet quenching.

The study sets the stage for future jet mass measurements in Au+Au collisions.

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.