Di-jet measurements in heavy-ion collisions at STAR

TL;DR

This paper reports on measurements of di-jet structures in heavy-ion collisions at STAR, revealing how jets lose energy in the quark-gluon plasma and how their properties differ from proton-proton collisions.

Contribution

It provides the first detailed measurements of fully reconstructed di-jets in Au+Au collisions at STAR, highlighting the effects of medium-induced energy loss.

Findings

Reconstructed di-jet structures show significant modifications in Au+Au compared to p+p.

Trigger bias selects jets with minimal medium interaction, emphasizing energy loss effects.

Results help quantify jet quenching and medium properties in heavy-ion collisions.

Abstract

Jets are produced from hard scatterings in the early stages of heavy-ion collisions. It is expected that these high-$p_T$ partons travel through the hot and dense medium before fragmenting. Therefore they are expected to suffer energy loss in the QGP via gluon radiation and elastic collisions along their path. Measurements of fully reconstructed jets help understand the effect of the energy loss on the jet structure and energy profile. A data-driven characterization of the background in Au+Au is needed in order to compare the results to p+p. The full azimuthal coverage of STAR Time Projection Chamber and Electromagnetic Calorimeter allows measurements of fully reconstructed di-jets, defined by jets that match the online trigger and recoil jets on the away side. A tight selection of the trigger jets allows for a selection of those coming from the surface. Hence, the population of jets on the recoil side is biased towards a maximal energy loss because of the extreme in-medium pathlength. We present measurements of di-jets, exploring their structure and properties in Au+Au and p+p at $\sqrt s_{NN}=$200 GeV in the STAR experiment.