Method for separating jets and the underlying event in heavy ion collisions at the BNL Relativistic Heavy Ion Collider

Abstract

Reconstructed jets in heavy ion collisions are a crucial tool for understanding the quark-gluon plasma. The separation of jets from the underlying event is necessary particularly in central heavy ion reactions in order to quantify medium modifications of the parton shower and the response of the surrounding medium itself. There have been many methods proposed and implemented for studying the underlying event substructure in proton-proton and heavy ion collisions. In this paper, we detail a method for understanding underlying event contributions in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV utilizing the HIJING event generator. This method, extended from previous work by the ATLAS collaboration, provides a well-defined association of "truth jets" from the fragmentation of hard partons with "reconstructed jets" using the anti-$k_T$ algorithm. Results presented here are based on an analysis of 750M minimum bias HIJING events. We find that there is a substantial range of jet energies and radius parameters where jets are well separated from the background fluctuations (often termed "fake jets") that make jet measurements at RHIC a compelling physics program.