Reconstruction of neutral-triggered charged recoil jets in √s = 200 GeV p+p collisions at the STAR experiment

Derek Anderson

doi:10.1051/epjconf/202023505005

Abstract

Jets — collimated sprays of hadrons — are produced by hard-scattered partons during the early stages of heavy ion collisions. Hence, they provide a valuable probe of the complex multi-particle dynamics within the hot, dense medium produced in such collisions. In particular, the study of jets recoiling from direct photons (γdir+jet) and those recoiling from energetic π0 (π0+jet) may shed light on the path-length and initial flavor (quark vs. gluon) dependence of the energy-loss experienced by a parton as it traverses the medium. We present here measurements of the yields of charged recoil jets tagged by γdir and π0 in p+p collisions at √S = 200 GeV. These measurements will serve as a vacuum fragmentation reference for an upcoming measurement in Au + Au collisions.

Highlights

The collisions of ultra-relativistic heavy ions such as the Au+Au collisions studied at the Relativistic Heavy-Ion Collider (RHIC) produce an extremely hot, dense medium with properties consistent with those expected of a liquid of deconfined partons, the Quark-Gluon Plasma (QGP)
The recoil jets tagged γdir are predominantly fromquarks. These two observations, that energetic π0 are biased towards surface production and that γdirtagged jets predominantly originate fromquarks, suggest that energy loss experienced by the recoil jets may differ between the two systems
Candidate triggers are identified as one to two Barrel (i.e. mid-rapidity) Electromagnetic Calorimeter (BEMC) tower clusters with transverse energy in the range of ETtrg ∈ (9, 20) GeV and a centroid whose pseudorapidity lies in the range |ηtrg| < 0.9

Summary

Introduction

The collisions of ultra-relativistic heavy ions such as the Au+Au collisions studied at the Relativistic Heavy-Ion Collider (RHIC) produce an extremely hot, dense medium with properties consistent with those expected of a liquid of deconfined partons, the Quark-Gluon Plasma (QGP). Jets are powerful probes due to the large momentum-transfers involved in their production, which makes them amenable to a perturbative QCD description They are produced in the earliest stages of the collisions and so are expected to be sensitive to the evolution of the medium. The recoil jets tagged γdir are predominantly from (anti-)quarks These two observations, that energetic π0 are biased towards surface production and that γdirtagged jets predominantly originate from (anti-)quarks, suggest that energy loss experienced by the recoil jets may differ between the two systems. This suppression is quantified by IAA ≡ DAu+Au/Dp+p, where DAu+Au and Dp+p are the per-trigger yields of recoil jets in Au+Au and p+p, respectively Presented in these proceedings are measurements of the γdir- and π0-tagged per-trigger charged recoil jet spectra in p+p collisions (Dp+p), which will serve as vacuum-fragmentation (no medium) baselines for future measurements of IAA

The STAR Detector

Corrected Recoil Jet Spectra

Summary and Future Work