Production of Jets at STAR

TL;DR

This paper presents recent measurements of charged-particle jets at STAR across different collision systems, providing insights into jet quenching, medium modification, and QCD phenomena in both vacuum and hot dense media.

Contribution

It offers new experimental data on jet properties and correlations in p+Au and Au+Au collisions, enhancing understanding of jet quenching and medium effects at RHIC energies.

Findings

High-$p_T$ jets inversely related to event activity in p+Au

No significant jet quenching observed in high-EA p+Au collisions

Jet suppression and broadening studied in Au+Au collisions

Abstract

Jets serve as an important tool to probe QCD both in the vacuum and in the hot and dense medium. The STAR experiment at RHIC plays a key role in studying QCD phenomena across different collision systems ($p$+$p$, $p$+A, A+A), offering access to a kinematic regime that complements that of the LHC. Building on recent jet and event activity studies at STAR, we present recent measurements on charged-particle jets at $\sqrt{s_{\mathrm{NN}}}~=~200$ GeV. In $p$+Au collisions, we explore event activity (EA) measured in the Au-going direction and its correlation with particle production at mid-rapidity. While soft particle production increases with EA, high-$p_{\mathrm{T}}$ jets are found to be inversely related to EA. Ratios of $p_{\mathrm{T}}$ imbalance and azimuthal dijet separation between high- and low-EA events show no significant differences, suggesting no strong evidence of jet quenching in high-EA $p$+Au collisions. In Au+Au collisions, we report semi-inclusive measurements of jets recoiling from $\gamma$ and $\pi^0$ triggers, using mixed-event techniques to subtract background and study jet suppression, intra-jet broadening, and acoplanarity. Additionally, we present inclusive charged-particle jet spectra corrected for background fluctuations, extending the kinematic reach of previous measurements. These results provide crucial insight into the modification of jets in the medium and contribute to a deeper understanding of QCD in heavy-ion collisions.