System size dependence of particle production and collectivity from the STAR experiment at RHIC

TL;DR

This paper investigates how particle production and collective behavior depend on system size in various collision systems at RHIC, providing new measurements that help understand medium modifications and collectivity origins.

Contribution

It presents the first measurements of centrality-dependent charged hadron production and nuclear modification factors in isobar collisions, and explores particle production and correlations in ultra-peripheral $b3$+Au events.

Findings

System size influences particle spectra and medium modification.

First measurements of $R_{AA}$ in isobar collisions.

Observation of long-range di-hadron correlations in $b3$+Au events.

Abstract

Medium modification of particle spectra and the origin of collectivity in small collision systems are widely debated topics in the heavy-ion community. To address these open questions, we propose the study of particle production and collectivity for varying system sizes,Au+Au $>$ Ru+Ru/Zr+Zr $>$ Cu+Cu $>$ d+Au $>$ $\gamma$+Au, available at RHIC using the STAR detector. We present the first measurements of centrality dependent charged hadron production in Isobar (Ru+Ru and Zr+Zr) collisions, including the nuclear modification factors ($R_\mathrm{AA}$) at high transverse momentom ($p_\mathrm{T}$), and identified particle spectra at low $p_\mathrm{T}$\ at mid-rapidity. Combined with existing results from other systems, they probe system size and collision geometry dependences of the medium modification to particle production. In addition, we present the measurement of particle production and long-range di-hadron correlations in $\gamma$+Au events using ultra-peripheral Au+Au collisions at RHIC.