System size dependence of two-particle angular correlations in p+p, Cu+Cu and Au+Au collisions

TL;DR

This study analyzes two-particle angular correlations across different collision systems and centralities, revealing a geometric scaling of cluster size that informs understanding of hadronization in dense media.

Contribution

It introduces a comprehensive analysis of cluster sizes in p+p, Cu+Cu, and Au+Au collisions, highlighting a geometric scaling relation and its implications for hadronization.

Findings

Cluster size is similar in semi-central Cu+Cu, Au+Au, and p+p collisions.

Cluster size increases as collisions become more peripheral.

A geometric scaling of cluster size with the fraction of total cross section is observed.

Abstract

We present a systematic study of two-particle angular correlations in p+p, Cu+Cu and Au+Au collisions over a broad range of pseudorapidity and azimuthal angle. The PHOBOS detector has a uniquely large angular coverage for inclusive charged particles, which allows for the study of correlations on both long- and short-range scales. A complex two-dimensional correlation structure emerges which is interpreted in the context of a cluster model. The cluster size and its decay width are extracted from the two-particle pseudorapidity correlation function. The cluster size found in semi-central Cu+Cu and Au+Au collisions is comparable to that found in p+p but a non-trivial increase of cluster size with decreasing centrality is observed. Moreover, the comparison between Cu+Cu and Au+Au systems shows an interesting scaling of the cluster size with the measured fraction of total cross section (which is related to $b/2R$), suggesting a geometric origin. These results should provide insight into the hadronization stage of the hot and dense medium created in heavy ion collisions.