System size and energy dependence of near-side di-hadron correlations

TL;DR

This study analyzes near-side di-hadron correlations across different collision systems and energies, revealing consistent jet-like behavior and energy-dependent ridge phenomena, providing insights into particle production mechanisms in heavy-ion collisions.

Contribution

It presents the first systematic comparison of near-side correlations in d+Au, Cu+Cu, and Au+Au collisions at two energies, highlighting the system size and energy dependence of the ridge and jet-like components.

Findings

Jet-like correlation width increases with system size.

Ridge is present in Cu+Cu and lower energy collisions.

Ridge magnitude is smaller at 62.4 GeV compared to 200 GeV.

Abstract

Two-particle azimuthal ($\Delta\phi$) and pseudorapidity ($\Delta\eta$) correlations using a trigger particle with large transverse momentum ($p_T$) in $d$+Au, Cu+Cu and Au+Au collisions at $\sqrt{s_{{NN}}}$ =\xspace 62.4 GeV and 200~GeV from the STAR experiment at RHIC are presented. The \ns correlation is separated into a jet-like component, narrow in both $\Delta\phi$ and $\Delta\eta$, and the ridge, narrow in $\Delta\phi$ but broad in $\Delta\eta$. Both components are studied as a function of collision centrality, and the jet-like correlation is studied as a function of the trigger and associated $p_T$. The behavior of the jet-like component is remarkably consistent for different collision systems, suggesting it is produced by fragmentation. The width of the jet-like correlation is found to increase with the system size. The ridge, previously observed in Au+Au collisions at $\sqrt{s_{{NN}}}$ = 200 GeV, is also found in Cu+Cu collisions and in collisions at $\sqrt{s_{{NN}}}$ =\xspace 62.4 GeV, but is found to be substantially smaller at $\sqrt{s_{{NN}}}$ =\xspace 62.4 GeV than at $\sqrt{s_{{NN}}}$ = 200 GeV for the same average number of participants ($ \langle N_{\mathrm{part}}\rangle$). Measurements of the ridge are compared to models.