J/$\psi$ and $\psi$(2S) Production in Small Systems with PHENIX

TL;DR

This paper reports on measurements of J/ψ and ψ(2S) production in small collision systems at RHIC, revealing differential suppression patterns that suggest the presence of final state effects previously observed mainly in larger systems.

Contribution

It provides new experimental data on charmonium production in small systems at RHIC energies, highlighting the role of final state effects in ψ(2S) suppression.

Findings

Differential suppression of ψ(2S) observed in small systems.

Nuclear modification factors vary with centrality and rapidity.

Results align with some model predictions and differ from others.

Abstract

The suppression of the $\psi$(2S) nuclear modification factor has been seen as a trademark signature of final state effects in large collision systems for decades. In small systems, deviations of the nuclear modification from unity had been attributed to cold nuclear matter effects until the observation of strong differential suppression of the $\psi$(2S) state in $p/d+$A collisions, which suggests the presence of final state effects. In this paper, we present results of J/$\psi$ and $\psi$(2S) measurements in the dimuon decay channel for $p+p$, $p+$Al, and $p+$Au collision systems at $\sqrt{s_{_{NN}}}$ = 200 GeV. Key results include the nuclear modification factors $R_{pA}$ as a function of centrality and rapidity. The measurements are compared with shadowing and transport model predictions, as well as to complementary measurements at LHC energies.