Measurement of the relative yields of $\psi(2S)$ to $\psi(1S)$ mesons produced at forward and backward rapidity in $p$$+$$p$, $p$$+$Al, $p$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV

TL;DR

This study measures the ratio of $ ext{ψ(2S)}$ to $ ext{ψ(1S)}$ mesons in various small collision systems at 200 GeV, revealing a significant suppression of $ ext{ψ(2S)}$ in the nucleus-going direction, likely due to final state interactions.

Contribution

It provides the first detailed measurement of the $ ext{ψ(2S)}/ ext{ψ(1S)}$$ ratio across different small collision systems at RHIC energies, highlighting directional suppression effects.

Findings

$ ext{ψ(2S)}/ ext{ψ(1S)}$ ratio in $p+p$ collisions matches other energies.

No suppression of $ ext{ψ(2S)}$ in the forward direction.

Approximately 50% suppression of $ ext{ψ(2S)}$ in the backward (nucleus-going) direction.

Abstract

The PHENIX Collaboration has measured the ratio of the yields of $\psi(2S)$ to $\psi(1S)$ mesons produced in $p$$+$$p$, $p$$+$Al, $p$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV over the forward and backward rapidity intervals $1.2<|y|<2.2$. We find that the ratio in $p$$+$$p$ collisions is consistent with measurements at other collision energies. In collisions with nuclei, we find that in the forward ($p$-going or $^{3}$He-going) direction, the relative yield of $\psi(2S)$ mesons to $\psi(1S)$ mesons is consistent with the value measured in \pp collisions. However, in the backward (nucleus-going) direction, the $\psi(2S)$ is preferentially suppressed by a factor of $\sim$2. This suppression is attributed in some models to breakup of the weakly-bound $\psi(2S)$ through final state interactions with comoving particles, which have a higher density in the nucleus-going direction. These breakup effects may compete with color screening in a deconfined quark-gluon plasma to produce sequential suppression of excited quarkonia states.