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

The PHENIX Collaboration has measured the ratio of the yields of $\psi \left(2S\right)$ to $\psi \left(1S\right)$ mesons produced in $p+p$, $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{\mathit{NN}}}}=200$ GeV over the forward and backward rapidity intervals $1.2<\left|y\right|<2.2$. 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 ${}^3\mathrm{He}$-going) direction, the relative yield of $\psi \left(2S\right)$ mesons to $\psi \left(1S\right)$ mesons is consistent with the value measured in $p+p$ collisions. However, in the backward (nucleus-going) direction, the $\psi \left(2S\right)$ meson is preferentially suppressed by a factor of $\sim 2$. This suppression is attributed in some models to the breakup of the weakly bound $\psi \left(2S\right)$ meson 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.

Figure 1

The measured dimuon mass spectra with fits from the (a)–(d) South and (e)–(h) North PHENIX muon arms, for $p+p$, $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions at $\sqrt{s_{{}_{\mathit{NN}}}}$ = 200 GeV. The total fit is the solid (black) line with a shaded (gray) band representing the 90% confidence level. The dashed (blue) and dotted (red) lines represent the contributions from the resonances and the background, respectively.

Figure 2

Comparison of world data on the ratio of $\psi \left(2S\right)/\psi \left(1S\right)$ mesons in dilepton decays [21, 29, 36, 37, 38, 39, 40, 41, 42].

Figure 3

Comparison of world data on the ratio of $\psi \left(2S\right)/\psi \left(1S\right)$ mesons as a function of $p_T$ [29, 40, 43, 44, 45], along with a calculation from a color evaporation model (CEM) at $\sqrt{s}=200$ GeV [25].

Figure 4

The double ratio of $\psi \left(2S\right)/\psi \left(1S\right)$ mesons measured in $p/d/{}^3\mathrm{He}+A$ collisions to that same ratio in $p+p$ collisions at $\sqrt{s}$ = 200 GeV, with a calculation based on breakup by comoving particles [47]. The bars (boxes) on the data points represent the statistical (systematic) uncertainties, and the shaded (open) box around unity represents the global uncertainty on the forward and backward (mid) rapidity data.

Figure 5

The double ratio of $\psi \left(2S\right)/\psi \left(1S\right)$ mesons measured in $p/{}^3\mathrm{He}+A$ collisions to that same ratio in $p+p$ collisions as a function of comoving particle density. The shaded (black) [open (green)] box around unity represents the global uncertainty on the PHENIX (ALICE) data.