Measurement of $J/\psi$ at forward and backward rapidity in $p+p$, $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200$ GeV

Charmonium is a valuable probe in heavy-ion collisions to study the properties of the quark gluon plasma, and is also an interesting probe in small collision systems to study cold nuclear matter effects, which are also present in large collision systems. With the recent observations of collective behavior of produced particles in small system collisions, measurements of the modification of charmonium in small systems have become increasingly relevant. We present the results of $J/\psi$ measurements at forward and backward rapidity in various small collision systems, $p+p$, $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$, at $\sqrt{s_{{}_{NN}}}=200$ GeV. The results are presented in the form of the observable $R_{AB}$, the nuclear modification factor, a measure of the ratio of the $J/\psi$ invariant yield compared to the scaled yield in $p+p$ collisions. We examine the rapidity, transverse momentum, and collision centrality dependence of nuclear effects on $J/\psi$ production with different projectile sizes $p$ and ${}^3\mathrm{He}$, and different target sizes Al and Au. The modification is found to be strongly dependent on the target size, but to be very similar for $p+\mathrm{Au}$ and ${}^3\mathrm{He}+\mathrm{Au}$. However, for 0%–20% central collisions at backward rapidity, the modification factor for ${}^3\mathrm{He}+\mathrm{Au}$ is found to be smaller than that for $p+\mathrm{Au}$, with a mean fit to the ratio of $0.89\pm 0.03$(stat)$\pm 0.08$(syst), possibly indicating final state effects due to the larger projectile size.

Figure 1

Side view of the PHENIX detector in 2014 and 2015.

Figure 2

Invariant mass distributions of unlike-sign and like-sign dimuons in $p+p$ and integrated centrality of $p+\mathrm{Au}$ collisions in the south muon arm. Fit results to extract the $J/\psi$ signal are also presented.

Figure 3

Acceptance and reconstruction efficiency as a function of $p_T$ for dimuons from $J/\psi$ decays in $p+p$ collisions. geant4 simulations evaluate detector $\mathrm{acceptance}\times \mathrm{efficiency}$ simultaneously.

Figure 4

$J/\psi$ invariant yields as a function of $p_T$ in $p+p$ collisions at $\sqrt{s}=200\mathrm{GeV}$. The ratio between the values for the two muon arms is presented in the bottom panel. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties. There is also a global systematic uncertainty of 10.1%

Figure 5

Nuclear modification factor of inclusive $J/\psi$ as a function of rapidity for 0%–100% $p+\mathrm{Al}$ (a), $p+\mathrm{Au}$ (b), and ${}^3\mathrm{He}+\mathrm{Au}$ (c) collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties. The theory bands are discussed in the text.

Figure 6

Nuclear modification factor of inclusive $J/\psi$ as a function of rapidity in three centrality bins for $p+\mathrm{Al}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 7

Nuclear modification factor of inclusive $J/\psi$ as a function of rapidity in six centrality bins for $p+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 8

Nuclear modification factor of inclusive $J/\psi$ as a function of rapidity in three centrality bins for ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 9

Nuclear modification factor of inclusive $J/\psi$ as a function of $p_T$ at backward rapidity (Al/Au-going direction) for 0%–100% $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties. The theory bands are discussed in the text.

Figure 10

Nuclear modification factor of inclusive $J/\psi$ as a function of $p_T$ at forward rapidity ($p/{}^3\mathrm{He}$-going direction) for 0%–100% $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties. The theory bands are discussed in the text.

Figure 11

Nuclear modification factor of inclusive $J/\psi$ as a function of $p_T$ in three centrality bins for $p+\mathrm{Al}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 12

Nuclear modification factor of inclusive $J/\psi$ as a function of $p_T$ at $-2.2<y<-1.2$ in six centrality bins for $p+\mathrm{Au}$ collisions. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. The theory bands are discussed in the text. Note that the theory bands compared with the 0%–5% and 5%–10% centrality data are for 0%–10%.

Figure 13

Nuclear modification factor of inclusive $J/\psi$ as a function of $p_T$ at $1.2<y<2.2$ in six centrality bins for $p+\mathrm{Au}$ collisions. The theory bands are discussed in the text. Note that the theory bands compared with the 0%–5% and 5%–10% centrality data are for 0%–10%.

Figure 14

Nuclear modification factor of inclusive $J/\psi$ as a function of $p_T$ in three centrality bins for ${}^3\mathrm{He}+\mathrm{Au}$ collisions.

Figure 15

Comparison of nuclear modification factor of $J/\psi$ as a function of $p_T$ in 0%–20% centrality $p+\mathrm{Al}$ and $p+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 16

Comparison of nuclear modification factor of $J/\psi$ as a function of $p_T$ in 0%–20% centrality $d+\mathrm{Au}$ [10] and $p+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 17

Comparison of nuclear modification factor of $J/\psi$ as a function of $p_T$ in 0%–20% centrality $p+\mathrm{Au}$ and ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 18

Nuclear modification factor of $J/\psi$ as a function of $\langle N_{\mathrm{coll}}\rangle$ for $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 19

Nuclear modification factor of $J/\psi$ as a function of $\langle N_{\mathrm{coll}}\rangle$ for $p+\mathrm{Au}$ collisions compared with the transport model. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 20

Nuclear modification factor of $J/\psi$ as a function of the mean target thickness sampled by charmonium production in the centrality bin, for $p+\mathrm{Al}$, $p+\mathrm{Au}$ and ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 21

$\langle p_T^2\rangle$ of $J/\psi$ for $p_T<7\mathrm{GeV}/c$ as a function of $\langle N_{\mathrm{coll}}\rangle$ for $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represent point-to-point uncorrelated (correlated) uncertainties.

Figure 22

$J/\psi$ invariant yield as a function of $y$ in MB $p+p$, $p+\mathrm{Al}$, $p+\mathrm{Au}$, and ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. There is also a global uncertainty of 10.1%, 11.5%, 12.1%, and 12.2% corresponding to $p+p$, $p+\mathrm{Al}$, $p+\mathrm{Au}$ and ${}^3\mathrm{He}+\mathrm{Au}$ yields.

Figure 23

$J/\psi$ invariant yield as a function of $y$ in various centrality bins of $p+\mathrm{Al}$ collisions. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. There is also a global uncertainty of 13.6%, 12.2%, and 12.3% corresponding to 0%–20%, 20%–40%, and 40%–72% centrality.

Figure 24

$J/\psi$ invariant yield as a function of $y$ in various centrality bins of $p+\mathrm{Au}$ collisions. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. There is also a global uncertainty of 11.9%, 11.8%, 12.2%, 12.1%, 12.2%, and 14.0% corresponding to 0%–5%, 5%–10%, 10%–20%, 20%–40%, 40%–60%, and 60%–84% centrality.

Figure 25

$J/\psi$ invariant yield as a function of $y$ in various centrality bins of ${}^3\mathrm{He}+\mathrm{Au}$ collisions. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. There is also a global uncertainty of 12.7%, 12.6%, and 13.4% corresponding to 0%–20%, 20%–40%, and 40%–88% centrality.

Figure 26

$J/\psi$ invariant yield as a function of $p_T$ in various centrality bins of $p+\mathrm{Al}$ collisions, and the yields in each centrality bin are scaled for better visibility. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. There is also a global uncertainty of 10.2%, 10.3%, 10.9%, and 10.4% corresponding to 0%–20%, 20%–40%, 40%–72%, and 0%–100% centrality.

Figure 27

$J/\psi$ invariant yield as a function of $p_T$ in various centrality bins of $p+\mathrm{Au}$ collisions, and the yields in each centrality bin are scaled for better visibility. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. There is also a global uncertainty of 11.8% for 60%–84% centrality and 10.2% for all remaining centralities.

Figure 28

$J/\psi$ invariant yield as a function of $p_T$ in various centrality bins of ${}^3\mathrm{He}+\mathrm{Au}$ collisions, and the yields in each centrality bin are scaled for better visibility. Bars (boxes) around data points represents point-to-point uncorrelated (correlated) uncertainties. There is also a global uncertainty of 10.7% for 40%–88% centrality and 10.2% for all remaining centralities.