Quantifying photoproduction corrections to $J/\psi$ measurements in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV

The contribution of $J/\psi$ production from coherent and incoherent photon-induced production is calculated in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV. The yield and nuclear modification factors $\left(R_{AA}\right)$ contributed by photoproduction are presented as functions of transverse momentum $\left(p_T\right)$ and centrality at both mid- and forward rapidity $\left(\mathrm{y}\right)$. The $R_{AA}$ of $J/\psi$ from photoproduction is found to be as high as 0.6 in the lowest $p_T$ bin ($0<p_T<1$ GeV/$c$) at midrapidity in 60–92% Au+Au collisions. The $R_{AA}$ measured in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV are corrected by subtracting the calculated photoproduction contribution.

Figure 1

Distributions of photon-induced $J/\psi$ invariant yield as a function of $-t\sim p_T^2$ for midrapidity ($\left|y\right|<1$) in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV with centralities of (a) 0–$20\%$, (b) 20–$40\%$, (c) 40–$60\%$, and (d) 60–$80\%$. The open circles represent STAR data taken from Ref. [26].

Figure 2

$dN/dy$ distributions of $J/\psi$ from coherent and incoherent photoproduction in (a) Au+Au and (b) Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV.

Figure 3

$J/\psi R_{AA}$ as a function of $p_T$ at both forward and midrapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV with various centralities. The solid circles and squares are shifted to the right by 0.1 GeV/$c$ for clarification.

Figure 4

$J/\psi R_{AA}$ as a function of $p_T$ at both forward and midrapidity in Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV with various centralities. The solid circles and squares are shifted to the right by 0.1 GeV/$c$ for clarification.

Figure 5

The $J/\psi p_T$-integrated $R_{AA}$ as a function of $N_{\mathrm{part}}$ in Au+Au (top) and Cu+Cu (bottom) collisions at $\sqrt{s_{NN}}=200$ GeV.