Forward $J/\psi$ production in U$+$U collisions at $\sqrt{s_{NN}}$=193 GeV

TL;DR

This study measures $J/$ production in U+U collisions at 193 GeV, comparing it with Au+Au collisions to understand suppression and coalescence effects at different centralities.

Contribution

It provides new measurements of $J/$ yields and nuclear modification factors in U+U collisions, and investigates the impact of different Glauber model parameterizations on collision scaling.

Findings

$J/$ suppression is similar in U+U and Au+Au for peripheral and midcentral collisions.

Less suppression of $J/$ observed in the most central U+U collisions.

Results suggest $car{c}$ coalescence plays a significant role in $J/$ production at high energy densities.

Abstract

The invariant yields for $J/\psi$ production at forward rapidity $(1.2<|y|<2.2)$ in U$+$U collisions at $\sqrt{s_{_{NN}}}$=193 GeV have been measured as a function of collision centrality. The invariant yields and nuclear-modification factor $R_{AA}$ are presented and compared with those from Au$+$Au collisions in the same rapidity range. Additionally, the direct ratio of the invariant yields from U$+$U and Au$+$Au collisions within the same centrality class is presented, and used to investigate the role of $c\bar{c}$ coalescence. Two different parameterizations of the deformed Woods-Saxon distribution were used in Glauber calculations to determine the values of the number of nucleon-nucleon collisions in each centrality class, $N_{\rm coll}$, and these were found to give significantly different $N_{\rm coll}$ values. Results using $N_{\rm coll}$ values from both deformed Woods-Saxon distributions are presented. The measured ratios show that the $J/\psi$ suppression, relative to binary collision scaling, is similar in U$+$U and Au$+$Au for peripheral and midcentral collisions, but that $J/\psi$ show less suppression for the most central U$+$U collisions. The results are consistent with a picture in which, for central collisions, increase in the $J/\psi$ yield due to $c\bar{c}$ coalescence becomes more important than the decrease in yield due to increased energy density. For midcentral collisions, the conclusions about the balance between $c\bar{c}$ coalescence and suppression depend on which deformed Woods-Saxon distribution is used to determine $N_{\rm coll}$.