Cold Nuclear Matter Effects on Inclusive $J/\psi$ Production in $p+\text{Au}$ Collisions at $\sqrt{s_\text{NN}}$ = 200 GeV with the STAR Experiment

TL;DR

This study measures inclusive $J/ar{J}$ production in proton-gold collisions at 200 GeV to investigate cold nuclear matter effects, finding no significant modification in the observed kinematic range.

Contribution

It provides the first detailed $R_{p ext{Au}}$ measurement for $J/ar{J}$ at 200 GeV with improved precision, testing CNM effects and model predictions.

Findings

$R_{p ext{Au}}$ is consistent with unity, indicating negligible CNM effects.

Model calculations agree with $R_{p ext{Au}}$ but not with individual yields.

Enhanced precision in cross-section and invariant-yield measurements.

Abstract

In this paper, a study of cold nuclear matter (CNM) effects is reported based on the new STAR measurement of inclusive $J/\psi$ production in $p+p$ and $p+\text{Au}$ collisions at $\sqrt{s_\text{NN}}$ = 200 GeV, and a combined $J/\psi\rightarrow e^{+}e^{-}$ cross section in $p+p$ collisions at $\sqrt{s}$ = 200 GeV is provided. Given the long-established presumption that the energy density and the temperature produced in proton-nucleon collisions are insufficient to form QGP droplets, CNM effects in $p+\text{Au}$ collisions are quantified by the nuclear modification factor ($R_{p\text{Au}}$), defined as the ratio of the yield of the inclusive $J/\psi$ in $p+\text{Au}$ collisions to that in $p+p$ collisions, scaled by the average number of binary nucleon-nucleon collisions. The $R_{p\text{Au}}$ is derived as a function of transverse momentum ($p_\text{T}$) in the range 4--12 GeV/$c$ and is averaged within the rapidity ($y$) and azimuthal angle ($\varphi$) coverage of $|y|<1$, $0 \leq \varphi < 2\pi$. The result is consistent with unity, suggesting negligible modification of the yield by CNM effects in this kinematic region. Various model calculations are in agreement with the $R_{p\text{Au}}$ measurement, yet the same calculations are less satisfactory in describing the individual invariant yields from $p+p$ and $p+\text{Au}$ collisions. In the covered kinematic region, this analysis has improved the precision of cross-section and invariant-yield measurements in $p+p$ and $p+\text{Au}$ collisions, respectively, and consequently the $R_{p\text{Au}}$.