Nuclear Experiment
[Submitted on 19 Nov 2021 (v1), last revised 22 Aug 2022 (this version, v2)]
Title:Evidence for Nonlinear Gluon Effects in QCD and their $A$ Dependence at STAR
View PDFAbstract:The STAR Collaboration reports measurements of back-to-back azimuthal correlations of di-$\pi^0$s produced at forward pseudorapidities ($2.6<\eta<4.0$) in $p$+$p$, $p+$Al, and $p+$Au collisions at a center-of-mass energy of 200 GeV. We observe a clear suppression of the correlated yields of back-to-back $\pi^0$ pairs in $p+$Al and $p+$Au collisions compared to the $p$+$p$ data. The observed suppression of back-to-back pairs as a function of transverse momentum suggests nonlinear gluon dynamics arising at high parton densities. The larger suppression found in $p+$Au relative to $p+$Al collisions exhibits a dependence of the saturation scale, $Q_s^2$, on the mass number, $A$. A linear scaling of the suppression with $A^{1/3}$ is observed with a slope of $-0.09$ $\pm$ $0.01$.
Submission history
From: Xiaoxuan Chu [view email][v1] Fri, 19 Nov 2021 19:19:34 UTC (149 KB)
[v2] Mon, 22 Aug 2022 18:33:47 UTC (264 KB)
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