# Measurements of double-helicity asymmetries in inclusive $J/\psi$ production in longitudinally polarized $p+p$ collisions at $\sqrt{s}=510$ GeV

Abstract : We report the double helicity asymmetry, $A_{LL}^{J/\psi}$, in inclusive $J/\psi$ production at forward rapidity as a function of transverse momentum $p_T$ and rapidity $|y|$. The data analyzed were taken during $\sqrt{s}=510$ GeV longitudinally polarized $p$+$p$ collisions at the Relativistic Heavy Ion Collider (RHIC) in the 2013 run using the PHENIX detector. At this collision energy, $J/\psi$ particles are predominantly produced through gluon-gluon scatterings, thus $A_{LL}^{J/\psi}$ is sensitive to the gluon polarization inside the proton. We measured $A_{LL}^{J/\psi}$ by detecting the decay daughter muon pairs $\mu^+ \mu^-$ within the PHENIX muon spectrometers in the rapidity range $1.2<|y|<2.2$. In this kinematic range, we measured the $A_{LL}^{J/\psi}$ to be $0.012 \pm 0.010$~(stat)~$\pm$~$0.003$(syst). The $A_{LL}^{J/\psi}$ can be expressed to be proportional to the product of the gluon polarization distributions at two distinct ranges of Bjorken $x$: one at moderate range $x \approx 0.05$ where recent RHIC data of jet and $\pi^0$ double helicity spin asymmetries have shown evidence for significant gluon polarization, and the other one covering the poorly known small-$x$ region $x \approx 2\times 10^{-3}$. Thus our new results could be used to further constrain the gluon polarization for $x< 0.05$.
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Journal articles
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http://hal.in2p3.fr/in2p3-01333933
Contributor : Sophie Heurteau <>
Submitted on : Monday, June 20, 2016 - 11:06:03 AM
Last modification on : Tuesday, November 19, 2019 - 2:37:40 AM

### Citation

A. Adare, C. Aidala, N. N. Ajitanand, Y. Akiba, R. Akimoto, et al.. Measurements of double-helicity asymmetries in inclusive $J/\psi$ production in longitudinally polarized $p+p$ collisions at $\sqrt{s}=510$ GeV. Physical Review D, American Physical Society, 2016, 94, pp.112008 ⟨10.1103/PhysRevD.94.112008⟩. ⟨in2p3-01333933⟩

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