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Geometry-induced azimuthal anisotropy in coherent J/ψ photoproduction

Ding Yu Shao1,2,*, Han-Qing Yu1,†, Cheng Zhang3,‡, and Jian Zhou4,5,§

  • 1Department of Physics, Center for Field Theory and Particle Physics, Key Laboratory of Nuclear Physics and Ion-beam Application (MOE), Fudan University, Shanghai 200433, China
  • 2Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University, Shanghai 200438, China
  • 3School of Physics, Hangzhou Normal University, Hangzhou, Zhejiang 311121, China
  • 4Key Laboratory of Particle Physics and Particle Irradiation (MOE), Institute of Frontier and Interdisciplinary Science, Shandong University, (QingDao), Shandong 266237, China
  • 5Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences, HuiZhou, Guangdong 516000, China

  • *Contact author: dingyu.shao@cern.ch
  • †Contact author: yuhq24@m.fudan.edu.cn
  • ‡Contact author: chengzhang@hznu.edu.cn
  • §Contact author: jzhou@sdu.edu.cn
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Phys. Rev. D 113, 094022 – Published 18 May, 2026

DOI: https://doi.org/10.1103/fhks-8s8z

Abstract

Azimuthal anisotropies in heavy-ion collisions are conventionally interpreted as signatures of hydrodynamic flow. We demonstrate that in peripheral collisions, a significant cos2ϕ asymmetry in the decay leptons of coherently photoproduced J/ψ mesons arises purely from the initial-state geometry of the nuclear electromagnetic field. This modulation originates from the linear polarization of coherent photons, which is radially aligned in impact parameter space and transferred to the vector meson. By employing light-cone perturbation theory within the dipole formalism, we calculate the centrality dependence of this asymmetry for collisions at RHIC and LHC energies. Our predictions quantitatively reproduce STAR data. This observable thus provides a rigorous benchmark for distinguishing electromagnetic initial-state effects from collective medium dynamics.

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Phys. Rev. D 113, 094022– Published 18 May, 2026
  • Received 30 November 2025
  • Accepted 23 February 2026
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