Photon-induced J/ψ as a linearly polarized probe of collision geometry in relativistic heavy-ion collisions
Abstract
In relativistic heavy-ion collisions, the linear polarization of quasi-real photons can correlate the spin orientation of photon-induced vector mesons with the collision geometry. To explore this sensitivity, we present the first measurement of the decay angular distribution of photon-induced J/ψ with respect to the event plane in heavy-ion collisions with hadronic overlap. The analysis uses Ru+Ru and Zr+Zr collisions at a nucleon--nucleon center-of-mass energy of √(sNN)=200 GeV recorded by STAR. After correcting for the finite event-plane resolution and subtracting the residual hadronic contribution, we extract a negative second-order modulation, A2phot = −0.39 ± 0.11 (stat.) ± 0.04 (sys.), for |yee|<0.8, pTee<0.2 GeV/c, and 30--80% centrality. This modulation provides evidence that the J/ψ polarization is correlated with the event plane, as expected for linearly polarized photons. The observed modulation establishes polarized J/ψ photoproduction as a direct probe of the transverse orientation of the initial collision geometry.
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BibTeX
@misc{collaboration2026photoninduced,
title = {{Photon-induced $J/ψ$ as a linearly polarized probe of collision geometry in relativistic heavy-ion collisions}},
author = {STAR Collaboration},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.14604},
eprint = {2609.14604},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.14604},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Photon-induced J/ψ as a linearly polarized probe of collision geometry in relativistic heavy-ion collisions
AU - STAR Collaboration
PY - 2026
DA - 2026/09/13
PB - arXiv
DO - 10.48550/arxiv.2609.14604
UR - https://arxiv.org/abs/2609.14604
AB - In relativistic heavy-ion collisions, the linear polarization of quasi-real photons can correlate the spin orientation of photon-induced vector mesons with the collision geometry. To explore this sensitivity, we present the first measurement of the decay angular distribution of photon-induced J/ψ with respect to the event plane in heavy-ion collisions with hadronic overlap. The analysis uses Ru+Ru and Zr+Zr collisions at a nucleon--nucleon center-of-mass energy of √(s_NN)=200 GeV recorded by STAR. After correcting for the finite event-plane resolution and subtracting the residual hadronic contribution, we extract a negative second-order modulation, A_2^phot = −0.39 ± 0.11 (stat.) ± 0.04 (sys.), for |y^ee|<0.8, p_T^ee<0.2 GeV/c, and 30--80% centrality. This modulation provides evidence that the J/ψ polarization is correlated with the event plane, as expected for linearly polarized photons. The observed modulation establishes polarized J/ψ photoproduction as a direct probe of the transverse orientation of the initial collision geometry.
ER -