Dilepton azimuthal anisotropy from coherent $J/ψ$ photoproduction in hadronic Pb-Pb collisions
Hadron-based event-plane estimators can be affected by nonflow and autocorrelation biases, especially at low multiplicity. Coherent $J/ψ$ photoproduction offers a complementary geometry reference through the correlation between quasireal-photon polarization and the reaction plane. We calculate the second-order dilepton coefficient $A_2$ relative to the reaction plane in hadronic Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.36$ TeV within an equivalent-photon and generalized vector-meson-dominance Glauber framework. Nuclear diffraction and two-source interference produce a pronounced transverse-momentum dependence, while the rapidity dependence is weak. We also compare two treatments of coherent scattering in the overlap region of the two colliding nuclei. Suppressing the contribution from this region reduces the yield and strengthens the integrated polarization--reaction-plane correlation, with the largest differences in central and semicentral collisions and smaller differences toward peripheral collisions. Joint measurements of the coherent yield and $A_2$ can constrain how hadronic interactions disrupt nuclear coherence and clarify the photoproduction mechanism. With sufficient tagged yields, azimuthal correlations involving decay leptons from photoproduced $J/ψ$ mesons could complement studies of collectivity, with potential future applications to small systems.