Study of J/ψ azimuthal anisotropy at forward rapidity in Pb-Pb collisions at \( \sqrt{s_{\mathrm{NN}}}=5.02 \) TeV

The second (v$_{2}$) and third (v$_{3}$) flow harmonic coefficients of J/ψ mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}=5.02 $ TeV with the ALICE detector at the LHC. Results are obtained with the scalar product method and reported as a function of transverse momentum, p$_{T}$, for various collision centralities. A positive value of J/ψ v$_{3}$ is observed with 3.7σ significance. The measurements, compared to those of prompt D$^{0}$ mesons and charged particles at mid-rapidity, indicate an ordering with v$_{n}$(J/ψ) < v$_{n}$(D$^{0}$) < v$_{n}$(h$^{±}$) (n = 2, 3) at low and intermediate p$_{T}$ up to 6 GeV/c and a convergence with v$_{2}$(J/ψ) ≈ v$_{2}$(D$^{0}$) ≈ v$_{2}$(h$^{±}$) at high p$_{T}$ above 6–8 GeV/c. In semi-central collisions (5–40% and 10–50% centrality intervals) at intermediate p$_{T}$ between 2 and 6 GeV/c, the ratio v$_{3}$/v$_{2}$ of J/ψ mesons is found to be significantly lower (4.6σ) with respect to that of charged particles. In addition, the comparison to the prompt D$^{0}$-meson ratio in the same p$_{T}$ interval suggests an ordering similar to that of the v$_{2}$ and v$_{3}$ coefficients. The J/ψ v$_{2}$ coefficient is further studied using the Event Shape Engineering technique. The obtained results are found to be compatible with the expected variations of the eccentricity of the initial-state geometry.