Study of J/ψ azimuthal anisotropy at forward rapidity in Pb-Pb collisions at √sNN=5.02 TeV

The second (v₂) and third (v₃) flow harmonic coefficients of J/ψ mesons are measured at forward rapidity (2.5 < y < 4.0) in Pb-Pb collisions at sNN=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 v₃ is observed with 3.7σ significance. The measurements, compared to those of prompt D⁰ mesons and charged particles at mid-rapidity, indicate an ordering with v_n(J/ψ) < v_n(D⁰) < v_n(h^±) (n = 2, 3) at low and intermediate p_T up to 6 GeV/c and a convergence with v₂(J/ψ) ≈ v₂(D⁰) ≈ v₂(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 v₃/v₂ 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 D⁰-meson ratio in the same p_T interval suggests an ordering similar to that of the v₂ and v₃ coefficients. The J/ψ v₂ 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.