Search for collectivity with azimuthal J/ ψ-hadron correlations in high multiplicity p–Pb collisions at s NN = 5.02 and 8.16 TeV

摘要

We present a measurement of azimuthal correlations between inclusive J/ ψ and charged hadrons in p–Pb collisions recorded with the ALICE detector at the CERN LHC. The J/ ψ are reconstructed at forward (p-going, 2.03 < y < 3.53 ) and backward (Pb-going, ? 4.46 < y < ? 2.96 ) rapidity via their μ + μ ? decay channel, while the charged hadrons are reconstructed at mid-rapidity ( | η | < 1.8 ). The correlations are expressed in terms of associated charged-hadron yields per J/ ψ trigger. A rapidity gap of at least 1.5 units is required between the trigger J/ ψ and the associated charged hadrons. Possible correlations due to collective effects are assessed by subtracting the associated per-trigger yields in the low-multiplicity collisions from those in the high-multiplicity collisions. After the subtraction, we observe a strong indication of remaining symmetric structures at Δ φ ≈ 0 and Δ φ ≈ π , similar to those previously found in two-particle correlations at middle and forward rapidity. The corresponding second-order Fourier coefficient ( v 2 ) in the transverse momentum interval between 3 and 6 GeV/ c is found to be positive with a significance of about 5 σ . The obtained results are similar to the J/ ψ v 2 coefficients measured in Pb–Pb collisions at s NN = 5.02 TeV, suggesting a common mechanism at the origin of the J/ ψ v 2 .