Search for collectivity with azimuthal J/ψ-hadron correlations in high multiplicity p–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ and 8.16 TeV

Abstract

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 ${\mu }^{+}{\mu }^{-}$ decay channel, while the charged hadrons are reconstructed at mid-rapidity ($|\eta |<1.8$). 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 $\mathrm{\Delta }\phi \approx 0$ and $\mathrm{\Delta }\phi \approx \pi$, 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 5σ. The obtained results are similar to the J/ψ $v_2$ coefficients measured in Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, suggesting a common mechanism at the origin of the J/ψ $v_2$.