J/$\psi$ elliptic and triangular flow in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV

The ALICE collaboration
JHEP 10 (2020) 141, 2020.

Abstract (data abstract)
The inclusive J/$\psi$ elliptic ($v_2$) and triangular ($v_3$) flow coefficients are measured at forward rapidity (2.5 $<y<$ 4) and the $v_2$ at midrapidity ($|y|<$ 0.9) in Pb$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV using the ALICE detector at the LHC. The entire Pb$-$Pb data sample collected during Run 2 is employed, amounting to integrated luminosities of about 750 $\mu$b$^{-1}$ at forward rapidity and 93 $\mu$b$^{-1}$ at midrapidity. The results are obtained with the scalar product method and are reported as a function of transverse momentum $p_T$ and collision centrality. At forward rapidity, an ordering is observed for the $v_2$ and $v_3$ coefficients up to 5 GeV/$c$ when comparing pions, D mesons, and inclusive J/$\psi$. The midrapidity J/$\psi$ $v_2$ are in agreement with the forward rapidity results. At $p_T$ $>$ 5 GeV/$c$, the J/$\psi$ $v_2$ exhibits the same behavior as D mesons and pions. The J/$\psi$ $v_3$ in the 0$-$50% centrality interval is found to be positive for $2<p_T<5$ GeV/$c$ with a significance of 5.1$\sigma$ while the $v_3/v_2$ ratio is lower than the one observed for D mesons and light flavored particles. The ratio of $\pi^{\pm}$ $v_2$ over the $p_T$-integrated J/$\psi$ $v_2$ for $p_T$ $<$ 5 GeV/$c$ reveals an increasing trend from central to peripheral collisions. Using a simplistic extension of the quark scaling approach involving both light and charm quark flow components, it is shown that the D-meson $v_n$ measurements can be described based on those for charged pions and J/$\psi$ flow.

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