We report on the first measurement of inclusive $J/\psi$ elliptic flow $v_2$ in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$ in the rapidity range $2.5<y<4.0$. The dependence of the $J/\psi$ $v_2$ on the collision centrality and on the $J/\psi$ transverse momentum is studied in the range $0\le p_T<10\mathrm{GeV}/c$. For semicentral Pb-Pb collisions at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$, an indication of nonzero $v_2$ is observed with a largest measured value of $v_2=0.116\pm 0.046(\mathrm{stat})\pm 0.029(\mathrm{syst})$ for $J/\psi$ in the transverse momentum range $2\le p_T<4\mathrm{GeV}/c$. The elliptic flow measurement complements the previously reported ALICE results on the inclusive $J/\psi$ nuclear modification factor and favors the scenario of a significant fraction of $J/\psi$ production from charm quarks in a deconfined partonic phase.

• Received 24 March 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.162301

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© 2013 CERN, for the ALICE Collaboration