J/Psi Elliptic Flow in Pb-Pb Collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV

ALICE Collaboration

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 $\sqrt{s_{\rm NN}} = 2.76$ 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 $0 < p_{\rm T} < 10$ GeV/$c$. For semi-central Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV, an indication of non-zero $v_2$ is observed with a maximum value of $v_2 = 0.116 \pm 0.046 {\rm (stat.)} \pm 0.029 {\rm (syst.)}$ for J/$\psi$ in the transverse momentum range $2 < p_{\rm T} < 4$ 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.

Figures

Figure 1

Invariant mass distribution (a) and $\langle \cos 2 (\phi - \Psi) \rangle$ as a function of $m_{\mu\mu}$ (b) of OS dimuons with $2 \leq p_{\rm T}< 4$ GeV/$c$ and $2.5 < y < 4$ in semi-central (20\%--40\%) Pb-Pb collisions.
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Figure 2

Inclusive J/$\psi$ $v_2$ vs $\pt$ for semi-central (20%-40%) Pb-Pb collisions at $\snn=2.76$ TeV (see text for details on uncertainties). The used $\pt$ ranges are: 0-2, 2-4, 4-6 and 6-10 GeV/$c$.
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Figure 3

$v_2$ (a) and $\langle p_{\rm T} \rangle^{\rm uncor}$ (b) of inclusive J/$\psi$ with $1.5 \leq p_{\rm T} < 10$ GeV/$c$ as a function of $\langle N_{\rm{part}} \rangle$ in Pb-Pb collisions at $\snn=2.76$ TeV (see text for details on uncertainties).
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Figure 4

Inclusive J/$\psi$ $v_2$ vs $\pt$ for non-central (20%-60%) Pb-Pb collisions at $\snn=2.76$ TeV (see text for details on uncertainties). The used $\pt$ ranges are: 0-2, 2-4, 4-6 and 6-10 GeV/$c$. Calculations from two transport models are also shown (see text for details).
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