$J/\psi$ Suppression at Forward Rapidity in Pb-Pb Collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$

The ALICE experiment has measured the inclusive $J/\psi$ production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ down to zero transverse momentum in the rapidity range $2.5<y<4$. A suppression of the inclusive $J/\psi$ yield in Pb-Pb is observed with respect to the one measured in $pp$ collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0%–80% most central collisions, is $0.545\pm 0.032(\mathrm{stat})\pm 0.083(\mathrm{syst})$ and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including $J/\psi$ production from charm quarks in a deconfined partonic phase can describe our data.

Figure 1

Invariant mass spectrum of ${\mu }^{+}{\mu }^{-}$ pairs (solid black circles) with $p_t\ge 0$ and $2.5<y<4$ in the 0%–80% most central Pb-Pb collisions.

Figure 2

Inclusive $J/\psi$ $R_{AA}$ as a function of the midrapidity charged-particle density (left) and the number of participating nucleons (right) measured in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ compared to PHENIX results in Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ at midrapidity and forward rapidity [4, 5, 23]. The ALICE data points are placed at the $d{N}_{\mathrm{ch}}^w/d\eta {|}_{\eta =0}$ and $⟨N_{\mathrm{part}}^w⟩$ values defined in Table 1.

Figure 3

Centrality integrated inclusive $J/\psi$ $R_{AA}$ measured in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ as a function of rapidity for two $p_t$ ranges. The open boxes contain the total systematic uncertainties except the ones on the integrated luminosity in the $pp$ reference and on the $T_{AA}$, i.e., 5.2% (8.3%) for the ALICE (CMS [11]) data. The two models [26, 27] predict the $R_{AA}$ due only to shadowing effects for nDSg (shaded areas) and EPS09 (lines) nPDF, respectively.

Figure 4

Inclusive $J/\psi$ $R_{AA}$ measured in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$ compared to the predictions by Statistical Hadronization model [29], Transport model I [30] and II [31], see text for details. The ALICE data points are placed at the $⟨N_{\mathrm{part}}^w⟩$ values defined in Table 1.