Measurement of the $\psi$(2S) meson in PbPb collisions at $\sqrt{s_{_{NN}}}$ = 2.76 TeV

This document presents the measurements of inclusive $\psi$(2S)$\rightarrow\mu\mu$ decays relative to $J/\psi\rightarrow\mu\mu$ in PbPb and pp collisions at $\sqrt{s_{_{NN}}} = 2.76$~TeV. The analysis is based on a data sample collected during the PbPb run in 2011, which corresponds to an integrated luminosity of $150\mu b^{-1}$ , and a sample of pp data with an integrated luminosity of $231 nb^{-1}$. In three event centrality ranges, the double ratio of measured yields $(N_{\psi(2S)} / N_{J/\psi})_{PbPb}/(N_{\psi(2S)} / N_{J/\psi})_{pp}$ is computed, for two kinematical domains: lower $p_T$ ($p_T>3.0$~GeV/c) at forward rapidity ($1.6<|y|<2.4$), and higher $p_T$ ($p_T>6.5$~GeV/c) at mid-rapidity ($|y|<1.6$). The value of this double ratio in the lower-$p_T$ region and for the most central collisions is 5.32$\pm$1.03~(stat.)~$\pm$~0.79~(syst.)~$\pm$~2.58~(pp).