Upsilon production in PbPb collisions at LHC

The three $\Upsilon(1S, 2S, 3S)$ states can be separated using the CMS experimental apparatus via their dimuon decays in both pp and heavy-ion collisions. A suppression of the $\Upsilon(1S)$, $\Upsilon(2S)$ and $\Upsilon(3S)$ mesons is observed in PbPb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV, compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. Furthermore, a suppression of the excited $\Upsilon$ states has been measured with respect to the $\Upsilon$ ground state, expressed as a double ratio [$\Upsilon(nS)$/$\Upsilon(1S)$]$_{\text{PbPb}}$ / [$\Upsilon(nS)$/$\Upsilon(1S)$]$_{\text{pp}}$ with n = 2, 3, and 2 + 3. The centrality dependence of the double ratio, as well as the nuclear modification factors ($R_{\text{AA}}$) of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states are presented as a function of collision centrality, based on the analysis of the full data sample collected during the 2011 PbPb run, which corresponds to an integrated luminosity of 150 $\mu b^{-1}$.