Observation of sequential $\Upsilon$ suppression in PbPb collisions

The sequential suppression of the individual $\Upsilon$ states in PbPb collisions with respect to their yields in $pp$ data has been measured. The PbPb and $pp$ datasets used in these proceedings correspond to integrated luminosities of 150/$\mu$b and 230/nb, respectively, collected by the CMS experiment at the LHC at 2.76 TeV in 2011. The relative suppression of the excited $\Upsilon$ states has been measured with respect to the $\Upsilon$(1S) ground state, expressed as a double ratio [$\Upsilon$(nS)/$\Upsilon$(1S)]$_{PbPb}$ /[$\Upsilon$(nS)/$\Upsilon$(1S)]$_{pp}$. The absolute suppression of the $\Upsilon$(nS) yields in PbPb relative to the yields in $pp$ scaled by the number of nucleon-nucleon collisions, $R_{AA}$, is measured as a function of the collision centrality. Integrated over centrality, the $R_{AA}$ values for $\Upsilon$(1S), $\Upsilon$(2S), and the upper limit of $\Upsilon$(3S) $R_{AA}$ are reported in these proceedings, which demonstrate the sequential suppression of the $\Upsilon$(nS) states in PbPb collisions at LHC energies.