Nuclear modification of Y states in PbPb

Yields of $\Upsilon$(1S), $\Upsilon$(2S) and $\Upsilon$(3S) mesons are measured in the CMS experiment via their $\mu^+ \mu^-$ decays, for bottomonium rapidity $|y|<2.4$, in PbPb and pp collisions at the same energy, $\sqrt{s_{\rm NN}} = 2.76$~TeV. The CMS detector was used to collect integrated luminosity of 166~$\mu$b$^{-1}$ for PbPb and 5.4~pb$^{-1}$ for pp, corresponding to a similar total number of nucleon-nucleon collisions. Differential cross sections and nuclear modification factors are reported as functions of rapidity and transverse momentum, as well as collision centrality, for the $\Upsilon$(1S) and the $\Upsilon$(2S). By comparing to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions, a strong, centrality-dependent suppression is observed in PbPb collisions, by up to a factor of 2 and 10, for the $\Upsilon$(1S) and the $\Upsilon$(2S), respectively. No significant dependences are observed as functions of rapidity or transverse momentum. The $\Upsilon$(3S) was not observed in PbPb collisions, being suppressed by more than 7 at the 95\% confidence level.