Observation of the $\Upsilon \left(3S\right)$ Meson and Suppression of $\Upsilon $ States in Pb-Pb Collisions at $\sqrt{{s}_{NN}}=5.02\text{}\text{}\mathrm{TeV}$

The production of $\Upsilon \left(2S\right)$ and $\Upsilon \left(3S\right)$ mesons in lead-lead (Pb-Pb) and proton-proton ($pp$) collisions is studied in their dimuon decay channel using the CMS detector at the LHC. The $\Upsilon \left(3S\right)$ meson is observed for the first time in Pb-Pb collisions, with a significance above 5 standard deviations. The ratios of yields measured in Pb-Pb and $pp$ collisions are reported for both the $\Upsilon \left(2S\right)$ and $\Upsilon \left(3S\right)$ mesons, as functions of transverse momentum and Pb-Pb collision centrality. These ratios, when appropriately scaled, are significantly less than unity, indicating a suppression of $\Upsilon $ yields in Pb-Pb collisions. This suppression increases from peripheral to central Pb-Pb collisions. Furthermore, the suppression is stronger for $\Upsilon \left(3S\right)$ mesons compared to $\Upsilon \left(2S\right)$ mesons, extending the pattern of sequential suppression of quarkonium states in nuclear collisions previously seen for the $J/\psi $, $\psi \left(2S\right)$, $\Upsilon \left(1S\right)$, and $\Upsilon \left(2S\right)$ mesons.