CMS-PAS-HIN-25-015

CMS-PAS-HIN-25-015
Evidence for sequential $ \Upsilon $ meson suppression in light ion collisions
CMS Collaboration
2026-04-17

Abstract: Measurements of the three lowest $ S $-wave bottomonium resonances, $ \Upsilon(1\mathrm{S}) $, $ \Upsilon(2\mathrm{S}) $, and $ \Upsilon(3\mathrm{S}) $, are presented using data from oxygen-oxygen and neon-neon collisions recorded in 2025 by the CMS detector at the CERN LHC. The data correspond to a nucleon-nucleon center-of-mass energy of $ \sqrt{s_{\mathrm{NN}}}= $ 5.36 TeV and integrated luminosities of 8.4 $ \mathrm{nb}^{-1} $ (oxygen-oxygen) and 0.8 $ \mathrm{nb}^{-1} $ (neon-neon), with a proton-proton reference sample of 456 $ \mathrm{pb}^{-1} $ collected at the same energy. The suppression of the excited states relative to the ground state is quantified using double ratios of excited-to-ground-state $ \Upsilon $ yields in ion-ion collisions relative to those in proton-proton collisions. The measured double ratios in oxygen-oxygen collisions are 0.664 $ \pm $ 0.055 $ \mathrm{(stat)} \pm 0.007 \mathrm{(syst)} $ for $ \Upsilon(2\mathrm{S})/\Upsilon(1\mathrm{S}) $, 0.392 $ \pm $ 0.077 $ \mathrm{(stat)} \pm 0.023 \mathrm{(syst)} $ for $ \Upsilon(3\mathrm{S})/\Upsilon(1\mathrm{S}) $, and 0.59 $ \pm $ 0.12 $ \mathrm{(stat)} \pm 0.04 \mathrm{(syst)} $ for $ \Upsilon(3\mathrm{S})/\Upsilon(2\mathrm{S}) $. In neon-neon collisions, the $ \Upsilon(2\mathrm{S})/\Upsilon(1\mathrm{S}) $ double ratio is 0.271 $ \pm $ 0.117 $ \mathrm{(stat)} \pm 0.008 \mathrm{(syst)} $. All measurements are below unity, and a sequential suppression pattern is observed, with the more weakly bound states more strongly suppressed.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRL. The superseded preliminary plots can be found here.

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