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| 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) ; | ||
| Figures | |
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Figure 1:
Dimuon invariant-mass distributions in the pp reference sample, $ \text{OO} $, and $ \text{NeNe} $ collisions, from left to right. The overlaid curves show the corresponding fit results, integrated over muon-pair $ p_{\mathrm{T}} < 30 $ GeV and $ |y| < $ 2.4. In each case, the total fit model is shown as a solid line, while the individual $ \Upsilon $meson signal components and the background are shown as dashed lines. |
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Figure 2:
System-size dependence of the $ \Upsilon $meson ratios. Left: double ratios $ \Upsilon{\textrm{(2S)}} $/$ \Upsilon{\textrm{(1S)}} $ and $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(1S)}} $ as a function of $ \langle N_{\text{part}}\rangle $, compared with previous $ \mathrm{p}\text{Pb} $ [38] and PbPb [33,34,31,32] measurements at the LHC. Right: single ratios as a function of $ N_{\text{trk}}^{\text{corr}} $, compared with pp [63] and PbPb [31,32] measurements at the LHC. Predictions obtained with the SHINCHON framework [64] are overlaid. |
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Figure 2-a:
System-size dependence of the $ \Upsilon $meson ratios. Left: double ratios $ \Upsilon{\textrm{(2S)}} $/$ \Upsilon{\textrm{(1S)}} $ and $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(1S)}} $ as a function of $ \langle N_{\text{part}}\rangle $, compared with previous $ \mathrm{p}\text{Pb} $ [38] and PbPb [33,34,31,32] measurements at the LHC. Right: single ratios as a function of $ N_{\text{trk}}^{\text{corr}} $, compared with pp [63] and PbPb [31,32] measurements at the LHC. Predictions obtained with the SHINCHON framework [64] are overlaid. |
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Figure 2-b:
System-size dependence of the $ \Upsilon $meson ratios. Left: double ratios $ \Upsilon{\textrm{(2S)}} $/$ \Upsilon{\textrm{(1S)}} $ and $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(1S)}} $ as a function of $ \langle N_{\text{part}}\rangle $, compared with previous $ \mathrm{p}\text{Pb} $ [38] and PbPb [33,34,31,32] measurements at the LHC. Right: single ratios as a function of $ N_{\text{trk}}^{\text{corr}} $, compared with pp [63] and PbPb [31,32] measurements at the LHC. Predictions obtained with the SHINCHON framework [64] are overlaid. |
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Figure 3:
Sequential suppression of bottomonium across collision systems. Left: measured $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(1S)}} $ and $ \Upsilon{\textrm{(2S)}} $/$ \Upsilon{\textrm{(1S)}} $ double ratios for $ \mathrm{p}\text{Pb} $, $ \text{OO} $, $ \text{NeNe} $, and PbPb collisions. Right: $ p_{\mathrm{T}} $-differential $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(2S)}} $\ double ratio in $ \text{OO} $ and PbPb collisions, together with the SHINCHON prediction for $ \text{OO} $ [64]. |
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Figure 3-a:
Sequential suppression of bottomonium across collision systems. Left: measured $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(1S)}} $ and $ \Upsilon{\textrm{(2S)}} $/$ \Upsilon{\textrm{(1S)}} $ double ratios for $ \mathrm{p}\text{Pb} $, $ \text{OO} $, $ \text{NeNe} $, and PbPb collisions. Right: $ p_{\mathrm{T}} $-differential $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(2S)}} $\ double ratio in $ \text{OO} $ and PbPb collisions, together with the SHINCHON prediction for $ \text{OO} $ [64]. |
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Figure 3-b:
Sequential suppression of bottomonium across collision systems. Left: measured $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(1S)}} $ and $ \Upsilon{\textrm{(2S)}} $/$ \Upsilon{\textrm{(1S)}} $ double ratios for $ \mathrm{p}\text{Pb} $, $ \text{OO} $, $ \text{NeNe} $, and PbPb collisions. Right: $ p_{\mathrm{T}} $-differential $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(2S)}} $\ double ratio in $ \text{OO} $ and PbPb collisions, together with the SHINCHON prediction for $ \text{OO} $ [64]. |
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Figure 4:
Double ratios of $ \Upsilon{\textrm{(2S)}} $/$ \Upsilon{\textrm{(1S)}} $ and $ \Upsilon{\textrm{(3S)}} $/$ \Upsilon{\textrm{(1S)}} $ as a function of the muon-pair transverse momentum. The shaded boxes show systematic uncertainties, while the vertical bars indicate statistical ones. |
| Tables | |
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Table 1:
Summary of systematic uncertainty source ranges (in %) for the measured $ \Upsilon $meson ratios in $ \text{OO} $ and $ \text{NeNe} $ collisions. |
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Table 2:
Measured double ratios of excited-to-ground-state $ \Upsilon $meson yields in $ \text{OO} $ and $ \text{NeNe} $ collisions with dimuon $ p_{\mathrm{T}} < $ 30 GeV and $ |y| < $ 2.4. The first (second) uncertainty is statistical (systematic). |
| Summary |
| Measurements of the $ \Upsilon{\textrm{(1S)}} $, $ \Upsilon{\textrm{(2S)}} $, and $ \Upsilon{\textrm{(3S)}} $\ meson states are presented for the first time in oxygen-oxygen and neon-neon collisions, recorded in 2025 with the CMS detector at the CERN LHC at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.36 TeV. The suppression of excited states relative to the ground state is quantified using double ratios of excited-to-ground-state $ \Upsilon $meson yields in ion-ion collisions relative to proton-proton collisions at the same center-of-mass energy. The measured double ratios are below unity in $ \text{OO} $ and $ \text{NeNe} $ collisions, and a sequential suppression pattern is observed, with the more weakly bound excited states more strongly suppressed than the ground state. |
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