Evidence for sequential (nS) suppression in light ion collisions
arXiv:2607.13758
The CMS Collaboration measured the production of the three lowest‑mass bottomonium states (Υ(1S), Υ(2S), Υ(3S)) in oxygen‑oxygen and neon‑neon collisions at √sₙₙ = 5.36 TeV and found that the excited states are more strongly suppressed than the ground state, providing evidence for sequential quark‑gluon plasma suppression in light‑ion collisions.
Abstract
Bound states of heavy quark-antiquark pairs, known as quarkonia, have long been regarded as particularly sensitive probes of the quark-gluon plasma (QGP). Comparing quarkonium yields in collisions of heavy nuclei, such as gold or lead, with a proton-proton (pp) reference reveals a characteristic pattern of sequential suppression, in which weakly-bound excited states are more strongly suppressed than the ground states. We report the first measurements of the three lowest mass -wave vector bottomonium resonances, the ground state (1S) and the excited states (2S) and (3S), in oxygen-oxygen collisions at a center-of-mass energy per nucleon pair of = 5.36 TeV. Measurements of the yields of the (1S) and (2S) resonances in neon-neon collisions, at the same , are also presented. The (2S)/(1S) ratio is found to be significantly below the measured pp reference value, and the (3S)/(1S) ratio shows an even larger reduction. The significance of the relative (3S) to (2S) suppression exceeds three standard deviations. These results provide evidence for the sequential suppression of (nS) states in light ion collisions, similar to observations made in lead-lead and gold-gold collisions, generally attributed to the presence of a QGP medium.
Submitted to Physical Review Letters. All figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIN-25-015 (CMS Public Pages)