EMMI Workshop: Light-ion collisions 2026

One of the most unanticipated findings of the LHC heavy ion program is the observation of stronger suppressions of the excited $\Upsilon$ states compared to the lower $\Upsilon\mathrm{(1S)}$~state in \mbox{proton-lead} collisions, with the same hierarchy as seen in the larger \mbox{lead-lead}~(PbPb) collision events. Together with other observations of signatures of quark-gluon plasma formation in ``small systems'', this feature raises the question of whether a hot medium can be produced in such systems and motivates studies for ions with different sizes. We report the first measurement of $\Upsilon$~mesons in \mbox{oxygen-oxygen} and \mbox{neon-neon} collisions and the observation of stronger suppression for the excited states. The yield ratios relative to the $\Upsilon\mathrm{(1S)}$ production rate are compared with similar results from other collision systems as well as with models describing the nuclear modification of quarkonium production in (deconfined) media.