Nucleus size dependence of charged-particle nuclear suppression with the CMS experiment

Collisions between atomic nuclei at extremely high energies can create a short-lived state of matter known as the quark-gluon plasma, where quarks and gluons move freely rather than being confined inside protons and neutrons. A key signature of this medium is that energetic particles lose energy as they traverse it, leading to a suppression of high-momentum particle yields relative to expectations based on proton-proton collisions scaled by the number of nucleon-nucleon interactions. While other properties of the quark-gluon plasma, such as collective, hydrodynamic-like flow, have been observed even in smaller systems like proton-nucleus collisions, clear evidence of parton energy loss in such systems remains elusive. In this talk, we present the first cross section measurements of high-momentum charged particles produced in oxygen-oxygen and neon-neon collisions at the Large Hadron Collider, using data recorded by the CMS experiment in 2025, as well as their ratio relative to a scaled proton-proton baseline spectrum. By comparing these results with those from larger systems, such as xenon-xenon and lead-lead collisions, we study how energy loss and other nuclear effects depend on the size of the colliding nuclei. These measurements provide new insight into the minimal conditions required for the emergence of a deconfined, collective state of quarks and gluons.