EMMI Workshop: Light-ion collisions 2026

Based on arXiv:2603.23596, we show that oxygen-oxygen (OO) collisions provide a unique arena for detecting rare, high momentum-transfer $2 \rightarrow 2$ Molière scatterings between energetic jet partons and quark- and gluon-like quasiparticles in quark-gluon plasma (QGP). In larger collision systems such as PbPb, jet substructure measurements are often dominated by a jet selection bias: jets that lose less energy are preferentially selected, and such jets tend to have narrower and harder internal structure. This selection bias obscures the genuine broadening induced by Molière scatterings. In OO collisions, the smaller size of QGP droplets reduces the amount of jet energy loss and suppresses this bias, allowing the effects of hard scattering of jet partons off QGP quasiparticles to dominate in select observables. We first show that Hybrid Model calculations agree with recent CMS charged-hadron $R_{\rm AA}$ data in OO collisions only when Molière scatterings are included. We then show that these scatterings broaden the Soft Drop angle $R_g$, enhancing the population of anti-$k_T$ jets with $R_g \gtrsim 0.2$ in OO collisions relative to pp collisions.

Energy-energy correlators (EECs) provide a complementary and especially revealing probe. In OO collisions, EECs exhibit enhanced large-angle correlations from jet-induced wakes and Molière scatterings; with suitable constituent-$p_T$ cuts, contributions to the EEC observable from soft jet-induced wakes can be suppressed, isolating the harder angular correlations generated by Molière scatterings. The resulting OO/pp EEC ratio develops a characteristic bump whose angular position reflects the typical angle of a Molière scattering. As the jet $p_T$ is increased, this bump shifts to smaller angles because a comparable transverse momentum kick from the medium produces a smaller angular deflection of a more energetic jet parton. Measuring both the existence of this bump and its systematic shift with jet $p_T$ in data would provide unambiguous, model-independent evidence that jet partons can resolve the microscopic quasiparticle structure of QGP.