EMMI Workshop: Light-ion collisions 2026

We study the bulk collective behaviour in ion collision systems, going from PbPb to light ions, in the context of the Relativistic Boltzmann Transport model. This kinetic theory approach numerically solves the Boltzmann Equation with the full collision integral, including realistic event-by-event initial conditions, a non-conformal equation of state and $\eta/s(T)$. The model is suitable to describe the light sector in smaller collision systems, such as $^{16}$O and $^{20}$Ne, being able to cope with far-from-equilibrium regions which are expected to be more relevant than in the heavy-ion case. We investigate the dependence of the collective flows and of the collective response on the centrality classes, focusing in particular on the most central collisions, in which the imprints of the nuclear structure are known to be stronger. Moreover, we look for universality in the response functions $v_n/\varepsilon_n$ vs Knudsen number, aiming at identifying the transition from the hydrodynamic to the particle-like regime. Finally, we explore the dependence of the observables on the temperature-dependence of $\eta/s(T)$, especially in the region across the critical temperature.