EMMI Workshop: Light-ion collisions 2026

Light ion collisions at the LHC provide a unique opportunity to test the emergence of QGP-like collectivity in systems that are small in transverse size but highly sensitive to nuclear structure. Recent O+O and Ne+Ne measurements have established sizable anisotropic flow and a characteristic enhancement of elliptic flow in central Ne+Ne collisions, suggesting a hydrodynamic response to the intrinsic geometry of ${}^{20}$Ne. However, this interpretation is largely based on midrapidity observables and implicitly assumes that the observed collective response is representative of the light-ion fireball as a whole. Here we test this assumption by performing event-by-event simulations of ${}^{16}$O+${}^{16}$O, and ${}^{20}$Ne+${}^{20}$Ne collisions at $\sqrt{s_{\rm NN}}=5.36$ TeV with the 3D initial-state model McDIPPER coupled to the viscous hydrodynamic model CLVisc, followed by hadronic afterburner SMASH. The McDIPPER framework combines a $k_\perp$-factorized Color Glass Condensate hybrid approach with ab initio nuclear configurations, allowing us to follow how nuclear geometry are encoded in the longitudinal structure of the final state. By studying rapidity-dependent particle production, anisotropic flow, mean transverse momentum, and flow decorrelations, we characterize the longitudinal structure of collective dynamics in O+O and Ne+Ne collisions and provide a broader baseline for interpreting light-ion collisions beyond midrapidity.