Evidence of Nuclear Geometry-Driven Anisotropic Flow in O + O and Ne + Ne Collisions at s NN = 5.36 TeV

A central question in strong-interaction physics, governed by quantum chromodynamics (QCD), is whether femtoscale droplets of quark-gluon plasma form in small collision systems involving projectiles significantly smaller than heavy ions. Collisions of light ions such as O 16 and Ne 20 offer a unique opportunity to probe the emergence of collective behavior in QCD matter. This Letter presents the first measurements of the elliptic ( v 2 ) and triangular ( v 3 ) flow of charged particles in O 16 – O 16 and Ne 20 – Ne 20 collisions at a center-of-mass energy per nucleon pair of s NN = 5.36 TeV with the ALICE detector. The hydrodynamic model predictions, explicitly incorporating the nuclear structures of O 16 and Ne 20 , exhibit a good agreement with the flow measurements presented. The observed increase of v 2 in central Ne–Ne collisions relative to OO collisions, driven by the nuclear geometries, highlights the importance of utilizing light nuclei with well-defined geometric shapes to constrain the initial conditions. These findings support the presence of nuclear geometry-driven hydrodynamic flow in light-ion collisions at the LHC.