Evidence of Nuclear Geometry-Driven Anisotropic Flow in O+ O and Ne+Ne Collisions at sNN =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 O16 and Ne20 offer a unique opportunity to probe the emergence of collective behavior in QCD matter. This Letter presents the first measurements of the elliptic (v2) and triangular (v3) flow of charged particles in O16-O16 and Ne20-Ne20 collisions at a center-of-mass energy per nucleon pair of sNN=5.36 TeV with the ALICE detector. The hydrodynamic model predictions, explicitly incorporating the nuclear structures of O16 and Ne20, exhibit a good agreement with the flow measurements presented. The observed increase of v2 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.