Evidence of Nuclear Geometry-Driven Anisotropic Flow in O+O and Ne+Ne Collisions at sqrt[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 ^{16}O and ^{20}Ne 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 ^{16}O-^{16}O and ^{20}Ne-^{20}Ne collisions at a center-of-mass energy per nucleon pair of sqrt[s_{NN}]=5.36  TeV with the ALICE detector. The hydrodynamic model predictions, explicitly incorporating the nuclear structures of ^{16}O and ^{20}Ne, 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.