Investigation of Anisotropic Flow Signatures in Extensive Air Showers at Different Observation Heights

Anisotropic flow is a key observable for studying the quark–gluon plasma (QGP) in heavy-ion collisions. Similar collective phenomena may emerge in ultra-high-energy cosmic-ray (UHECR) interactions in the atmosphere. We investigate whether elliptic flow information (𝑣2) originating near the first interaction can survive down to lower altitudes of extensive air showers (EAS). Using CORSIKA (v77410) with EPOS-LHC for 100PeV Ne+N vertical showers, a fixed first-interaction height, and three observation levels, we reconstruct the second-harmonic event-plane angle Ψ2 and 𝑣2 via the𝑄-vector methodandcheck—qualitatively—whetherthese observables retain information at lower altitudes. We find that clear Ψ2 correlations persist at intermediate altitude (∼12km), while both correlation and 𝑣2 indications diminish closer to a ground-like level (∼4.4km). These results suggest a possible window for probing collective behavior in air showers with future analysis techniques and detector designs.