Evolution of first-interaction second-harmonic anisotropy in cosmic-ray air showers
Abstract
The longitudinal evolution of second-harmonic anisotropy inherited from the first interaction in extensive air showers is investigated with CORSIKA simulations. Events with large initial anisotropy are selected. Second-harmonic observables are evaluated separately using the coordinate and momentum azimuths at several atmospheric depths and compared with their corresponding initial harmonic orientations. More than 84% of the initial second-harmonic signal is attenuated within the first 20 g cm−2 of shower development. In coordinate space, the second-harmonic correlation with the initial orientation persists to ground level at approximately 0.09% of its initial magnitude. This residual is evaluated against a matched source-isotropized reference, constructed for each selected event by independently randomizing the azimuths of the first-interaction final-state particles and simulating the shower under identical atmospheric conditions. The positive coordinate-space ensemble-mean difference at ground level is statistically resolved, and the two samples show little event-level separation. In momentum space, a weak ensemble-level residual remains at 200 g cm−2, and the original and source-isotropized signals become statistically indistinguishable by 300 g cm−2 and remain so at ground level.
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BibTeX
@misc{sun2026evolution,
title = {{Evolution of first-interaction second-harmonic anisotropy in cosmic-ray air showers}},
author = {Hao Sun and Cunfeng Feng},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.12380},
eprint = {2609.12380},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.12380},
}
RIS
TY - UNPB
TI - Evolution of first-interaction second-harmonic anisotropy in cosmic-ray air showers
AU - Hao Sun
AU - Cunfeng Feng
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2609.12380
UR - https://arxiv.org/abs/2609.12380
AB - The longitudinal evolution of second-harmonic anisotropy inherited from the first interaction in extensive air showers is investigated with CORSIKA simulations. Events with large initial anisotropy are selected. Second-harmonic observables are evaluated separately using the coordinate and momentum azimuths at several atmospheric depths and compared with their corresponding initial harmonic orientations. More than 84% of the initial second-harmonic signal is attenuated within the first 20 g cm^−2 of shower development. In coordinate space, the second-harmonic correlation with the initial orientation persists to ground level at approximately 0.09% of its initial magnitude. This residual is evaluated against a matched source-isotropized reference, constructed for each selected event by independently randomizing the azimuths of the first-interaction final-state particles and simulating the shower under identical atmospheric conditions. The positive coordinate-space ensemble-mean difference at ground level is statistically resolved, and the two samples show little event-level separation. In momentum space, a weak ensemble-level residual remains at 200 g cm^−2, and the original and source-isotropized signals become statistically indistinguishable by 300 g cm^−2 and remain so at ground level.
ER -