Revealing Secondary Particle Signatures in PoCA-Based Muography

Abstract: This work reinterprets so-called 'noise' in cosmic ray imaging, demonstrating that reconstructed Points of Closest Approach (PoCA points) at the detector locations contain valuable physical information that has been traditionally disregarded. Through comprehensive analysis of data from the detection system of four resistive plate chambers (RPCs) and Monte Carlo simulations employing energy deposition weighting for coordinate determination, we establish that these points physically originate from secondary particles produced by cosmic ray interactions with materials of both detectors and surrounding structures. The research yields two principal findings: first, the generation of secondary particles significantly affects the measurement accuracy of cosmic ray positions; second, the roof structure significantly impacts the distribution of PoCA points at detector positions, where quantitative analysis demonstrates a strong correlation between roof thickness and the number of reconstructed PoCA points -- a relationship that can be precisely measured through z-coordinate distribution analysis in specific intervals. These discoveries demonstrate that the same detection system can extract information from a new dimension, enabling acquisition of more comprehensive physical results. More importantly, it suggests the necessity to revise standard analysis approaches to fully exploit this additional information channel in cosmic ray tomography.