Observation and research on cosmic ray muons and solar modulation effect based on plastic scintillator detector

Cosmic rays, originating from stars, supernovae, and other astrophysical sources, are composed of high-energy particles that enter Earth’s atmosphere. Upon interaction with atmospheric nuclei, these primary cosmic rays generate secondary particles, including neutrons, electrons, and muons, with muons constituting a dominant component at ground level. Muons, due to their relative abundance, stability, and well-characterized energy loss mechanisms, serve as critical probes for investigating the fundamental properties of cosmic rays. Studies of muon energy distribution, diurnal anisotropy, and their modulation by solar activity provide critical insights into the mechanism of particle acceleration in cosmic ray sources and the effects of solar and atmospheric.This study aims to characterize the counting spectra and anisotropic properties of cosmic ray muons by using a plastic scintillator detector system. The experiment was conducted over a three-month period, from December 2023 to February 2024, leveraging long-bar plastic scintillator detectors equipped with dual-end photomultiplier tubes (PMTs) and a high-resolution digital data acquisition system. A dual-end coincidence measurement technique was used to enhance the signal-to-noise ratio by suppressing thermal noise and other background interferences. Comprehensive calibration of the detection system was performed using standard gamma-ray sources, including <sup>137</sup>Cs, <sup>60</sup>Co, and <sup>40</sup>K, thereby ensuring precise energy scaling and reliable performance.The observed energy spectra of cosmic ray muons are in excellent agreement with theoretical predictions, which explains the energy losses caused by muons passing through the detector. Diurnal variations in muon count rates exhibit a pronounced pattern, with a systematic reduction occurring between 8:00 AM and 1:00 PM. This phenomenon is attributed to the solar shielding effects, where enhanced solar activity during daytime hours modulates the flux of galactic cosmic rays reaching Earth’s surface. To account for atmospheric influences, meteorological corrections are performed using temperature and pressure adjustment functions derived from regression analysis. These corrections indicate that atmospheric pressure and temperature are significant factors affecting muon count rates, and a clear linear relationship is observed.The study further corroborates these findings through cross-comparisons with data from the Yangbajing Cosmic Ray Observatory. Minor discrepancies, primarily in low-energy muon count rates, are attributed to variations in detector sensitivities and local atmospheric conditions. These observations underscore the robustness of the plastic scintillator detector system for capturing detailed muon spectra and anisotropic patterns.This research establishes a reliable experimental framework for analyzing cosmic ray muons and their modulation by solar and atmospheric phenomena. The results contribute to a more in-depth understanding of anisotropy of cosmic rays and the interaction between astrophysical and geophysical processes. Furthermore, these findings provide valuable insights for optimizing detection technologies and enhancing the accuracy of cosmic ray studies.