Analysis of annual periodicities in the muon rate measured by the EEE detectors installed at the high-latitude site of Ny-Ålesund

Three scintillator detectors with SiPM readout systems and low-cost control electronics have been deployed at the Ny Ålesund research station (Svalbard, 79°N) since 2019 to measure secondary cosmic ray muon flux. The detectors operate within the EEE Project network comprising approximately 100 Italian secondary schools. Analysis of the accumulated dataset spanning nearly five years reveals a pronounced periodic modulation in the muon count rate with an annual period. The Lomb-Scargle periodogram method, which uses sinusoidal fit optimization, was applied to quantify the amplitude and phase of this annual variation. The observed modulation was verified to be independent of environmental parameters and instrumental effects.