Abstract
Atmospheric parameters, such as pressure ( P), temperature ( T) and density ( ρ ∝ P / T ) , affect the development of extensive air showers initiated by energetic cosmic rays. We have studied the impact of atmospheric variations on extensive air showers by means of the surface detector of the Pierre Auger Observatory. The rate of events shows a ∼ 10 % seasonal modulation and ∼ 2 % diurnal one. We find that the observed behaviour is explained by a model including the effects associated with the variations of P and ρ . The former affects the longitudinal development of air showers while the latter influences the Molière radius and hence the lateral distribution of the shower particles. The model is validated with full simulations of extensive air showers using atmospheric profiles measured at the site of the Pierre Auger Observatory.
Highlights
High-energy cosmic rays (CRs) are measured by recording the extensive air showers (EAS) of secondary particles they produce in the atmosphere
We have studied the atmospheric effects on EAS by means of the surface detector (SD) of the Pierre Auger Observatory, located in Malargüe, Argentina (35.2°S, 69.5°W) at 1400 m a.s.l. [1]
Assuming that the cosmic ray spectrum is a pure power law, i.e. dJ=dE0 / EÀ0 c, using Eq (7), and neglecting the small energy dependence of the weather coefficients, we find that dJ dS
Summary
High-energy cosmic rays (CRs) are measured by recording the extensive air showers (EAS) of secondary particles they produce in the atmosphere. We have studied the atmospheric effects on EAS by means of the surface detector (SD) of the Pierre Auger Observatory, located in Malargüe, Argentina (35.2°S, 69.5°W) at 1400 m a.s.l. The modulation is described by means of three coefficients that depend on the EAS zenith angle ðhÞ They are related to variations of P and q, measured at ground level, on slower (daily-averaged) and faster (within a day) time scales. 4, we perform full simulations of EAS developing in various realistic atmospheres (based on measurements from balloon soundings above the site of the Pierre Auger Observatory) in order to compare, in Section 5, the results from data and simulations with the predictions of the model. Model of atmospheric effects for the surface detector of the Auger Observatory
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