The shapes of the atmospheric Cherenkov light images from extensive air showers

Abstract

Experimental results on the shapes of atmospheric Cherenkov light images from Extensive Air Showers at E0 = 1013–1014 eV are presented. The results are based on data obtained by the first element of the Cherenkov light array of the EAS-TOP experiment at Campo Imperatore (2005 m a.s.l., National Gran Sasso Laboratories, Italy). Images are obtained with pixel field of view ω = 1.5 × 10−5 sr and full field of view Ω ≈ 10−3 sr. The shapes of the images agree with the expectations and their fluctuations are large and significant. Experimental data on the dependence of the image shapes on the detection geometry are reported. The images are well reproduced by two independent side by side detectors, within measured accuracies. Such accuracies (≈ 15% for large photoelectron content) define the level at which each pixel content is related to the shower structure. The presence of events characterized by patterns with multiple structures is proved. It is shown that such features are related to physical fluctuations of the shower structure.