Temporal and spatial structure of the extensive air shower front with the ARGO-YBJ experi- ment

Abstract

The ARGO-YBJ experiment is an Extensive Air Shower array currently operating at the high altitude Yang- bajing Cosmic Ray Laboratory (Tibet, P.R. China 4300 m a.s.l.). The detector consists of a dense layer of Resistive Plate Counters (RPCs) covering an area of about 6700 m 2 . One of the major benefits of having this design is the ability to measure the temporal and spatial structure of secondary par ticles of the shower with high time resolution and with an accurate determination of their position at the ground. Thi s provides a unique enviroment to explore cosmic ray showers with respect to their front shape. We present a detailed stud y of the curvature and of the thickness of the shower disc using events with energies up to several hundreds of TeV. Detailed Monte Carlo simulations of the shower development and of the detector response are performed to investigate the impl ications of our observations. Finally, we discuss the poten tial of this measurement in the evaluation of standard surface ar ray observables with particular attention to the events wit h time structure peculiarities like double shower fronts are discussed.