Trigger and Aperture of the Surface Detector Array of the Pierre Auger Observatory

摘要

The surface detector array of the Pierre Auger Observatory consists of 1600water-Cherenkov detectors, for the study of extensive air showers (EAS)generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy,from the identification of candidate showers at the level of a single detector,amongst a large background (mainly random single cosmic ray muons), up to theselection of real events and the rejection of random coincidences. Such triggermakes the surface detector array fully efficient for the detection of EAS withenergy above $3\times 10^{18}$ eV, for all zenith angles between 0$^\circ$ and60$^\circ$, independently of the position of the impact point and of the massof the primary particle. In these range of energies and angles, the exposure ofthe surface array can be determined purely on the basis of the geometricalacceptance.