Trigger and aperture of the surface detector array of the Pierre Auger Observatory Pierre Auger Collaboration Bueno Villar, Antonio García Gámez, Diego González, J. G. Lozano Bahílo, Julio Navarro, J. L. Navas Concha, Sergio Ultra-high energy cosmic rays Pierre Auger Observatory Extensive air showers Trigger Exposure The surface detector array of the Pierre Auger Observatory consists of 1600 water-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 the selection of real events and the rejection of random coincidences. Such trigger makes the surface detector array fully efficient for the detection of EAS with energy above 3×1018 eV, for all zenith angles between 0∘ and 60∘, independently of the position of the impact point and of the mass of the primary particle. In these range of energies and angles, the exposure of the surface array can be determined purely on the basis of the geometrical acceptance. 2013-11-11T13:12:24Z 2013-11-11T13:12:24Z 2011 info:eu-repo/semantics/preprint Pierre Auger Collaboration. Trigger and aperture of the surface detector array of the Pierre Auger Observatory. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 613(1): 29-39 (2010). [http://hdl.handle.net/10481/29093] 0168-9002 arXiv:1111.6764v1 http://hdl.handle.net/10481/29093 doi: 10.1016/j.nima.2009.11.018 eng info:eu-repo/grantAgreement/EC/FP7/220240 http://creativecommons.org/licenses/by-nc-nd/3.0/ info:eu-repo/semantics/openAccess Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License Elsevier