The trigger system of the ARGO-YBJ experiment

ARGOL-YBJ is a ground-based γ and cosmic ray telescope presently under construction at the Yangbajing High Altitude Cosmic Ray Laboratory (4300 a.s.l.) nearby Lhasa (Tibet, People´s Republic of China). The apparatus has been designed to detect air showers with an energy threshold of a few hundreds GeV and it has a total active area of 6400m². The full-coverage central carpet of 5772 m² is equipped with an array of Resistive Plate Counters. This array is surrounded by a partially instrumented guard ring to improve the reconstruction of showers partially outside the detector´s core. The ARGO trigger logic implements simple yet robust algorithms, based on the timing distribution of the hits and their multiplicity on the central carper. In this paper, we describe the hardware architecture and the main features of the trigger system.