Simulation of the ARGO-YBJ experiment operated in Scaler Mode

The ARGO-YBJ experiment is a large area full coverage detector operating at high mountain altitude (4300 m a.s.l., Tibet, China, ∼6700 m2 active surface). In scaler mode, the particle rate is recorded at fixed time intervals (0.5 s), allowing the achievement of an energy threshold as low as E t h ∼ 1 GeV for the photons. This result, together with the estimate of the effective area as a function of the primary energy, has been obtained using the simulation code CORSIKA6201 for the shower development in the atmosphere and a dedicated and detailed detector simulation, ARGOG, based on GEANT3.21. With this simulation chain, and using the known primary proton and helium spectra, we obtained counting rates consistent with the measured ones, making us confident in the expectation of the detector performance as far as the photon shower detection is concerned, which is of crucial importance to determine the capability of the ARGO-YBJ experiment to detect gamma-ray bursts (GRBs).