Study of the efficiency for the SD-433 array

G. SILLI; D. G. MELO; D. RAVIGNANI; N. GONZÁLEZ; D. SCHMIDT; A. ETCHEGOYEN

PUBLICACION INTERNA DE LA COLABORACION INTERNACIONAL AUGER

Pierre Auger Observatory

Año: 2021

2250-835X

The installation of the SD-433 array, proposed as a low-energy enhancement of thePierre Auger Observatory, started in November 2011 and achieved its current configurationin June 2019. The SD-433 array consists on 19 water cherenkov detectors placed at 433 m.Our motivation is to identify the energy threshold where the SD-433 array starts to befully efficient for extensive air showers initiated by proton and iron primaries. On thebase of what is presented in this note, the SD-433 array will be able to measure theenergy region where previous experiments have shown evidences for the second knee. Adataset of CORSIKA simulated air showers for iron and proton primaries reconstructedusing the Offline framework, is used to evaluate the reconstruction efficiency as a functionof the energy and zenith angle. Moreover, we investigated the impact of the new ToTdand MoPS trigger algorithms on the energy threshold. The results reveal a reduction inthe energy threshold when using the ToTd and MoPS trigger types lowering the SD-433full-efficiency energy threshold of one bin.The study outlines that the detector is more efficient for proton showers than iron andwe explain this outcome studying the attenuation of signals of air showers with increasingtransversed atmosphere. We present the first study on the SD-433 trigger efficiency described in dependence of the simulated energy and zenith angle which lead to the choiceof a zenith angle cut at 45 deg. The array becomes 97% efficient from 10**16.5eV and 10**16.6eVfor proton and iron primaries respectively up to a zenith angle of 45 deg.