Response of the Pierre Auger Observatory Water Cherenkov Detectors to Muons

Two test detectors similar to the Pierre Auger Observatory Water Cherenkov Detectors have been installed at the Observatory site and at the Institut de Physique Nucléaire d’Orsay. The signals from the tanks are read out using three 9” photomultipliers and analyzed by both a digital oscilloscope with high sampling frequency and the Auger surface detector electronics. Additionally, the detectors are equipped with plastic scintillators serving as muon telescopes. The trigger is provided either by the muon telescope or by the coincidence of the three PMTs. The scintillators are movable allowing the study of the detector response to atmospheric muons arriving with different incident angles. In this paper, the results of measurements for vertical and inclined background muons are presented. These results are compared to simulations and important calibration parameters are extracted. The influence of the direct light detected by the PMTs, particularly important for inclined showers, is discussed.