The accuracy of signal measurement with the water-Cherenkov detectors of the Pierre Auger Observatory

The Auger Surface Detector consists of a large array of water Cherenkov detector tanks each with a volume of 12,000 liters, for the detection of high energy cosmic rays. The accuracy in the measurement of the integrated signal amplitude of the detector unit has been studied using experimental air shower data. It can be described as a Poisson-like term with a normalization constant that depends on the zenith angle of the primary cosmic ray. This dependence reflects the increasing contribution to the signal of the muonic component of the shower, both due to the increasing muon/electromagnetic (e+- and gamma) ratio and muon track length with zenith angle.