Response curves of the surface modules of the Pierre Auger Observatory and the contribution of the hadronic component to the total signal of extensive showers

Full text: At large distances from the shower's core, is generally said that the electromagnetic and muonic components are responsible for most of the signal detected and the contribution of hadrons is irrelevant. In fact, looking at the events generated by the simulations of showers, we see an average number of hadrons which is small compared to other components. On the other hand, the important factor to be considered is the fraction of energy they carry. Geant4 full simulations of shower particles interacting in the surface module are very time consuming. To overcome this difficulty, we produced a set of response curves that can replace the corresponding full simulations. To include albedo phenomena, we include a soil layer as a new target for hadronic interactions, with the detailed treatment of hadron interactions available in Geant4 tool kit. The response curves for each particle type were obtained with full runs of Geant4 in the new setup. We will present this parametrization, which reduce the processing time by factors larger than 1000 times. These response curves were implemented in the tool kit Offline, developed by the collaboration to simulate/reconstruct the development of air showers. The Geant4 class corresponding to the surface module was replaced by our parametrization, while the rest of the simulation chain remained unchanged. The main focus of this work are the interactions of the hadronic component, in the tank and in the soil target below the tank. Those were obtained with the new setup and compared to the results from the original version of Offline. To assess the contribution of hadrons, we also studied the contribution of other components under the same conditions, so we can to obtain always the effect of hadronic interactions compared with the other components. We make a comparison between the energy reconstructed by the original Offline (with no changes) and the Offline with the implementation of our parameterization. We can infer the effect of hadronic interactions on the reconstruction of the primary particle energy, not only on its average value, but also in the corresponding fluctuation. This effect can demand a correction in the primary energy. (author)