Infill Event Reconstruction

D. RAVIGNANI, D. MELO, E. COLOMBO, A. FERRERO, A. KRIEGER, I. SIDELNIK, B. WUNDHEILER, A. ETCHEGOYEN

Encuentro; Pierre Auger Internal GAP Note Nº 2009-116; 2009

This work looks at the reconstruction of events detected by the infill array. The existing main array reconstruction is not suitable for the infill because of 3 different issues. The first one is that it relies in the evaluation of the lateral distribution function (LDF) at 1000 m from the shower core (S (1000)). At the infill energy threshold of about 3 x 10 ^17 eV, one decade below the main array one, S (1000) can be as little 2 VEM. Given the large fluctuations and threshold effects for such vanishing signal, it is apparent that S (1000) cannot be a reliable energy estimator. The second issue is that the main array energy calibration is done for events above 3 x 10^18 eV, therefore there is no guarantee that it is still valid for infill energies. Finally, on a technical side, the main array LDF, optimised for a detector distance of 1500 m, has to be modified to work with the 750 m infill spacing. In this work we propose a new infill reconstruction using an infill optimized LDF with a shower ground parameter at 600 m from the shower axis. Next the infill is calibrated in energy using a novel method based on both hybrids and SD only events. The new infill reconstruction is then used to derive an energy histogram.