Analysis of shower size as estimator of extensive air shower energy

Presenter: V. de Souza (vitor@astro.iag.usp.br)The fluorescence technique has been successfully used to det ect ultrahigh energy cosmic rays by indirectmeasurements. The underlying idea is that the number of charged particles in the atmospheric shower, i.e,its longitudinal profile, can be extracted from the amount of emitted nitrogen fluorescence light. Howeverthe influence of shower fluctuations and the very possible pre sence of different nuclear species in the primarycosmic ray spectrummakethe estimate of the showerenergyfromthe fluorescencedata analysis a difficult task.We investigate the potential of shower size at maximum depth as estimator of shower energy. The detection ofthe fluorescence light is simulated in detail and the reconst ruction biases are carefully analyzed. We extend ourcalculations to both HiRes and EUSO experiments. This kind of approach is of particular interest for showersthat are not fully contained inside the field of view of the det ector.