Analysis of shower size as estimator of extensive air shower energy
  The fluorescence technique has been successfully used to detect ultrahigh energy cosmic rays by indirect measurements. 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. However the influence of shower fluctuations and the very possible presence of different nuclear species in the primary cosmic ray spectrum make the estimate of the shower energy from the fluorescence data analysis a difficult task. We investigate the potential of shower size at maximum depth as estimator of shower energy. The detection of the fluorescence light is simulated in detail and the reconstruction biases are carefully analyzed. We extend our calculations to both Auger and EUSO experiments. This kind of approach is of particular interest for showers that are not fully contained inside the field of view of the detector. 
Vitor de Souza, Jeferson A. Ortiz, Gustavo Medina-Tanco, Federico   Sanchez