Fluorescence photons produced in air by extensive air showers

The air fluorescence technique has long been used to detect extensive air showers and to reconstruct its geometry and energy. The fluorescence photon yield of an electron in air is of main importance in the reconstruction procedure. Historically, the fluorescence yield used in the reconstruction of the showers is approximated at all energies by that of an electron with kinetic energy of 80 MeV, because these are the most abundant in a shower. In this paper, we calculate the fluorescence yield taking into account the energy spectrum of electrons in showers initiated by proton and iron nuclei as a function of height. We compare our results with previous calculations based on mono energetic electrons (80 MeV) and a difference in excess of 8% is found. Finally, the influence of a more realistic fluorescence yield in the shower energy reconstruction is also discussed.