Measurement of the air fluorescence yield with the airlight experiment

The present uncertainties in the air fluorescence yield are the limiting factor for the energy reconstruction of ultra-high energy cosmic rays, measured by fluorescence telescopes. The AirLight experiment has measured the pressure and energy dependence of the air fluorescence yield for the eight strongest nitrogen transitions between 300 and 400 nm with an uncertainty of about 15%, for low energy electrons between 250 and 2000 keV. Furthermore the influence of water vapor has been studied. A new approach for the parametrization of the fluorescence yield has been used to analyze the data, resulting in a consistent description of the fluorescence yield with a minimal set of parameters. This paper explains the experimental method and summarizes the results.