The fluorescence yield of air excited by electrons measured with the AIRFLY experiment

A very direct way to observe ultra high energy cosmic rays is the fluorescence technique. Fluorescence detectors are already used in various experiments since the early eighties, the latest being the Pierre Auger Observatory. The most important parameter for the description of the fluorescence light detected is the fluorescence yield that defines how much light a particle causes on its way through gas. The fluorescence yield depends on temperature, pressure, gas composition and energy of the exciting particle. Also, the fluorescence yield is a major source of uncertainty in the reconstruction of the primary energy, because up to now its value is only determined within around 15%. This thesis describes the AIRFLY experiment that was set up to determine the fluorescence yield precisely. The pressure dependence of 18 spectral lines in the range of 280 nm to 430 nm has been determined using high resolution spectra. The spectral distribution of the fluorescence light in air has been measured and the effect of argon has been found to be negligible. The proportionality of the fluorescence yield to the energy deposit of the electrons has been confirmed between 1 MeV and 3 MeV. Adopting an absolute scale for the fluorescence yield at 337 nm as given by Nagano et al., the consequences of this works results for cosmic-ray measurements has been investigated. (orig.)