AIRFLY: Measurement of the uorescence yield in atmospheric gases

The goal of the AIRFLY (AIR FLuorescence Yield) experiment is to measure the fluorescence yield (FLY) induced by electrons in air to better than 10% precision. A detailed knowledge of the fluorescence emission characteristics is crucial for UHECR (Ultra High Energy Cosmic Ray) air shower energy reconstruction using the fluorescence technique. AIRFLY has been taking data at the Beam Test Facility (BTF) of the INFN Laboratori Nazionali di Frascati, Italy. The dependence of FLY on the atmospheric gas pressure and temperature has been studied. The dependence on electron energy has been measured in the range 50-420 MeV. A new method of absolute calibration by comparison with Cerenkov emission has been investigated. The status of the experiment and the results achieved so far are presented.