AIRFLY Collaboration , M. Ave , M. Boháčová , K. Daumiller , P. Di Carlo , C. Di Giulio , P. Facal San Luis , D. Gonzales , C. Hojvat , J. R. Hörandel , M. Hrabovský , M. Iarlori , B. Keilhauer , H. Klages , M. Kleifges , F. Kuehn , M. Monasor , L. Nožka , M. Palatka , S. Petrera , P. Privitera , J. Ridky , V. Rizi , B. Rouillé d'Orfeuil , F. Salamida , P. Schovánek , R. Šmida , H. Spinka , A. Ulrich , V. Verzi , C. Williams
19 January 2011
We have performed a measurement of the absolute yield of fluorescence photons at the Fermilab Test Beam. A systematic uncertainty at 5% level was achieved by the use of Cherenkov radiation as a reference calibration light source. A cross-check was performed by an independent calibration using a laser light source. A significant improvement on the energy scale uncertainty of Ultra-High Energy Cosmic Rays is expected.