AIRFLY Collaboration, M. Ave, M. Bohacova, E. Curry, P. Di Carlo, C. Di Giulio, P. Facal San Luis, D. Gonzales, C. Hojvat, J. Hörandel, M. Hrabovsky, M. Iarlori, B. Keilhauer, H. Klages, M. Kleifges, F. Kuehn, S. Li, M. Monasor, L. Nozka, M. Palatka, S. Petrera, P. Privitera, J. Ridky, V. Rizi, B. Rouille D'Orfeuil, F. Salamida, P. Schovanek, R. Smida, H. Spinka, A. Ulrich, V. Verzi, C. Williams
A measurement of the absolute fluorescence yield of the 337 nm nitrogen band, relevant to ultra-high energy cosmic ray (UHECR) detectors, is reported. Two independent calibrations of the fluorescence emission induced by a 120 GeV proton beam were employed: Cherenkov light from the beam particle and calibrated light from a nitrogen laser. The fluorescence yield in air at a pressure of 1013 hPa and temperature of 293 K was found to be $Y_{337} = 5.61\pm 0.06_{stat} \pm 0.21_{syst}$ photons/MeV. When compared to the fluorescence yield currently used by UHECR experiments, this measurement improves the uncertainty by a factor of three, and has a significant impact on the determination of the energy scale of the cosmic ray spectrum.
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http://arxiv.org/abs/1210.6734
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