Abstract
Extensive air showers initiate the fluorescence emissions from nitrogen molecules in air. The UV-light is emitted isotropically and can be used for observing the longitudinal development of extensive air showers in the atmosphere over tenth of kilometers. This measurement technique is well-established since it is exploited for many decades by several cosmic ray experiments. However, a fundamental aspect of the air shower analyses is the description of the fluorescence emission in dependence on varying atmospheric conditions. Different fluorescence yields affect directly the energy scaling of air shower reconstruction. In order to explore the various details of the nitrogen fluorescence emission in air, a few experimental groups have been performing dedicated measurements over the last decade. Most of the measurements are now finished. These experimental groups have been discussing their techniques and results in a series of Air Fluorescence Workshops commenced in 2002. At the 8$^{\rm{th}}$ Air Fluorescence Workshop 2011, it was suggested to develop a common way of describing the nitrogen fluorescence for application to air shower observations. Here, first analyses for a common treatment of the major dependences of the emission procedure are presented. Aspects like the contributions at different wavelengths, the dependence on pressure as it is decreasing with increasing altitude in the atmosphere, the temperature dependence, in particular that of the collisional cross sections between molecules involved, and the collisional de-excitation by water vapor are discussed.
Highlights
The detection of ultra-high energy cosmic rays is very challenging and it is a major key to answer open questions in astroparticle physics
The AIRFLY Collaboration has presented an own absolute yield for the 337.1 nm line, which is 7.07 337/MeV at 800 hPa and 293 K, corresponding to 5.60(1) 337/MeV at 1013 hPa and 293 K [15, 54]. Reconstructions using this absolute yield together with the reference description are labeled with SFYRef−AIRFLYScale
We presented a first suggestion of a common reference description of the fluorescence emission in air which is widely used for high-energy cosmic ray observations
Summary
The detection of ultra-high energy cosmic rays is very challenging and it is a major key to answer open questions in astroparticle physics. For detecting ultra-high energy cosmic rays, extensive air showers initiated in the Earth’s atmosphere are observed. For determining the absolute fluorescence yield, its emission spectrum, as well as its dependence on varying atmospheric conditions to an appropriate level of precision, several experimental groups have been performing dedicated laboratory measurements over the last decade. The experimental efforts have been supplemented by several simulations and air shower reconstruction studies These groups have been discussing their techniques and data in a series of Air Fluorescence Workshops (AFW) commenced in Utah, 2002 [9]. The two dependences are being discussed to be able to compare reconstructions of extensive air showers based on a common altitude-dependent shape of the fluorescence emission. The challenge of determining the absolute fluorescence yield is being addressed which directly introduces the scaling of the reconstructed primary energy of air showers
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