Average value of available measurements of the absolute air-fluorescence yield

TL;DR

This paper updates and analyzes measurements of the air-fluorescence yield, providing a refined average value with a 5% uncertainty, crucial for cosmic ray energy calibration.

Contribution

It offers a revised average fluorescence yield value by applying corrections and statistical analysis to previous measurements, improving consistency among experiments.

Findings

Average fluorescence yield: 5.45 ph/MeV at 1013 hPa and 293 K.

Spectral interval 300-420 nm: 20.1 ph/MeV.

Uncertainty reduced to 5%, compatible with AIRFLY results.

Abstract

The air-fluorescence yield is a key parameter for determining the energy scale of ultra-high-energy cosmic rays detected by fluorescence telescopes. A compilation of the available measurements of the absolute air-fluorescence yield normalized to its value in photons per MeV for the 337 nm band at given pressure and temperature has been recently presented in Ref. [1]. Also, in that paper, some corrections in the evaluation of the energy deposited in the corresponding experimental collision chambers have been proposed. In this note this comparison is updated. In addition, a simple statistical analysis is carried out showing that our corrections favor the compatibility among the various experiments. As a result, an average value of 5.45 ph/MeV for the fluorescence yield of the 337 nm band (20.1 ph/MeV for the spectral interval 300-420 nm) at 1013 hPa and 293 K with an uncertainty of 5% is found. This result is fully compatible with that recently presented by the AIRFLY collaboration (still preliminary) in such a way that including this latest result could even lowered the final uncertainty below the 5% level with high reliability.