Precise measurement of the absolute fluorescence yield of the 337 nm band in atmospheric gases

TL;DR

This paper precisely measures the absolute fluorescence yield of the 337 nm nitrogen band in atmospheric gases, reducing uncertainty and improving cosmic ray energy scale calibration.

Contribution

It provides a new, highly accurate measurement of the fluorescence yield using two independent calibration methods, enhancing the precision for cosmic ray detection.

Findings

Fluorescence yield in air at 1013 hPa and 293 K is 5.61 photons/MeV.

Uncertainty is reduced by a factor of three compared to previous values.

Improves the accuracy of cosmic ray energy measurements.

Abstract

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.