New air fluorescence detectors employed in the Telescope Array experiment

TL;DR

This paper reports on the design, installation, and performance evaluation of new air fluorescence detectors used in the Telescope Array experiment to improve the measurement of ultra high energy cosmic rays.

Contribution

Introduction of newly designed fluorescence detectors and detailed analysis of their optical characteristics and performance in the TA experiment.

Findings

New FD detectors have high optical performance.

Monitored mirror reflectance remained stable during observations.

Detectors improved the accuracy of EAS measurements.

Abstract

Since 2007, the Telescope Array (TA) experiment, based in Utah, USA, has been observing ultra high energy cosmic rays to understand their origins. The experiment involves a surface detector (SD) array and three fluorescence detector (FD) stations. FD stations, installed surrounding the SD array, measure the air fluorescence light emitted from extensive air showers (EASs) for precise determination of their energies and species. The detectors employed at one of the three FD stations were relocated from the High Resolution Fly's Eye experiment. At the other two stations, newly designed detectors were constructed for the TA experiment. An FD consists of a primary mirror and a camera equipped with photomultiplier tubes. To obtain the EAS parameters with high accuracies, understanding the FD optical characteristics is important. In this paper, we report the characteristics and installation of new FDs and the performances of the FD components. The results of the monitored mirror reflectance during the observation time are also described in this report.