# Air Shower Observation by a Simple Structured Fresnel lens Telescope with Single Pixel for the Next Generation of Ultra-High Energy Cosmic Ray Observatory

## TL;DR

This paper introduces CRAFFT, a simple, cost-effective fluorescence detector with a Fresnel lens and single pixel, capable of observing air showers from ultra-high energy cosmic rays, promising to advance future UHECR observatories.

## Contribution

The paper presents CRAFFT, a novel, low-cost fluorescence detector with a simple structure and single pixel, suitable for large-scale UHECR observatories, demonstrated through successful field tests.

## Key findings

- Successfully observed ten air-shower events with CRAFFT.
- Demonstrated CRAFFT's potential for cost-effective, large-scale UHECR detection.
- Proved CRAFFT's capability to observe air shower longitudinal development.

## Abstract

Improved statistics and mass-composition-sensitive observation are required to clarify the origin of ultra-high energy cosmic rays (UHECRs). Inevitably in the future, the UHECR observatories will have to be expanded due to the small flux; however, the upgrade will be expensive with the detectors currently in use. Hence, we are developing a new fluorescence detector for UHECR observation. The proposed fluorescence detector, called cosmic ray air fluorescence Fresnel-lens telescope (CRAFFT), has an extremely simple structure and can observe the longitudinal development of an air shower. Furthermore, CRAFFT has the potential to significantly reduce costs for the realization of a huge observatory for UHECR research. We deployed four CRAFFT detectors at the Telescope Array site and conducted the test observation. We have successfully observed ten air-shower events using CRAFFT. Thus, CRAFFT can be a solution to realize the next generation of UHECR observatories.