Performance Studies of Layered Water Cherenkov Detectors

TL;DR

This paper evaluates layered water Cherenkov detectors for ultra-high-energy cosmic ray observation, analyzing prototype performance, calibration, and design optimization for large-scale observatories like GCOS.

Contribution

It presents a decade of data from prototype tanks, compares performance with simulations, and explores design parameters for future large-area detectors.

Findings

Prototype tanks show consistent performance over 10 years.

Calibration methods align data with simulations.

Design recommendations for large-scale deployment are provided.

Abstract

Next-generation air-shower detectors, such as the Global Cosmic Ray Observatory (GCOS) and the Probing Extreme PeVatron Sources (PEPS) experiment, are considering water-Cherenkov detectors as a base design. A key factor in improving the sensitivity to ultra-high-energy gamma rays and to the mass composition of ultra-high-energy cosmic rays is the ability to measure the muonic content of air showers. To address this, a layered water Cherenkov tank design has been previously proposed. The water volume of the tank is divided into two optically separated layers. The electromagnetic component of the shower is mostly absorbed in the top layer, while the bottom layer records the light produced by through-going muons. Two prototype tanks were deployed at the Pierre Auger Observatory site in 2014 and have been recording data for more than 10 years. We present the performance of the prototype tanks and compare it with simulations, focusing mostly on the calibration. We investigate different dimensions for the water volumes. For the GCOS Observatory, one important challenge is to cover extremely large surfaces of 40000 km$^2$ to 60000 km$^2$ and achieve 100% efficiency at 10 EeV. Based on the size of the footprint of air-showers, we compute the number and spacing of detectors needed to fulfill the GCOS requirements.