A novel design for 100 meter-scale water attenuation length measurement and monitoring

Abstract

Water Cherenov detector is a vital part in most of neutrino or cosmic ray research. As detectors grow in size, the water attenuation length (WAL) becomes increasingly essential for detector performance. It is essential to measure or monitor the WAL. There are two ways to measure WAL, one is to take a water sample from the detector and measure it in the WAL measurement device, and the other is to put the device directly into the water Cherenkov detector. For the device in the water, the Super-Kamiokande experiment achieved WAL measurement capability near 100 meters with a moving light source up and down. A novel system has been proposed to address the challenge of investigating long WAL. This system focuses on ample water Cherenkov detectors and features a fixed light source and photomultiplier tubes (PMTs) at varying distances, eliminating the need for moving parts. Each component, including LED, diffuse ball, PMTs, and fibers, is introduced to explain uncertainty control. Based on lab tests, the measurement uncertainty of each PMT channel has been controlled within 5%. Additionally, camera technology is also used during the evaluation of the system uncertainty, which has the potential to replace PMTs in the future for this measurement. Monte Carlo simulations have shown that the system can achieve a 5% uncertainty at WAL of 80 meters and 8% at WAL of 100 meters. This system can be used in experiments with large Cherenkov detectors such as JUNO-water veto and Hyper-K.