The Monitoring System of the End-Cap Calorimeter in the Belle II experiment

TL;DR

This paper describes the redesign and implementation of a monitoring system for the End-Cap Calorimeter in the Belle II experiment, focusing on environmental sensors for CsI(Tl) crystals to ensure optimal detector performance.

Contribution

It introduces a new hardware and software architecture for environmental monitoring of the calorimeter, utilizing embedded systems and EPICS for remote control.

Findings

Successful deployment of the monitoring system for 2112 crystals

Enhanced environmental data acquisition and control capabilities

Improved detector safety and performance monitoring

Abstract

The Belle II experiment is presently in phase-2 operation at the SuperKEKB electron-positron collider in KEK (Tsukuba, Japan). The detector is an upgrade of the Belle experiment at the KEKB collider and it is optimized for the study of rare B decays, being also sensitive to signals of New Physics beyond the Standard Model. The Electromagnetic Calorimeter (ECL) is based on CsI(Tl) scintillation crystals. It splits in a barrel and two annular end-cap regions, these latter named Forward and Backward, according to the asymmetric design of the collider. CsI(Tl) crystals deliver a high light output at an affordable cost, however their yield changes with temperature and can be permanently damaged by humidity, due to the strong chemical affinity for moisture. Each ECL region is then equipped with thermistors and humidity probes to monitor environmental data. While sensors and cabling have been inherited from the original Belle design, the ECL monitoring system has been fully redesigned. In this paper, we present hardware and software architecture deployed for the 2112 CsI(Tl) crystals arranged in the Forward and Backward end-caps. Single-Board Computers (SBCs) have been designed ad-hoc for embedded applications. For sensor read-out, a data-acquisition system based on 24-bit ADCs with local processing capability has been realized and interfaced with the SBCs. EPICS applications send data across the Local Area Network for remote control and display.