The new APD-Based Readout of the Crystal Barrel Calorimeter -- An Overview

TL;DR

This paper presents an upgraded APD-based readout system for the Crystal Barrel calorimeter, enhancing trigger integration and neutral state sensitivity through FPGA processing and temperature stabilization.

Contribution

It introduces a novel APD-based readout with FPGA cluster finder and temperature compensation, improving detector performance and trigger capabilities.

Findings

Enhanced trigger integration with FPGA processing

Improved sensitivity for neutral final states

Effective temperature stabilization for APDs

Abstract

The Crystal Barrel is an electromagnetic calorimeter consisting of 1380 CsI(Tl) scintillators, and is currently installed at the CBELSA/TAPS experiment where it is used to detect decay products from photoproduction of mesons. The readout of the Crystal Barrel has been upgraded in order to integrate the detector into the first level of the trigger and to increase its sensitivity for neutral final states. The new readout uses avalanche photodiodes in the front-end and a dual back-end with branches optimized for energy and time measurement, respectively. An FPGA-based cluster finder processes the whole hit pattern within less than 100 ns. The important downside of APDs -- the temperature dependence of their gain -- is handled with a temperature stabilization and a compensating bias voltage supply. Additionally, a light pulser system allows the APDs' gains to be measured during beamtimes.