Light Monitoring System for the Lead Tungstate Calorimeter in Hall D at Jefferson Lab

TL;DR

This work presents a light monitoring system (LMS) for the GlueX Hall D PbWO4-based electromagnetic calorimeter, enabling real-time performance tracking and PMT gain calibration. The LMS uses 25 blue LEDs, an integrating sphere, and 1650 acrylic fibers to deliver controlled light to 1596 calorimeter modules, with reference PMTs and an alpha-source unit to monitor stability. Integrated into the GlueX trigger, the LMS operated continuously during detector commissioning and the first physics run, delivering stable, sub-percent fluctuations and enabling gain corrections via pi0 calibration. The system enhances calorimeter reliability and enables real-time calibration for accurate energy reconstruction in high-rate environments.

Abstract

A new electromagnetic calorimeter composed of 1596 lead tungstate (PbWO$_4$) scintillating crystals has been constructed for the GlueX detector in Hall D at Jefferson Lab. The calorimeter is equipped with a light monitoring system that uses light-emitting diodes. The light monitoring system was fabricated, installed, and integrated into the GlueX trigger system. It was successfully operated during detector commissioning and data collection. The paper describes the design, installation, and performance of the light monitoring system.

Figures (13)

• Figure 1: Schematic view of the ECAL light monitoring system.
• Figure 2: The printed circuit board with the light monitoring system driver components and footprints for 25 LEDs in the middle.
• Figure 3: Schematic view of the LED driver designed at Jefferson Lab. The main components are the trigger pulse shaper, power buffers for 25 LEDs, and individual LED drivers.
• Figure 4: Signal waveform digitized by a flash ADC, induced by the LMS (left) and by scintillation light in the PbWO$_4$ crystal (right).
• Figure 5: The plastic cap with the inserted optical fiber glued to the face of the PbWO$_4$ crystal.