Speaker
Description
The CMS endcap calorimeter upgrade for the high-luminosity LHC, the High Granularity Calorimeter (HGCAL), is starting a major test programme for large pieces of the detector, which includes beam and cosmic testing. The asynchronous nature of cosmic and beam triggers relative to the detector’s reference clock poses challenges in capturing signal peaks accurately with consequences for system validation and characterization. This work presents the development, testing and proposed updates of a system that has been designed for these HGCAL large-scale tests, allowing both external and self-triggering. The external trigger system aims to accurately measure trigger particle arrival times with respect to the detector reference clock. The trigger originates from PMT-coupled plastic scintillators placed in the beamline upstream of the detector or above the stack of production units. An innovative external trigger capture and time-of-arrival recording system was developed using CERN’s Low-Power GBT (LpGBT) ASIC, avoiding the need for dedicated TDC hardware or FPGA-based processors. The LpGBT is widely used across LHC experiments and typically records digitized data from front-end ASICs at up to 1.28 Gbps, transmitting it over high-speed electrical links to the back-end electronics with a jitter-optimized, fixed-phase recovered clock. In the test system, the external trigger capture uses a discriminated scintillator signal in place of the ASIC data, resulting in the signal being sampled with ~800 ps resolution. It uses a custom setup including an lpGBT development board and a level translator circuit. In the back-end, firmware implements windowed rising-edge detection, programmable delay chains, timestamp extraction, and re-trigger suppression via veto logic. The external trigger system has been successfully deployed in recent HGCAL beam test campaigns, demonstrating precise timing and reliable operation. It offers a versatile, low-latency solution for precise external timing and triggering in HGCAL operations and its integration with existing lpGBT infrastructure simplifies deployment and scalability. Complementing this, a self-trigger firmware module generates triggers based on applying thresholds to local sums of the HGCAL recorded energy, with capabilities for channel masking and latency matching across the detector. The self-trigger functionality enables the study of spurious events and system performance, such as non-Gaussian noise tails, independent of the external trigger.
Future developments will enhance capabilities for complex multi-unit systems and include next-generation DAQ hardware common across CMS, contributing to optimizing the eventual full-size HGCAL performance in CMS.
| Position | Electronics Engineer |
|---|---|
| Affiliation | Imperial College London |
| Country | United Kingdom |