CMS ECAL: Meeting the trigger performance challenges of Run 3

Northeastern University

^* e-mail: john.dervan@cern.ch

Published online: 7 March 2025

Abstract

The CMS electromagnetic calorimeter (ECAL) at the CERN LHC is a high-resolution crystal calorimeter equipped with fast digital signal processing algorithms for measuring the energy and timing of calorimeter deposits. These trigger primitives are sent to the Level-1 trigger system at a rate of 40 MHz to help decide whether to store the event data offline. This paper summarizes the ECAL trigger performance during LHC Run 3 (2022+), highlighting enhanced calibration methods for trigger primitives. A key focus is the commissioning of a new automated procedure for deriving, validating, and deploying time-dependent response corrections using in-situ measurements from a dedicated laser monitoring system. Additionally, the rejection of unwanted large signals (“spikes”) caused by hadronic deposits on the APD photodetectors in the ECAL barrel region (<η< 1.48) has been a persistent issue since 2009. The evolution of spike rejection techniques in ECAL’s on-detector and o↵-detector electronics, along with the potential of currently unused features of the ECAL electronics to further enhance spike rejection, will be discussed.