R&D of the cluster finding algorithm for CMS iRPC detector

Abstract

The Compact Muon Solenoid (CMS) experiment will undergo phase-II upgrade to enhance the capacity of detectors in the High-Luminosity Large Hadron Collider era. An important extension involves the installation of the Improved Resistive Plate Chambers (iRPC) in the most forward part of the endcap muon system. The iRPC detector addresses the efficiency drop experienced by the current CMS trigger system for single muon triggers in the high pseudorapidity region. It features a double-ended read-out method, allowing the determination of the hit position along the strip using the time difference between signals from both ends. This feature provides precise spatial information for clustering. To utilize this feature and integrate iRPC cluster information into the CMS trigger system, this paper proposes a 2-Dimensional (2D) cluster-finding algorithm. This algorithm provides the 2D coordinates to CMS trigger system, with each cluster being timestamped to reduce time ambiguity in endcap trajectory reconstruction. The proposed algorithm was implemented in the firmware of the iRPC Back-End Electronics and evaluated using a dedicated cosmic muon setup. The results show a position precision of 2.55 cm and an algorithm efficiency better than 99%, demonstrating the algorithm's potential to improve muon detection and trigger efficiency in the CMS endcap region.