Upgrade of the CMS muon trigger system in the barrel region

Abstract

To maintain the excellent performance of the LHC during its Run-1 also in Run-2, the Level-1 Trigger of the Compact Muon Solenoid experiment underwent a significant upgrade. One part of this upgrade was the re-organisation of the muon trigger path from a subsystem-centric view in which hits in the drift tubes, the cathode strip chambers, and the resistive plate chambers were treated separately in dedicated track-finding systems, to one in which complementary detector systems for a given region (barrel, overlap, and endcap) are merged already at the track-finding level. This also required the development of a new system to sort as well as cancel-out the muon tracks found by each system. An overview will be given of the new track-finder system for the barrel region, the Barrel Muon Track Finder (BMTF) as well as the cancel-out and sorting layer, the upgraded Global Muon Trigger (\(\mu\)GMT). While the BMTF improves on the proven and well-tested algorithms used in the Drift Tube Track Finder during Run-1, the \(\mu\)GMT is an almost complete re-development due to the re-organisation of the underlying systems from complementary track finders to regional track finders. Additionally, the \(\mu\)GMT can calculate a muon isolation using energy information that will be received from the calorimeter trigger in the future. This information is added to the muon objects forwarded to the Global Trigger. Finally, first results of the muon trigger performance including the barrel region are shown. Both the trigger efficiency and the rate reduction show satisfactory performance, with improvements planned for the near future.