The Large Hadron Collider is a large particle accelerator at the CERN research laboratory, designed to provide particle physics experiments with collisions at unprecedented centre-of-mass energies. For its second running period both the number of colliding particles and their collision energy were increased. To cope with these more challenging conditions and maintain the excellent performance seen during the first running period, the Level-1 trigger of the Compact Muon Solenoid experiment — a sophisticated electronics system designed to filter events in real-time — was upgraded. This upgrade consisted of the complete replacement of the trigger electronics and a full redesign of the system’s architecture. While the calorimeter trigger path now follows a time-multiplexed processing model where the entire trigger data for a collision are received by a single processing board, the muon trigger path was split into regional track finding systems where each newly introduced track finder receives data from all three muon subdetectors for a certain geometric detector slice and reconstructs fully formed muon tracks from this. In contrast, the system in operation during the first data taking period was built around subdetector-specific track finders whose output tracks were merged in the Global Muon Trigger. This restructuring of the muon trigger required a novel system to receive muon objects from the track finding layer, remove any duplicate tracks, and forward the best-reconstructed objects to the global decision layer. The upgraded Global Muon Trigger (μGMT) was designed to satisfy the requirements for such a system. It receives muon track data from all regional track finder processors as well as energy information from the final stage of the calorimeter trigger. These muon tracks are ranked and sorted, while in parallel their azimuthal coordinate is corrected and duplicate muon tracks are removed. An isolation variable using the calorimetric information is computed before the eight highest-rankedmuon tracks are sent to the upgraded Global Trigger (μGT). The μGT then determines whether a readout process shall be initiated by applying complex algorithms on the muon tracks as well as on data received from the calorimeter trigger chain. This thesis presents the design and development of the μGMT, outlining the requirements as well as challenges encountered during development of the upgraded trigger. Furthermore, the excellent performance of the new system is demonstrated in the context of studies on quarkonia: Both the impact of the improved duplicate removal system as well as of the correction of the azimuthal coordinate are evaluated and shown to improve upon the performance demonstrated by the original Level-1 trigger. Additionally, a simple scheme that increases the purity of dedicated trigger algorithms to select J/ψ mesons by requiring the presence of two oppositely charged muons is presented and assessed.

Upgrade of the Global Muon Trigger for the Compact Muon Solenoid experiment at CERN

The present RPC Link System has been servicing as one of the CMS subsystems since installation in 2008. Although the current Link System has been functioning well for the past 13 years, the aging of its electronic components and lack of radiation hard ASICs could present problems for future operations. Additionally, the needs to have a more robust control interface against electromagnetic interference, to improve the trigger performance with finer time granularity and to incorporate a higher bandwidth transmission lines led the idea of upgrading the Link System for the HL-LHC. This paper reviews the features of the recently developed prototype of the new Link System.

CMS phase-II upgrade of the RPC Link System

The CMS experiment implements a two-level triggering system composed of Level-1, instrumented by custom-design hardware boards, and a software High Level Trigger. To cope with the more challenging luminosity conditions, a new Level-1 architecture has been deployed during run II. This new architecture exploits in a better way the redundancy and complementarity of the three muon subsystems: Cathode Strip Chambers (CSC), Drift Tubes (DT) and Resistive Plate Chambers (RPC). The role of each subsystem in the Level-1 Muon Trigger is described here, highlighting the contribution from the RPC system. Challenges brought by the HL-LHC environment and new possibilities coming from detector and trigger upgrades are also discussed.

https://biblio.ugent.be/publication/8702609/file/8703232.pdf

RPC system in the CMS Level-1 Muon Trigger

During LHC Run II the centre-of-mass energy of pp collisions has increased up to 13 TeV and the instantaneous luminosity has progressed towards 2×10^34 cm^−2 s^−1. In order to guarantee a successful and ambitious physics programme under these conditions, the CMS trigger system system has been upgraded. The upgraded CMS Level-1 trigger is designed to improve performance at high luminosity and large number of simultaneous inelastic collisions per crossing. The trigger design, implementation and commissioning are summarised and early performance results are described.

/pdf/the-cms-level-1-trigger-for-lhc-run-ii-4nkuokbk8x.pdf

The CMS Level-1 Trigger for LHC Run II

https://digitalcommons.fiu.edu/cgi/viewcontent.cgi?article=1035&context=physics_fac

Search for lepton-flavour-violating decays of the Higgs boson

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.

/pdf/upgrade-of-the-cms-muon-trigger-system-in-the-barrel-region-2wpghkjvue.pdf

Upgrade of the CMS muon trigger system in the barrel region

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Upgrade of the CMS muon trigger system in the barrel region