Abstract
Results from the completed Phase 1 Upgrade of the Compact Muon Solenoid (CMS) Level-1 Calorimeter Trigger are presented. The upgrade was performed in two stages, with the first running in 2015 for proton and heavy ion collisions and the final stage for 2016 data taking. The Level-1 trigger has been fully commissioned and has been used by CMS to collect over 43 fb−1 of data since the start of the Run II of the Large Hadron Collider (LHC). The new trigger has been designed to improve the performance at high luminosity and large number of simultaneous inelastic collisions per crossing (pile-up). For this purpose it uses a novel design, the Time Multiplexed Trigger (TMT), which enables the data from an event to be processed by a single trigger processor at full granularity over several bunch crossings. The TMT design is a modular design based on the μTCA standard. The trigger processors are instrumented with Xilinx Virtex-7 690 FPGAs and 10 Gbps optical links. The TMT architecture is flexible and the number of trigger processors can be expanded according to the physics needs of CMS. Sophisticated and innovative algorithms are now the core of the first decision layer of the experiment. The system has been able to adapt to the outstanding performance of the LHC, which ran with an instantaneous luminosity well above design. The performance of the system for single physics objects are presented along with the optimizations foreseen to maintain the thresholds for the harsher conditions expected during the LHC Run II and Run III periods.
Highlights
The Level-1 trigger has been fully commissioned and has been used by Compact Muon Solenoid (CMS) to collect over 43 fb−1 of data since the start of the Run II of the Large Hadron Collider (LHC)
For this purpose it uses a novel design, the Time Multiplexed Trigger (TMT), which enables the data from an event to be processed by a single trigger processor at full granularity over several bunch crossings
The TMT architecture is exible and the number of trigger processors can be expanded according to the physics needs of CMS
Summary
The upgrade to the Level-1 calorimeter trigger system is certainly motivated by the need to preserve the trigger acceptance for physics. A single electron trigger of 20 GeV threshold would give a rate equivalent to almost half the total Level-1 bandwidth while jets and energy sums trigger rate would scale rapidly with pile-up and could not be sustained at all. In these intense conditions, the implementation of pile-up mitigation techniques was required already at Level-1 to reach acceptable performance. The rst stage was a partial upgrade that went online during the spring of 2015 [3]. The second stage was a full upgrade of the trigger system that started operations in March 2016. It is referred as the upgraded system in the rest of this document
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