This poster will present the design and the implementation of the firmware algorithms performing the electrons, photons, jets and tau leptons selection at the Level-1 CMS calorimeter trigger for the run II of the LHC. This new system is planned to be replacing the existing level-1 calorimeter trigger starting 2016. As the LHC restarts and delivers higher luminosity collisions, exceeding the design parameters, the current CMS trigger system will not be capable of maintaining the high efficiency required for the CMS physics program. The replacement of the trigger system is also a good opportunity to consider even more efficient ways of selecting electrons, photons, tau leptons, reconstructing jets and performing energy sums. In these intense conditions, the implementation of pile-up mitigation techniques is required to reach acceptable performance.
Modern technologies offer an effective solution to achieve these goals. The 2016 system being commissioned to run in parallel starting this fall will be based on the microTCA electronics standard. The innovative approach of the Time Multiplexed Trigger (TMT), which will be presented on the poster, allows to perform physics objects selections and pile-up mitigation in an optimized way.
The trigger primitives generated by the detector will be transmitted by newly installed optical link boards (4.5 to 6.4 Gb/s) replacing the existing copper cables (1.2 Gb/s), to the new microTCA crates. The system is based on custom designed AMC (Advanced Mezzanine Boards) with Xilinx Virtex 7 FPGAs. These boards provide up to 144 high-speed optical serial links, running at speeds up to 10 Gbps allowing to gather information from the entire calorimeter for each event in one FPGA, where sophisticated algorithms may be implemented. The complete view of the calorimeter will allow the trigger to compute global quantities such as the average energy density that can be used to estimate the pile-up level. The resulting increase in rejection power will permit the experiment keep low trigger thresholds on physics objects.
The firmware design benefits from an optimized approach to perform sums to build jet candidates and dynamic clustering to reconstruct the electron footprint. Tau leptons are built from basic clusters to improve the efficiency on all possible decay modes. Adapted calibration techniques are used to improve on the response and the enhanced granularity available allows to achieve excellent angular resolutions for these objects. The poster will present the details of the firmware algorithms and their performance that are beyond expectations for a Level-1 hardware based system. Particular emphasis is placed on the results from the undergoing final commissioning tests directly on the system.