After a two-year shutdown, the LHC restarted collisions in 2015, with higher proton–proton centre-of-mass energy (13 TeV) and increased instantaneous luminosity. The RAL CMS group participated in the upgrade of the so the Level-1 trigger system during 2015 and early 2016, in order to improve its efficiency for searches and precision measurements, compared with the previous run. The upgraded system is composed of a set of general-purpose boards, that follow the MicroTCA specification, connected by high-speed serial optical links, resulting in a more homogeneous system. This system contains the order of 100 boards connected by 3000 optical links, which must be controlled and monitored coherently. The experiment’s off-detector electronics transmit reduced-granularity data (trigger primitives) from the calorimeters and muon detectors to the trigger electronics over optical links. The trigger primitive data from different fiducial regions of the muon detectors — the barrel, end-cap, and overlap regions — are processed in three separate track finder subsystems; the resulting three sets of muon track candidates are combined in the micro-Global Muon Trigger. The calorimeter data is processed to reconstruct electrons, tau leptons and jets in a separate data path, consisting of two layers of electronics: a first layer that time multiplexes the data, and a second layer in which each electronic board processes the data from the entire calorimeter for every 9th event, in a round robin sequence. The particles reconstructed in the calorimeter and muon pathways are then combined in the micro-Global Trigger (μGT), which takes the decision of whether or not a proton–proton collision is a sufficiently interesting event, by applying kinematic and quality selection criteria on the received particle candidates.
Above is an image of MP7 (Master Processor, Virtex-7) processor card based on the Xilinx Virtex-7 FPGA used for the L1 Trigger upgrade