The CMS level-1 calorimeter trigger upgrade for the run II of the LHC

The CMS experiment has implemented a sophisticated two-level online selection system that achieves a rejection factor of nearly 10⁵. The first level (L1) is based on coarse information coming from the calorimeters and the muon detectors while the High-Level Trigger combines fine-grain information from all sub-detectors. During Run II, the LHC will increase its centre-of-mass energy up to 13 TeV and progressively reach an instantaneous luminosity of 2×34 cm^-2s^-1. In order to guarantee a successful and ambitious physics programme under this intense environment, the CMS Trigger and Data acquisition system must be consolidated. In particular the L1 calorimeter trigger hardware and architecture will be modified. The goal is to maintain the current thresholds (e.g., for electrons and photons) and improve the performance for the selection of tau leptons. This can only be achieved by designing an updated trigger architecture based on the recent microTCA technology. Racks can be equipped with fast optical links and latest generation FPGAs can be used. Sophisticated object reconstruction algorithms as well as online pile-up corrections can thus be envisaged. The plan to consolidate the CMS trigger system will be presented as well as the recent hardware and firmware developments. Algorithms to select efficiently electrons and photons, will also be presented along with the expected performance.