The CMS Level-1 trigger system for LHC Run II

The Compact Muon Solenoid (CMS) experiment implements a sophisticated two-level online selection system that achieves a rejection factor of nearly 10(5). During Run II, the LHC has increased the centre-of-mass energy of proton-proton collisions up to 13 TeV and may progressively reach an instantaneous luminosity of 2 x 10(34) cm(-2) s(-1) or higher. In order to guarantee a successful and ambitious physics programme under this intense environment, the CMS Trigger and Data acquisition system has been upgraded. The upgraded CMS Level-1 (L1) trigger benefits from the recent mu TCA technology and is designed to maintain the performance under high instantaneous luminosity conditions. More sophisticated, innovative algorithms are now the core of the first decision layer of CMS: this drastically reduces the trigger rate and improves the trigger efficiency for a wide variety of physics processes. In this document, we present the overall architecture of the upgraded Level-1 trigger system. The performance of single object triggers, measured on collision data recorded during the 2016 running period, are also summarised.