CMS Global Trigger Upgrade
Figure: CMS Global Trigger upgrade crate with prototype modules
When the LHC resumes its operation in 2015, the collision-energy will be increased from 8 TeV to 13 TeV, with a higher luminosity. These operating environments will provide new challenges for the CMS Trigger system. The CMS Level-1 trigger system will be upgraded to improve its performance for selecting interesting physics collisions and to operate within the predefined data-acquisition rate. To improve the performance of the Level-1 trigger system at high luminosity with large numbers of pile-up events, the electronics for the calorimeter, muon and global trigger systems will be replaced. The upgraded system will be flexible for implementing further rate reduction and efficiency improvements as algorithms improve. The flexibility will be accomplished by using high bandwidth optical links for most of the data communication between trigger cards, and by using modern, large FPGAs and large memory resources for the trigger logic.
The Global Trigger (GT) is the final step of the CMS Level-1 Trigger and implements a trigger menu, a set of selection requirements applied to the final list of objects from calorimeter and muon triggers to meet the physics objectives. The conditions for trigger object selection, with possible topological requirements on multi-object triggers, are combined by simple combinatorial logic (AND-OR-NOT-XOR) to form the algorithms. The most basic algorithms consist of applying ET or pT threshold to single objects. The present GT is comprised of several VME modules with FPGAs. The GT will be re-implemented on modern FPGA on an Advanced Mezzanice Card in a MicroTCA crate. The upgraded system will benefit from increased processing resources, enabling more algorithms at a time than previously possible, allowing CMS to be more flexible in how it handles the Trigger bandwidth. CMS also will be able to match different objects, e.g. muons with jets, with higher resolution and efficiency and be able to calculate more sophisticated quantities such as the mass of a pair of objects. In 2015, CMS plans to keep the present triggers running and commission the new ones simultaneously.