A novel FPGA-based track reconstruction approach for the level-1 trigger of the CMS experiment at CERN

The Compact Muon Solenoid (CMS) experiment at CERN is scheduled for a major upgrade in the next decade in order to meet the demands of the new High Luminosity Large Hadron Collider. Amongst others, a new tracking system is under development including an outer tracker capable of rejecting low transverse momentum particles by looking at the coincidences of hits (stubs) in two closely spaced sensor layers in the same tracker module. Accepted stubs are transmitted off-detector for further processing at 40 MHz. In order to maintain under the increased luminosity the Level-1 trigger rate at 750 kHz, tracker data need to be included in the decision making process. For this purpose, a system architecture has to be developed that will be able to identify particles with transverse momentum above 3 GeV/c by building tracks out of stubs, while achieving an overall processing latency of maximum 4us. Targeting these requirements the current paper presents an FPGA-based track finding architecture that identifies track candidates in real-time and bases its functionality on a fully time-multiplexed approach. As a proof of concept, a hardware system has been assembled targeting the MP7 MicroTCA processing card that features a Xilinx Virtex-7 FPGA, demonstrating a realistic slice of the track finder. The paper discusses the algorithms' implementation and the efficient utilisation of the available FPGA resources, it outlines the system architecture, and presents some of the hardware demonstrator results.