Implementation in a sector of the CMS Drift Tube chambers of a muon tracking algorithm for Level 1 trigger during HL-LHC

To tolerate HL-LHC (High Luminosity Large Hadron Collider) data taking conditions the on detector electronics of the CMS (Compact Muon Solenoid) DT (Drift Tubes) chambers needs to be replaced during Long Shutdown 3 (LS3). A new system has been designed to comply with the increased occupancy in the chambers and acquisition rate in CMS, extracting maximal performance from the existing chambers, which will remain in place with similar performance. The new architecture ships all the time-digitized chamber hits to the backend where we expect to achieve resolutions comparable to the ones that the CPU-based High Level Trigger can obtain nowadays and allowing to combine information across chambers. In this way, the new system will provide improved performance with respect to present system, and in particular it will be more resilient to potential aging degradation. The first prototypes of the HL-LHC electronics for the CMS On detector Board for the Drift Tube chambers (OBDT) have been installed in one sector of DT chambers on the CMS detector and integrated in the central data acquisition and trigger system during LS2. An algorithm for the trigger primitive generation that runs on backend boards used for the DT Phase 1 upgrade (TM7, porting a Xilinx Virtex 7 FPGA) has been developed and implemented in firmware. They have operated together with the first backend prototypes for timing distribution and slow control. After a months-long data-taking campaign of cosmic rays in the underground cavern, the full chain has been commissioned, showing very good performance as expected from the Phase 2 design. We plan to run this Phase 2 parallel system in collisions during Run 3, which will allow to test final pre-production prototypes under realistic conditions (radiation, magnetic field) and further refine trigger algorithms.