Hardware Demonstrator Of The Phase-II ATLAS MDT Trigger Processor

The first level (L0) muon trigger of the ATLAS experiment will be upgraded to operate at the High Luminosity LHC. The selectivity of the current L0 muon trigger is limited by the moderate spatial resolution of RPC and TGC. The MDT chambers currently used for precision tracking will be therefore included to improve the momentum resolution and the redundancy. In the Phase-II scheme, the MDT trigger processors will receive MDT hits from the detectors and match them to the trigger candidates (seeds) from the RPC and TGC+NSW trigger chambers. These seeds provide a region of interest (RoI) and the identification of the bunch crossing from which the muon originated. This is the t0 for computing the MDT drift time from the arrival time of the hit. MDT hits matched to the RoI are then used by the MDT trigger algorithm to improve the momentum resolution, by forming track segments and joining them together for momentum determination. A hardware demonstrator of the MDT trigger processor, based on a common ATCA platform known as "APOLLO", is currently under production. It consists of two separate modules called the "Command Module" and "Service Module", and it is based on FPGA technology. A description of the explored algorithms for the MDT track reconstruction is presented. The achieved trigger performance allow to reconstruct muon tracks at the first-level with an average momentum resolution of about 6% and a trigger efficiency above 95% for muons with a transverse momentum of 20 GeV.