A muon trigger upgrade with high transverse momentum resolution for the ATLAS detector at the High-Luminosity LHC

The Level-1 trigger for muons of the ATLAS experiment is based on trigger chambers with excellent time resolution which identifies muons coming from a particular beam crossing. To cope with a stringent constraint on the trigger rates expected at the phase II of the LHC, the socalled High-Luminosity LHC, it is proposed to include precision tracking chambers in the Level-1 muon trigger for improving the transverse momentum resolution. The rate of a single muon trigger with a transverse momentum threshold of 20 GeV is estimated to reduce to about half in an entire pseudorapidity region by introducing the proposed upgrade. An architecture of the electronics includes an additional priority readout chain, which is independent of the standard and asynchronous readout. A demonstrator of the frontend electronics has been developed and an initial test based on cosmic muons shows a resolution of position measurements consistent with a simulation.