A Muon Trigger with high pT-resolution for Phase-II of the LHC Upgrade, based on the ATLAS Muon Drift Tube Chambers

The ATLAS Muon Trigger in the ATLAS end-cap region is based on Thin Gap Chambers (TGC) which have an excellent time resolution but a moderate spatial resolution. The Muon Trigger efficiency curves show that for a transverse momentum ($p_{t}$) threshold of 20 GeVc$^{-1}$ the trigger rate is mainly dominated by muons with a $p_{t}$ between 10 GeVc$^{-1}$ and 20 GeVc$^{-1}$. To cope with the expected Muon Trigger rate at HL-LHC luminosities, we propose to include the precision tracking chambers (MDT) in the Muon Trigger. According to a potential study based on ATLAS data and assuming the HL-LHC scenario, this leads to a dramatical reduction of the Muon Trigger rate below the nominal threshold. As the already existing MDT chamber read-out chain is not capable of reading out the MDT fast enough to be used for the Muon Trigger, an additional fast read-out (FRO) chain with moderate spatial resolution but low latency is necessary. To conduct fast track reconstruction and muon $p_{t}$ determination with the data acquired by the FRO, we propose to use histogram based pattern recognition. Simulation studies with single muon tracks show that this algorithm is capable of providing the necessary rate reduction below the nominal Muon Trigger threshold. We designed and tested an MDT read-out demonstrator setup which includes the additional FRO. This setup has been tested at the CERN Gamma Irradiation Facility and it shows the expected behaviour.