Improvement of the L1 trigger for the ATLAS muon spectrometer at high luminosity

When the peak luminosity of 10 34 cm − 2 s − 1 of the LHC will be increased by a factor of 5–7 in about a decade from now (“SLHC”), the selectivity of the ATLAS Level-1 (L1) triggering system will have to be improved in order to cope with the maximum allowed trigger rate of about 100 kHz. For the L1 trigger of the ATLAS Muon Spectrometer this calls for an increase of the pT-threshold for single muons. In the present L1 muon trigger system, however, the effective pT-threshold is not very sharp due to the limited spatial resolution of the trigger chambers, resulting in a majority of L1 triggers from muons below threshold. We describe a new, high-speed readout system of the Monitored Drift Tube chambers, which allows to supply the precision coordinates of the candidate muon to the L1 trigger, resulting in an accurate momentum determination, a sharpened pT-threshold and an efficient rejection of unwanted L1 triggers from low-pT muons.