The luminosity increase at the LHC in Phase-II calls for an in-depth redesign of the Monitored
Drift Tube (MDT) chamber readout. One reason for this is the high rate of primary detector
signals which requires increased readout bandwidth all along the data path. The second reason is
due to a new concept for the formation of the Level-1 muon trigger (L1), which aims to improve
the selectivity for muons with high transverse momentum (p T ). While in the present system the
L1 trigger is exclusively based on specialized trigger chambers (RPC in the barrel, TGC in the
endcap), which deliver tracking information with very limited accuracy, the L1 trigger will, in
Phase-II, also consider tracking information from the MDT: the time resolution of the trigger
chambers, able to tag the beam crossing (BX), will be combined with the high spatial accuracy of
the MDT.
In the new L1 trigger scheme, the selection of MDT hits corresponding to a given BX, will be
based on a Region of Interest (RoI) provided by the trigger chambers. Considering only MDT
hits in the RoI will result in a large reduction of the relevant data volume. The selected MDT hits
will be tested for consistency with the track direction, as defined by the RoI. If confirmed, the
MDT hits are used for a better p T definition.
The rate of background hits from γ and neutron conversions is several orders of magnitude higher
than the one from muon hits. The selection of muons against this background ("hit extraction")
requires high-speed processing power, capable to supply the relevant information to the Muon
Central Trigger Processor (MUCTPI) inside the latency of 10 μs.