A Demonstrator for the ATLAS Level-1 Muon to Central Trigger Processor Interface (MUCTPI)

The Level-1 Muon Trigger Interface (MUCTPI) to the Central Trigger Processor (CTP) receives trigger information from the detector-specific logic of the muon trigger. This information contains up to two muon-track candidates per sector. The MUCTPI combines the information of all sectors and calculates total multiplicity values for each of six programmable pT thresholds. It avoids double counting of single muons by taking into account the fact that some of the trigger sectors overlap. The MUCTPI sends the multiplicity values to the CTP which takes the final Level-1 decision. For every Level-1 Accept (L1A) the MUCTPI sends region-of-interest (RoI) information to the Level-2 trigger and event data to the data acquisition system. A demonstrator of the MUCTPI has been built which has the performance of the final system but has limited flexibility for calculating the overlap. The functionality and the performance of the demonstrator are presented. I. MUON TRIGGER SYSTEM The ATLAS Level-1 trigger [1] is based on multiplicity information from clusters found in the calorimeters and from tracks found in dedicated muon trigger detectors. The muon trigger detector uses resistive plate chambers (RPCs) in the barrel region and thin-gap chambers (TGCs) in the end-cap and forward region. Coincidences of hits in different layers are used to identify muon-track candidates. The width of the roads used to define the coincidences determines the trigger transverse-momentum threshold of the candidates. Candidates are counted for six different programmable pT thresholds. An overview of the ATLAS muon trigger is shown in figure 1. Figure 1: ATLAS Level-1 Muon Trigger The trigger detectors are segmented into sectors. Each sector can identify up to two muon-track candidates in a total of six programmable pT thresholds. Detector-specific sector logic sends details of the two highest-pT candidates in each sector to the MUCTPI [2] which evaluates detector-wide multiplicities. Special attention is paid to muons that traverse overlapping trigger chambers [3]. In particular, within the barrel, and between the barrel and the end-cap regions, muon-track candidates could be counted twice. This would lead to an unacceptable rate of fake di-muon triggers. Overlap within sectors and between endcap and forward sectors is handled by the detectorspecific logic. There is no overlap between different octants in φ. The overlapping of sectors for one octant in φ is shown in figure 2. Figure 2: Overlap of Muon Trigger Sectors in one Octant The MUCTPI sends the total multiplicity values for the six programmable pT thresholds to the CTP which takes the Level1 decision. An overview of the muon trigger system is shown in figure 3. Figure 3: Muon Trigger System Overview low p T