Abstract
A new CMS Tracker is under development for operation at the High Luminosity LHC from 2025. It includes an outer tracker based on special modules of two different types which will construct track stubs using spatially coincident clusters in two closely spaced sensor layers, to reject low transverse momentum track hits and reduce the data volume before data transmission to the Level-1 trigger. The tracker data will be used to reconstruct track segments in dedicated processors before onward transmission to other trigger processors which will combine tracker information with data originating from the calorimeter and muon detectors, to make the final L1 trigger decision. The architecture for processing the tracker data outside the detector is under study, using several alternative approaches. One attractive possibility is to exploit a Time Multiplexed design similar to the one which is currently being implemented in the CMS calorimeter trigger as part of the Phase I trigger upgrade. The novel Time Multiplexed Trigger concept is explained, the potential benefits for processing future tracker data are described and a feasible design based on currently existing hardware is outlined.
Highlights
A major upgrade of the CMS experiment at the CERN Large Hadron Collider is being planned so that the accelerator can deliver an integrated luminosity of 3000 fbÀ1 over a period of about a decade of operation for a physics programme which will include precision measurements of the newly discovered Higgs boson, further searches for new physics extended to higher masses, and for possible discrepancies with the standard model.The High Luminosity LHC will require a new tracker after 2023 because of gradual deterioration of the present detector due to accumulated radiation damage
Its replacement must satisfy several demanding requirements, including a lower material budget and increased granularity compared to the present detector, and enhanced radiation tolerance combined with tolerable power consumption and affordable cost
In the 2S-module [5,6], which is the most advanced, two silicon microstrip sensors are separated by a few mm, with the spacing determined by a compromise between transverse momentum precision and the fake stub rate resulting from combinatorial background caused by hits from nearby tracks, secondary interactions and photon conversions, for example
Summary
A major upgrade of the CMS experiment at the CERN Large Hadron Collider is being planned so that the accelerator can deliver an integrated luminosity of 3000 fbÀ1 over a period of about a decade of operation for a physics programme which will include precision measurements of the newly discovered Higgs boson, further searches for new physics extended to higher masses, and for possible discrepancies with the standard model. In the TMT all data from a given LHC bunch crossing (BX) arrive at a single node for processing, which minimises boundaries and data sharing between processors This still permits subdivision of the detector into regions, which is essential for such a large system as the tracker, but the division is a choice, rather than a constraint. Provided data are only shared between a maximum of two regions, a convention of accepting only candidates from a “left” or “right” region when data originate from both regions can simplify this task, so the layouts under consideration incorporate this constraint Another TMT advantage is that a very small number of nodes is needed to validate an entire trigger, since each main processor is carrying out identical processing, just delayed by one LHC clock cycle compared to its neighbour in a round robin fashion. If a hardware fault occurs at one TMT processor or its links, a redundant node can be quickly switched in by software to replace the faulty one
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