Abstract
The ATLAS Level-1 Calorimeter Trigger (L1Calo) is a fixed latency, hardware-based pipelined system designed for operation at the LHC design luminosity of 1034cm−2s−1. Plans for a several-fold luminosity upgrade will necessitate a complete replacement for L1Calo (Phase II). But backgrounds at or near design luminosity may also require incremental upgrades to the current L1Calo system (Phase I). This paper describes a proposed upgrade to the existing L1Calo to add topological algorithm capabilities, using Region of Interest (RoI) information currently produced by the Jet and EM/Hadron algorithm processors but not used in the Level-1 real-time data path.
Highlights
The ATLAS Level-1 Calorimeter Trigger (L1Calo) is a fixed latency, hardware-based pipelined system designed for operation at the LHC design luminosity of 1034cm−2s−1
A topological processor (TP) performing more sophisticated algorithms on the combined feature set and sending results to CTP can be added at later stage
The current common merger” module (CMM) module [3] processes the results from the Cluster Processor Modules (CPMs) or Jet/Energy Modules (JEMs) modules to produce results over the entire crate, and send them to a “system” CMM in order to produce system-wide results
Summary
The present trigger capabilities allow to make selections on counts of objects of various types (for example 2 jets > 40 GeV), and even separate counts of objects (eg MET > 50 GeV && 2 jets > 40 GeV). There is presently no provision for spatial correlation of different objects, or for differentiating jets and em/tau clusters identified in the different subsystems but originating from the same energy deposits. A possible solution could be to include jet/cluster position information (RoI) in the real time data path (in the current system it is available only for the DAQ system) and to use this information to add topology-based algorithms at Level 1. Identification of spatial overlap between e/tau clusters and jets, usage of the local jet Et sum to estimate energy of overlapping e/tau objects and calculation of invariant transverse mass would be possible. Some of them require only local information, others need global information
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