Upgrading the ATLAS Level-1 Calorimeter Trigger using Topological Information

The ATLAS Level-1 Calorimeter Trigger (L1Calo) is a fixed latency, hardware-based pipelined system designed for operation at the LHC design luminosity of 10^34cm-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.