Tracking for the ATLAS Level 1 Trigger for the HL-LHC

At the HL-LHC, the increased luminosity will result in up to 200 pile-up interactions per bunch crossing. One of the greatest challenges for ATLAS will be to keep the Level-1 Trigger pT thresholds low enough in order to keep high trigger efficiency for all the interesting physics. We describe the proposed two-stage design of the ATLAS Level-1 Trigger and how a Level-1 track trigger fits in this design, the requirements and implications for the tracker readout architecture, and estimates of readout bandwidth and latency based on a detailed discrete event simulation of the data flow on the tracker front-end electronics.