Vertex Reconstruction and Tracking in the Trigger Algorithm for Atlas

Online track and vertex reconstruction are fundamental ingredients for event selection at Large Hadron Collider (LHC) experiments. In the ATLAS experiment the first reconstruction stage where this goal will be achievable is the software-based Second Level Trigger (LVL2). In this contribution we present algorithms for fast reconstruction of charged tracks and of secondary vertexes in the framework of the ATLAS High Level Trigger (HLT). Trigger tools for track fitting and extrapolation are also described. Examples of performance evaluation methods adopted to characterise the presented algorithms are given, along with results obtained on simulated and real data. Efficient and robust tracking capabilities are demonstrated to be achievable with average execution times in agreement with the trigger requirements.