Study of Event Topology for a new Fast Primary Vertex Finder for the ATLAS Trigger

This document presents a transform-based approach to primary vertex finding and a feasibility analysis. The feasibility analysis first shows theoretical distinguishability of different signal events and pileup with a metric devised for this purpose. The results show high distinguishability for the majority of event types with expectedly low distinguishability for special cases. The algorithm is intended for use in the high level trigger. At this stage of computation, event types can be distinguished through the trigger, allowing choosing this algorithm only for appropriate events. An implementation of the algorithm with different increasingly realistic settings shows the impact of the different factors on efficiency. With realistic settings, distinguishability only reduces by a small margin, remaining for applicable events between 95% and 100% depending on the scenario. By gradually increasing the degree of realism of the setting, efficient countermeasures could be devised for different problems, which are also presented.