A muon trigger algorithm for Level-2 feature extraction

An algorithm is presented to perform muon trigger extraction on MuonSpectrometer data in the barrel region, as part of the ATLAS Level-2 trigger. This algorithm is designed to be both conceptually simple and fast so as to readily be implemented in the demanding online environment in which the ATLAS Level-2 code will run. The algorithm confirms Level-1 muon triggers with a precise muon momentum measurement, and rejects fake Level-1 trigger induced by physics background. The performance of the algorithm has been confirmed by studies of background in the Muon Spectrometer. This has entailed the development of a novel technique to add a realistic simulation of background hits from overlapping events to prompt muon data. Both the performance and timing of the algorithm are seen to be robust in the presence of such background. The code has been developed in C++ and integrated into the ATLAS ATRIG trigger simulation framework.