Preliminary performance studies for the ATLAS Muon Trigger during initial Run 2

The physics program of the ATLAS experiment at CERN's Large Hadron Collider (LHC) includes the search for the Higgs Boson and the measurements of its properties, searches for new physics and precision measurements of the Standard Model. Events with high momentum muons in the final state are an important signature of many of these physics topics, then an efficient muon trigger and a deep understanding of its performance are crucial. During Run 1 the ATLAS muon trigger was successfully adapted to the challenging environment, thus reaching an excellent performance. During Run 2 ~100 pb-1 of data with 50 ns bunch spacing have been already collected, while the collection of data with 25 ns bunch spacing is currently ongoing. As the data taking proceeds, the muon trigger performance is being constantly monitored. The muon trigger efficiency, studied both with respect to offline muon reconstruction and with Tag&Probe method applied to the Z decays in muon pairs, is presented here as a function of different kinematic variables for various trigger items. The muon trigger scale factors, needed by all physics analyses using muons to normalize Monte Carlo simulations according to data, are also shown. Presented results are obtained using Monte Carlo and so far collected collision data for both 50 and 25 ns bunch spacing.