A Method for a Level 2 Muon Trigger for ATLAS.

A method for a level 2 trigger for the ATLAS muon system in the region 0 < eta 2 is described. The methodd is based on pattern recognition in both the triggerand monitored drift tube chambers and a reconstruction algorithm for the MDT system.The MDT pattern recognition algorithm uses a type of Hough tranform to measurethe adjacency of candidate tracks and a chi-squared test to select and refine MDT candidate tracks. The trigger momentum is estimated by comparing the radius ofcurvature for the reconstructed MDT track within a trigger road with a linear interpolationof nearly mathcing tracks read from a fast lookup table. The performance of the algorithm under a random noise background is simulated. Resolutions of order5% and 10% by Gaussian fits are achieved for 20 GeV and 6 GeV Pt muon tracksrespectively with an overall reconstruction efficiency of > 97%.