Study of the performance of the MicroMegas chambers for the ATLAS muon spectrometer upgrade

Micromegas is one of the detector technologies (along with the TGC Thin Gap Chambers) that has been chosen for precision tracking and trigger capabilities for the upgrade of the forw ard muon detectors of the ATLAS experiment, covering an area of more than 1200 m2. The chambers have been designed to allow operation in a high rate environment, to guarantee a resolution below 100μm per point on a large area and to provide a fast trigger signal. In the last months several tests have been done on small area prototypes in order to verify that the requirements on resolution and rate capabilities are well matched. In parallel, a particular effort has been devoted to develop construction procedures for large area chambers able to guarantee the required precision properties. We present the results of the performance studies done on beams at CERN and in other laboratories. Track reconstruction is performed using the charge centroid and the μ TPC method. Results include space and angular resolution for perpendicular and inclined tracks, efficiency and time resolution. Performances in magnetic field have been also studied in dedicated test beams, and the behavior of the detector has been compared to simulations. Finally an overview of the detector performance after neutron, X ray, γ and α exposure, is also presented.