Performance studies of resistive Micromegas detectors for the upgrade of the ATLAS Muon Spectrometer

Resistive Micromegas (Micro MEsh Gaseous Structure) detectors have proven along the years to be a reliable high rate capable detector techno- logy characterised by an excellent spatial resolution. The ATLAS colla- boration at LHC has chosen the resistive Micromegas technology (mainly for tracking), along with the small-strip Thin Gap Chambers (sTGC, mainly for triggering), for the high luminosity upgrade of the inner muon station in the high-rapidity region, the so called New Small Wheel (NSW) upgrade project. The NSW requires fully efficient Micromegas chambers with spatial resolution better than 100μm independent of the track inci- dence angle and the magnetic field (B < 0.3 T), with a rate capability up to ∼ 10kHz/cm2. Along with the precise tracking the Micromegas chambers should be able to provide a trigger signal, complementary to the sTGC, thus a decent timing resolution is required. Several tests have been performed on small (10×10cm2) and medium size (1×0.5m2) resistive Micromegas chambers (bulk type and mechanical floating mesh type) using medium (10GeV/c) and high (150GeV/c) momentum hadron beams at CERN including measurements inside magnetic field. Results on the measured efficiency, position and timing resolution will be shown de- monstrating the excellent characteristics of the detectors that fulfil the NSW requirements. In addition, early test results from the first full size (2−3m2) operational modules that will be realised during 2015, will be presented.