Performance of Large Area Micromegas Detectors for the ATLAS Muon Spectrometer Upgrade Project

Four German institutes are building 32 high-rate capable SM2 Micromegas quadruplets, for the upgrade of the Small Wheels of the ATLAS muon spectrometer. The cathodes and strip-anodes of the 2 m$^2$ quadruplets consist of stable honeycomb sandwiches with a requested planarity better than 80 $\mu$m. The qualification of full-size SM2 quadruplets will be performed in the Munich Cosmic Ray Measurement Facility (CRMF). Two fully working 4 m $\times$ 2.2 m ATLAS drift-tube chambers provide muon tracking, a RD51 SRS based data acquisition system provides readout of all 12288 electronic channels using 96 APV25 front-end boards. The goal is to measure the homogeneity of pulse-height and efficiency and to determine the planarity of the sandwich planes and the positions of the readout-strips. This has been pioneered by studying a 102 $\times$ 92 cm$^2$ Micromegas chamber with similar readout pitch in the CRMF using the TPC-like analysis method. At trigger rates above 100 Hz data taking takes only a few days for sufficient statistics. Shifts of readout planes and bulging due to overpressure were resolved with an accuracy better 50$\mu$m, single plane angular resolution with an accuracy of about 5$^\circ$ and spatial resolution of 300 $\mu$m in agreement with 83 $\mu$m for the same detector at high energy 120 GeV pion beams taking into account the multiple scattering of the low energy cosmic muons.