Performance and Calibration of 2m^2-sized 4-layered Micromegas Detectors for the ATLAS Upgrade

The increased luminosity of the HL-LHC requires a new, high rate capable, high resolution detec- tor technology for the inner end cap of the muon spectrometer of the ATLAS experiment. For this purpose the Micromegas technology is chosen as precision tracker. The SM2 modules are 2 m^2 - sized Micromegas quadruplets and cover about 25% of the active Micromegas area of the New Small Wheels. This large size requires a sophisticated construction to provide a spatial resolution better than 100 μm. The first prototype SM2 module was investigated using 120 GeV pions and muons at SPS/CERN as well as with cosmic muons in a precision facility. The spatial resolution of the SM2 detector is analyzed using two different methods. A charge weighted position reconstruction, the so-called centroid method, achieves a spatial resolution of about 80 μm for perpendicular particle incident. A drift time evaluation of the strip readout, yields a similar resolution for tracks inclined to the active area of the module. To investigate and calibrate the full active area of SM2 quadruplets the LMU Cosmic Ray Facility (CRF) is used. Two ATLAS Monitored Drift Tube chambers (MDT) provide precise muon track information in the order of 100 μm. A trigger hodoscope segments the position information in 10 cm bands along the wires of the MDTs. The angular acceptance of the CRF is between -30 and +30 degree to the zenith angle over an area of about 8 m^2 . We present results for the first prototype SM2 quadruplet with 12288 channels read out fully by 96 APVs connected to six FEC cards. The segmentation of the active area enables a detailed analysis of local detector properties, for example geometrical quality, homogeneity in efficiency, in pulse height and in spatial resolution.