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

The increased luminosity of the HL-LHC requires a new, high rate capa- ble, high resolution detector 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 squaremeter-sized micromegas quadruplets. This large size requires a sophisticated constructi- on to provide a spatial resolution better than 100 μm. The first series SM2 modules were investigated using 120 GeV pions and muons at SPS/CERN as well as with cosmic muons in a precision facility. During the testbeam in August 2017 at the H8 beamline of the SPS 4 small size micropattern detectors were used as tracking reference. The spatial reso- lution 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 time projection chamber like approach, the so-called μTPC method, yields a si- milar resolution for tracks inclined to the active area of the module. To investigate and calibrate the full active area of SM2 quadruplets a Cos- mic Ray Facility (CRF) is used. It uses two ATLAS Monitored Drift Tube chambers (MDT) to provide precise muon track information in the order of 100 μm. A segmented trigger hodoscope provides additional position in- formation in the order of 10 cm along the wires of the MDTs. The angular acceptance of the CRF is between −30 degree and +30 degree to the zenith angle over an area of about 8 squaremeter . We present results for the first series SM2 quadruplets with 12288 channels read out fully by 96 APVs connected to six FEC cards. A segmentation of the active area into smaller partitions enables a detailed analysis of local de- tector properties, for example geometrical quality, homogeneity in efficiency, in pulse height and in spatial resolution.