Test-beam results & performance studies of the ATLAS Micromegas production modules

The LHC at CERN plans to have a series of upgrades to increase its instantaneous luminosity to 7.5×10$^{34} cm^{−2}s^{−1}$. The ATLAS experiment will upgrade its inner end-cap muon chambers to cope with the increased collision rate expected from the High-Luminosity-LHC. This project, called New Small Wheel, includes resistive Micromegas chambers together with small-strip Thin Gap Chambers (sTGC), conforming a system of ~2.4 million readout channels in total. This is the first time that large Micromegas are built in such a scale. In total, 128 Micromegas modules up to 3 m$^2$ in size, and from different production sites spread in Europe, will be produced, with target installation at the end of Long Shutdown 2 (LS2) of the LHC. One of the first series modules, equipped with a prototype of the final front-end electronics based on VMM chip, was tested in muon/pion beam at the H8 line of SPS at CERN during the summer of 2018. We present the test setup and performance results on efficiency and resolution for perpendicular and inclined tracks. These studies were focused on determining the working point of the ATLAS Micromegas detectors. Results are also compared with the initial requirements for operation in ATLAS, namely spatial resolution of 100 μm at high background hit rate of up to 20 kHz/cm2. Studies with several gas mixtures were also carried out and will be presented.