Quality Control of Micromegas Detectors for the ATLAS New Small Wheel Upgrade Project and Optimization of the Spatial Resolution of PoSSuMuS Detectors in two Dimensions

Micro Mesh Gaseous Structure Detectors (Micromegas) are planar gaseous tracking detec- tors for charged particles. This detector consists of three planar and parallel structures, a copper cathode, stainless steel micro-mesh and a segmented readout anode. Due to their high rate capability, their precise position reconstruction better than 100 µm and the possi- bility to build them with a square meter size active area they will be part of the upgrade of the inner end cap of the ATLAS forward muon spectrometer. In Munich the 2 m2 sized so called SM2 module is constructed and assembled. In order to provide the mentioned spatial resolution the requirements imposed on the detector components are high, like a planarity with a RMS of below 30 µm over the full active area and a parallelism of the anode readout strips of better than 20µm m . This thesis covers the construction procedure of the SM2 modules to meet the requirements as well as a presentation of methods to perform quality control measurements of the men- tioned requirements. The planarity is measured with a laser triangulation distance sensor. The topology measurement setup including this laser is better than 10 µm. With this setup the planarity of the investigated module is up to 14 µm over the full active area. These results show that the applied construction procedure can be used to build SM2 module ac- cording to the requirements. It was shown, that studying Micromegas in the Cosmic Ray Facility (CRF) allows also for a measurement of the planarity of the detector and of the strip alignment. This study was performed using a 1 m2 Micromegas, as long as no final assembled SM2 module exists. Dur- ing series production of the SM2 modules it is planned to calibrate all detectors with the CRF. In the second part a two dimensional position sensitive scintillating muon detector with sil- icon photomultiplier readout (PoSSuMuS) is studied with the aim of improving its spatial resolution to be better than 10 mm. It is planned to upgrade the CRF with the imple- mentation of a selection tool for high energetic muons. Such muons get less deflected by Coulomb interactions when passing matter. All measurements in the CRF are performed by comparing the track of a cosmic muon in the reference chambers to the tracklet in the detector under investigation. Those reference detectors of the CRF are Monitored Drift Tube (MDT) chambers consisting of aluminum tubes. The tracks of low energetic muons can get highly deflected when traversing those aluminum tubes as well as the Micromegas distorting the resolution of the CRF. Comparing the reference track to the position of the muon reconstructed with PoSSuMuS after traversing a layer of 300 mm iron gives a way to determine the energy of the particle. PoSSuMuS is a modular detector with each module consisting of two optical isolated trape- zoidal scintillator rods with a silicon photomultiplier (SiPM) readout on both sides of the rods. Scintillation light is gathered and by wavelength shifting fibers and guided to the ends of the rods. The first coordinate of PoSSuMuS along the rods is determined by the propagation time of the scintillation light towards both readouts. For the second coordinate perpendicular to the rods the light yield of both trapezoids is compared. The spatial reso- lution of the current design of PoSSuMuS is limited by the photon detection efficiency. A simulation of the setup showed, that by reducing the height of the trapezoid, optimizing the fiber position and increasing the fiber volume, the photon count per event can be drastically increased and with this also the spatial resolution. In a test beam at CERN with 120 GeV muons and Micromegas as reference detectors four trapezoidal geometries with a height of 50 mm and length of 100 mm and 300 mm are in- vestigated. The result for the best performing geometry allowed for 5 mm spatial resolution from the relative light yield in the two trapezoidal scintillators and for 90 mm spatial reso- lution from the difference in light propagation time. This is a result of an improved photon detection efficiency showing up to 150 photons in a SiPM per event. The aim of enhancing the light yield and improving the spatial resolution to below 10 mm is reached.