Particle Tracking with Micro-Pattern Gaseous Detectors

GEM and micromegas detectors are Micro-Pattern Gaseous Detectors (MPGDs). They are intrinsi- cally high-rate capable and show excellent spatial resolution due to small drift lengths and high read-out granularity. Large micromegas detectors will replace parts of the forward high-precision muon tracking system of the ATLAS detector, which will be able to cope with the increased back- ground when the Large Hadron Collider will exceed its current luminosity of 2 × 1034 cm−2 s−1 after 2020. The full tracking potential of these detectors cannot be reached by standard read-out and reconstruction techniques. In this thesis different novel approaches are discussed and introduced, which allow a distinct enhancement in position information. This is achieved by employing methods that take into account the full track information of a charged particle in the detector. In thin planar GEM and micromegas detectors particle tracking is performed by utilization of a time resolving read-out, which allows a Time-Projection-Chamber-like (TPC) track reconstruction for several applications. Thermal neutrons are detected with high precision by reconstructing the tracks of ions emerging from a neutron capture process in a thin 10B conversion layer. The method is tested in a thermal neutron beam of 3.7 meV with a 10 cm × 10 cm GEM detector. Thereby a reconstruction efficiency of 5 % in a 2 µm boron conversion layer and a spatial resolution of (100 ± 10) µm is achieved. From this a similar method is derived for the usage in Thick-GEM detectors (TGEM), which results in an enhanced spatial resolution as well. This is tested through the tracking of 5 MeV alpha particles. For these a spatial resolution of (360 ± 30) µm is reached. An alternative reconstruction method for tracking of minimal ionizing particles in multiple detector layers allows for a significantly enhanced position determination for small GEM-detectors. For muons of 10–150 GeV a spatial resolution below 150 µm is obtained independent of the track inclination. A model for strip cross-talk is developed and a compensating method is applied, which allows improved track inclination reconstruction in a single detector layer. In this thesis the construction of micromegas detectors for the ATLAS muon spectrometer upgrade is described. Furthermore a 2 m2 prototype with four layers is tested in a 10–150 GeV muon beam. The pulse height, efficiency and spatial and timing resolution of the quadruplet are determined and the general suitability for triggering on this type of detector is studied. Perpendic- ularly incident muons are reconstructed with a spatial resolution below 100 µm and an efficiency above 95 %. With a modified tracking technique and by application of a timing compensation a considerably improved spatial resolution of 200 µm is obtained for inclinations of 20◦ and 30◦ at high reconstruction efficiency of 97 %. The capability of GEM-detectors for beam monitoring or ion radiography under very high rates is evaluated in a carbon ion beam with particle fluxes between 2–50 MHz. The separation of single particles and the spatial resolution depending on the particle flux is studied. Single particles are resolved with good spatial resolution even at the highest rates, when in average eight particles are traversing the detector simultaneously.