Study of ionization, amplification and energy resolution in GridPix detectors

In our group there are several gaseous detectors in development based on a highly granular pixel ASIC (Timepix) and a MicroMegas gas amplification stage (InGrid). The MicroMegas is produced by photolithographic postprocessing techniques and can be aligned with the pixel structure so that one grid hole is directly above one pixel. The combination of the Timepix ASIC and the InGrid amplification stage is then called "GridPix". Such GridPix detectors can be used for several different applications like tracking in a TPC (for instance ILD TPC) or for detection of X-ray photons (for instance at CAST or IAXO). The advantage of such a setup is its low capacitance and thus low noise which leads to the possibility of single primary electron detection. For improving future GridPix detectors like the IAXO detector it is important to understand and quantify all detection processes. The detection of single primary electrons was used for studies of the processes in the conversion and in the amplification region of a GridPix X-ray detector with the detection of low energetic X-ray photons. In the talk I present measurements and results regarding the ionization, the amplification and the energy resolution. Furthermore I present estimations of the Fano factor and the Penning transfer efficiencies in argon isobutane mixtures based on these measurements and corresponding Garfield++ simulations.