Calibration of ultra-thin hybrid pixel detector assemblies with Timepix readout ASICs

In the framework of vertex detector R&D for a future Compact Linear Collider, the charac- terisation of ultra-thin hybrid pixel detector assemblies comprising 50 − 300 μm thick silicon sensors and Timepix readout ASICs is underway through beam tests at DESY and CERN. The work presented here supports the beam test data analysis by providing an energy calibra- tion of certain assemblies, so giving access to energy measurements in addition to recorded Time Over Threshold counts. Photons from a variety of radioactive sources and X-ray fluorescence are used to measure the response of the assemblies in the region of 3 − 60 keV. Threshold measurements are also performed. Global and pixel-by-pixel calibrations of the assemblies are parametrised and the uniformity of the response of the pixel matrices are discussed. Data samples recorded in beam tests are calibrated and the resulting energy spectra presented. For the first time calibration parameters are estimated for two 50 μm thick sensors which are foreseen as a candidate technology for the CLIC vertex detector.