High resolution DEPFET active pixel sensors for the Belle II experiment

The new Belle II experiment at the SuperKEKB collider at KEK was launched in 2009 as a general upgrade of the previous successful Belle experiment. Important improvements in the Belle II detector are additional two pixel layers forming the innermost part of the vertex detector. This paper gives a short overview of the expected impact of the two inner pixel layers on the performance of Belle II based on simulations and current experimental knowledge of the DEPFET pixel detectors. The focus is on the expected performance of the thinned DEPFET pixel sensors in Belle II in terms of spatial resolution. The measurements and simulations of the current generation of DEPFET sensors in beam tests indicate that the design resolution requirements can be met. The dependence of the spatial resolution on the deposited energy was observed in beam tests and we simulated the effect for the Belle II detector type to estimate its magnitude. A short description of the readout and data acquisition chain of the Belle II pixel vertex detector is given.