Development and construction of the Belle II DEPFET pixel detector

Abstract

The construction of the new accelerator at the Japanese Flavour Factory (KEKB) has been finalized and the commissioning of its detector (Belle~II) is planned by early 2017. This new e$^{+}$e$^{-}$ machine (SuperKEKB) will deliver an instantaneous luminosity of $8\times10^{35}\mathrm{~cm}^{-2}\mathrm{s}^{-1}$, which is 40 times higher than the world record set by KEKB. In order to be able to fully exploit the increased number of events and provide high precision measurements of the decay vertex of the B meson systems in such a harsh environment, the Belle~II detector will include a new silicon vertex detector, based on the DEPFET technology. The new pixel detector, located close to the interaction point, consists of two layers of active pixel sensors. The DEPFET technology combines the detection and the in-pixel amplification by the integration, on every pixel, of a field effect transistor into a fully depleted silicon bulk. In Belle~II, DEPFET sensors thinned down to 75~$\mu$m with low power consumption and low intrinsic noise will be used. In this paper, an overview of the latest results and the construction status are presented. Properties of small prototype matrices operated with close to final readout ASIC electronics have been characterized. In particular results from a combined test beam with full-size matrices are described.