Contribution Oral presentation
DEPFET at Belle II
The innermost detector of the Belle II experiment makes use of the DEPFET technology to provide the accurate position measurements that are needed for the reconstruction of B-meson decay vertices. This technology combines signal detection and amplification in a single silicon pixel structure, so that the position measurement of traversing particles can be achieved with an overall material budget of 0.075% radiation length, corresponding to 75 μm² in order to minimize the impact of multiple scattering for low transverse momentum tracking. Moreover, the DEPEFT detector has an excellent signal-to-noise ratio, low power consumption and offers a non-destructive readout. The instantaneous luminosity of 8x10³⁵ cm⁻²s⁻¹ expected at SuperKEKB increases the event rate and causes a large background. The close proximity of the pixel detector to the beampipe (only 1.4 cm from the interaction point) poses many challenges to the detector technology, in particular to radiation hardness and electronics. The vertex pixel detector consists of two DEPFET layers (radii at 14 mm and 22 mm). These are 20 ladders in total corresponding to 8 Mega Pixels (pixel sizes: 50x55 μm² and 50x75 μm²). The four-fold readout in rolling shutter mode results in a total readout time of about 20 μs for an entire frame. The concept of the sensor and the surrounding readout electronics will be presented in detail with focus on the Belle II experiment. 17 institutes from Europe and Asia work together in the DEPFET collaboration to meet these challenges.