The new two-layer Belle II PiXel Detector

Abstract The Belle II experiment [1] at SuperKEKB [2] has been collecting data from asymmetric-energy e + e - collisions at the Υ(4S) resonance at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan, since 2019. Its goal is to collect a BB̅ data set 50 times larger than those of its predecessors, Belle and BaBar, enabling unprecedented precision in the measurement of Standard Model processes and the search for new physics at the luminosity frontier. To achieve this, a vertex resolution on the order of 30 μm is required for precise discrimination of decay vertices and lifetime measurements of short-lived particles. This precision is achieved by the Belle II VerteX Detector (VXD), which consists of the ultra-low-mass PiXel Detector (PXD) based on DEpleted P-channel Field Effect Transistor (DEPFET) technology [3], surrounded by a double-sided silicon strip detector (SVD) [4]. A partially equipped PXD used for data taking period until 2022 (Run 1) has been replaced in 2023 by a new fully populated PXD. This PXD is used for the current data taking period (Run 2), which started in 2024. This article summarizes the commissioning and the first operation experience of the newly installed PXD.