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The silicon vertex detector (SVD) is a four-layer double-sided strip detector installed at the heart of the Belle II experiment, taking data at the high-luminosity B -Factory SuperKEKB since 2019. SVD has been operating smoothly and reliably, showing a stable and above-99% hit efficiency, and a large signal-to-noise ratio in all sensors. In June 2022 the data-taking of the Belle II experiment was stopped for the Long Shutdown 1, primarily required to complete the vertex detector (VXD) with the inner two-layer DEPFET detector and to upgrade several components of the accelerator. This article reports on the excellent performance of SVD in terms of the signal-to-noise ratio, the hit position resolution, as well as the hit-time resolution. We briefly describe the challenges and delicate phases of the VXD re-installation and the SVD status for operation starting in early 2024. In SVD layer 3, which is closest to the interaction point, the average occupancy has been less 0.5%, well below the estimated limit for acceptable tracking performance. However, higher machine backgrounds are expected at increased luminosity, and so also increased hit occupancy. To enhance the robustness of offline software in a high-background environment, new algorithms of background suppression using the excellent SVD hit-time information have been developed, which allows a significant reduction of the fake rate, while preserving the tracking efficiency. With the increasing luminosity also the radiation levels are expected to increase, with possible deterioration of the sensor performance. The SVD integrated dose is estimated by the correlation of the SVD occupancy with the dose rate measured by the diamonds of the radiation monitor and beam-abort system. The effects of radiation damage are starting and in good agreement with our expectations. So far, no harmful impact due to the radiation damage on the detector performance has been observed. [ABSTRACT FROM AUTHOR]

The Belle II experiment located at KEK, Japan takes data from asymmetric e + e − collision provided by the SuperKEKB accelerator. The Silicon Vertex Detector (SVD), which is part of the Belle II Vertex Detector (VXD), has been operating smoothly and reliably since the start of data taking in March 2019. In this article, we report on the performance of the SVD in terms of the large signal-to-noise ratio, the good hit position resolution as well as the good hit-time resolution. New algorithms based on hit-time information are under development to improve robustness of tracking performance within the anticipated high background environment. The Background situation of the SVD has been constantly monitored and no degradation in performance is observed so far. To investigate the SVD performance at high luminosity runs in the future, simulation as well as an irradiation campaign are launched and their results are summarized. During the first long shutdown of the Belle II experiment, which starts from June 2022, the VXD has been refurbished with a new two-layer DEPFET pixel detector located inside the SVD. All the delicate phases of the disassembly, re-assembly and installation of the new VXD have been successfully completed. The new VXD commissioning phase began in Sept 2023 to get ready for beam operation starting in early 2024. [ABSTRACT FROM AUTHOR]

The Belle II experiment is taking data at the asymmetric SuperKEKB collider (KEK, Japan), which operates at the Υ (4 S) resonance. The vertex detector is composed of an inner two-layer pixel detector (PXD) and the silicon vertex detector (SVD), made of four layers of double-sided silicon strip detectors. A deep knowledge of the system has been gained since the start of operations in 2019 by assessing the high-quality and stable reconstruction performance of the detector. The very high hit efficiency and large signal-to-noise ratio are monitored via online data-quality plots. The good cluster-position resolution is estimated using the unbiased residual with respect to the track, and it is in reasonable agreement with the expectations. The SVD dose is estimated by the correlation of the SVD occupancy with the dose measured by the diamond sensors of the radiation-monitoring and beam-abort system. First radiation damage effects are measured on the sensor current and strip noise are shown not to affect the performance. Six samples of the shaped particle signal are recorded utilizing the multi-peak mode of the APV25 front-end chip and used to determine the hit timing with a precision of 2 to 3 ns. Recently a method to compute the time of collision from SVD hit time information has been implemented and verified with simulations and on data. [ABSTRACT FROM AUTHOR]

The Silicon Vertex Detector (SVD) is a part of the vertex detector in the Belle II experiment at the SuperKEKB collider (KEK, Japan). Since the start of data taking in spring 2019, the SVD has been operating stably and reliably with a high signal-to-noise ratio and hit efficiency, achieving good spatial resolution and high track reconstruction efficiency. The hit occupancy, which mostly comes from the beam-related background, is currently about 0.5% in the innermost layer, causing no impact on the SVD performance. In anticipation of the operation at higher luminosity in the following years, two strategies to sustain the tracking performance in future high beam background conditions have been developed and tested on data. One is to reduce the number of signal waveform samples to decrease dead time, data size, and occupancy. The other is to utilize the good hit-time resolution to reject the beam background hits. We also measured the radiation effects on the full depletion voltage, sensor current, and strip noise caused during the first two and a half years of operation. The results show no detrimental effect on the SVD performance. [ABSTRACT FROM AUTHOR]