The Belle II Silicon Vertex Detector

The KEKB machine and the Belle experiment in Tsukuba (Japan) are now undergoing an upgrade, leading to an ultimate luminosity of 8 10 35 cm − 2 s − 1 in order to measure rare decays in the B system with high statistics. The previous vertex detector cannot cope with this 40-fold increase of luminosity and thus needs to be replaced. Belle II will be equipped with a two-layer Pixel Detector surrounding the beam pipe, and four layers of double-sided silicon strip sensors at higher radii than the old detector. The Silicon Vertex Detector (SVD) will have a total sensitive area of 1 : 13 m 2 and 223,744 channels — twice as many as its predecessor. All silicon sensors will be made from 150 mm wafers in order to maximize their size and thus to reduce the relative contribution of the support structure. The forward part has slanted sensors of trapezoidal shape to improve the measurement precision and to minimize the amount of material as seen by particles from the vertex. Fast-shaping front-end ampli fi ers will be used in conjunction with an online hit time reconstruction algorithm in order to reduce the occupancy to the level of a few percent at most. A novel “ Origami ” chip-on-sensor scheme is used to minimize both the distance between strips and ampli fi er (thus reducing the electronic noise) as well as the overall material budget. This report gives an overview on the status of the Belle II SVD and its components, including sensors, front-end detector ladders, mechanics, cooling and the readout electronic

The Silicon Vertex Detector of the Belle II experiment

International audienceSince the start of data taking in spring 2019 at the SuperKEKB collider (KEK, Japan) the Belle II Silicon Vertex Detector (SVD) has been operating reliably and with high efficiency, while providing high quality data: high signal-to-noise ratio, greater than 99% hit efficiency, and precise spatial resolution. These attributes, combined with stability over time, result in good tracking efficiency. Currently the occupancy, dominated by beam-background hits, is quite low (about 0.5 % in the innermost layer), causing no problems to the SVD data reconstruction. In view of the operation at higher luminosity foreseen in the next years, specific strategies aiming to preserve the tracking performance have been developed and tested on data. The time stability of the trigger allows reducing sampling of the strip-amplifier waveform. The good hit-time resolution can be exploited to further improve the robustness against the higher level of beam background. First effects of radiation damage on strip noise, sensor currents and depletion voltage have been measured: they do not have any detrimental effect on the performance of the detector. Furthermore, no damage to the SVD is observed after sudden and intense bursts of radiation due to beam losses

Performance and running experience of the Belle II silicon vertex detector

International audienceThe Belle II silicon vertex detector is one of the vertex detectors in the Belle II experiment. The detector reads out the signals from the double-sided silicon strip sensors with the APV25 front-end readout ASIC, adopting the chip-on-sensor concept to minimize the strip noise. The detector has been operated in the experiment since the spring of 2019. Analyzing the acquired data during the beam collisions, the excellent performance of the detector is confirmed. Also, the radiation dose and 1-MeV equivalent neutron fluence of the detector are estimated using the measured dose rates of the diamond sensors installed on the beam pipe and are compared with the measured radiation effects in the strip noise, leakage current, and depletion voltage. This paper briefly introduces the main features of the silicon vertex detector, and then reports on the measured performance and radiation effects of the first two years of running experience of the detector

The Silicon Vertex Detector of the Belle II experiment

International audienceSince the start of data taking in spring 2019 at the SuperKEKB collider (KEK, Japan) the Belle II Silicon Vertex Detector (SVD) has been operating reliably and with high efficiency, while providing high quality data: high signal-to-noise ratio, greater than 99% hit efficiency, and precise spatial resolution. These attributes, combined with stability over time, result in good tracking efficiency. Currently the occupancy, dominated by beam-background hits, is quite low (about 0.5 % in the innermost layer), causing no problems to the SVD data reconstruction. In view of the operation at higher luminosity foreseen in the next years, specific strategies aiming to preserve the tracking performance have been developed and tested on data. The time stability of the trigger allows reducing sampling of the strip-amplifier waveform. The good hit-time resolution can be exploited to further improve the robustness against the higher level of beam background. First effects of radiation damage on strip noise, sensor currents and depletion voltage have been measured: they do not have any detrimental effect on the performance of the detector. Furthermore, no damage to the SVD is observed after sudden and intense bursts of radiation due to beam losses

Measurement of the cluster position resolution of the Belle II Silicon Vertex Detector

International audienceThe Silicon Vertex Detector (SVD), with its four double-sided silicon strip sensor layers, is one of the two vertex sub-detectors of Belle II operating at SuperKEKB collider (KEK, Japan). Since 2019 and the start of the data taking, the SVD has demonstrated a reliable and highly efficient operation, even running in an environment with harsh beam backgrounds that are induced by the world’s highest instantaneous luminosity. In order to provide the best quality track reconstruction with an efficient pattern recognition and track fit, and to correctly propagate the uncertainty on the hit’s position to the track parameters, it is crucial to precisely estimate the resolution of the cluster position measurement. Several methods for estimating the position resolution directly from the data will be discussed

The silicon vertex detector of the Belle II experiment

International audienceIn 2019 the Belle II experiment started data taking at the asymmetric SuperKEKB collider (KEK, Japan) operating at the Y(4S) resonance. Belle II will search for new physics beyond the standard model by collecting an integrated luminosity of 50 ab$^{−1}$. The silicon vertex detector (SVD), consisting of four layers of double-sided silicon strip sensors, is one of the two vertex sub-detectors. The SVD extrapolates the tracks to the inner pixel detector (PXD) with enough precision to correctly identify hits in the PXD belonging to the track. In addition the SVD has standalone tracking capability and utilizes ionization to enhance particle identification in the low momentum region. The SVD is operating reliably and with high efficiency, despite exposure to the harsh beam background of the highest peak-luminosity collider ever built. High signal-to-noise ratio and hit efficiency have been measured, as well as the spatial resolution; all these quantities show excellent stability over time. Data-simulation agreement on cluster properties has recently been improved through a careful tuning of the simulation. The precise hit-time resolution can be exploited to reject out-of-time hits induced by beam background, which will make the SVD more robust against higher levels of background. During the first three years of running, radiation damage effects on strip noise, sensor currents and depletion voltage have been observed, as well as some coupling capacitor failure due to intense radiation bursts. None of these effects cause significant degradation in the detector performance

The Silicon Vertex Detector of the Belle II Experiment

International audienceThe Belle II experiment started taking data at the SuperKEKB collider in spring 2019. As part ofthe inner tracker system, the silicon vertex detector (SVD) has been operating reliably. It providedgood data quality, a good signal-to-noise ratio, an excellent hit efficiency greater than 99% andprecise spatial resolution, which result in good tracking efficiency. The current occupancy, whichis dominated by beam-background hits, is around 0.5% in the innermost layer and does so far notcause problems to the SVD data reconstruction. Due to the estimated increase in occupancy athigher luminosity in the next years, specific strategies aiming to preserve the tracking performancewere developed and tested on data. Strip noise, sensor currents and depletion voltages havebeen measured to check for the first effects of radiation damage. So far no harmful impact onthe detector performance has been observed. Extrapolations for the next years do not implyupcoming problems, although these background estimates are still affected by large uncertainties.No damage due to beam losses or sudden intense radiation bursts were detected

A Study of Hit-time Reconstruction of Belle II Silicon Vertex Detector

International audienceFor stable operation of the Belle II Silicon Vertex Detector in the future high-luminosity operation of SuperKEKB, we plan to reduce readout data-samples per trigger and to apply hit-selection using hit-time. To realize this plan, we developed novel hit-time estimation methods, one of which achieves the resolution of 2.28 ± 0.04 ns evaluated in the current data acquisition mode. A study using Monte Carlo simulation also confirms that the hit-selection based on this hit-time improves track reconstruction performance

Simulation of the Belle II silicon vertex detector

International audienceBelle II is the next generation B Factory experiment operating at the SuperKEKB accelerator complex at KEK in Tsukuba, Japan. It is expected to collect 50 ab−1 of data, with a target instantaneous luminosity of 6.5 × 1035 cm−2s−1, which is about 30 times larger than its predecessor, Belle. In view of the ever increasing Belle II data sample, accurate simulation of the detector is growing in importance. This poses a challenging task of compromising between the realistic modeling of the response of individual detector components and reasonable performance in terms of CPU time of the simulation. In this paper we describe the simulation of the silicon vertex detector, its performance against collision data and optimization

New Results from the Silicon Vertex Detector of the Belle II Experiment

International audienceThe Silicon Vertex Detector (SVD) consists of four layers of double-sided silicon strip sensors.The SVD is one of the two vertex subdetectors within Belle II. Since the start of data taking in 2019at the Super-KEKB collider (KEK, Japan), which has the highest peak-luminosity ever recorded,the SVD is operated reliably and with high efficiency, despite exposure to harsh beam background.Measurements using data show that the SVD has both high signal-to-noise ratio and hit efficiency,as well precise spatial resolution. Further these properties are stable over time. Recently thesimulation has been tuned, using data, to improve the agrement between data and MC for clusterproperties. The good hit-time resolution can be exploited to further improve the robustness againstthe higher levels of background expected as the instantaneous luminosity increases in the nextyears of running. First effects of radiation damage on strip noise, sensor currents and depletionvoltage have been measured, although they do not have any detrimental effect on the performanceof the detector