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

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 Belle II Silicon Vertex Detector: Performance and Operational Experience in the First Year of Data Taking

International audienceIn spring 2019 the Belle II experiment at the high-luminosity SuperKEKB e^+e^− collider (KEK, Japan) has resumed operation after the installation of the new vertex detector. In the first period of operation SuperKEKB has already reached the record luminosity of 2.4 × 10^34 cm^−2 s^−1 which will be increased by about a factor 30 in the coming years. Two inner layers of DEPFET-based pixels and four layers of double-sided silicon strip detectors (Silicon Vertex Detector, SVD) make up this new vertex detector, designed to meet the stringent physics requirements as well as to cope with the high beam background conditions. Since the beginning of data taking, the SVD has been functioning with a very reliable and stable operation and excellent detector performance. The first evidence of radiation effects in the SVD have been observed, which are at the expected level and not affecting performance. This paper will review the performance achieved by the SVD and the lessons learned in the first year of operation that continued even during the COVID-19 pandemic

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

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

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

For 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

Particle Identification in Belle II Silicon Vertex Detector

International audienceWe report a particle identification (PID) tool developed using energy-loss information in the silicon-strip vertex detector (SVD) of Belle II for charged pions, kaons, and protons using $D^{* + } \to D^{0}[ \to K^{ - }\pi ^{ + }]\pi ^{ + }$ and $\Lambda \to p\pi ^{ - }$ decay samples. The study is based on e^+e^− collision data recorded at the $\Upsilon (4S)$ resonance by Belle II and the results are compared with that of a Monte Carlo sample. The introduction of additional information from the SVD is found to improve the overall PID performance in the low-momentum region