The Belle II experiment 1 is approaching its first physics run in 2018. Its full capability to operate at the precision frontier will need not only excellent performance of the SuperKEKB accelerator ...and the detector, but also advanced calibration methods combined with data quality monitoring. To deliver data in a form suitable for analysis as soon as possible, an automated Calibration Framework (CAF) has been developed. The CAF integrates various calibration algorithms and their input collection methods for event-level data. It allows execution of the calibration workflow using different backends from local machines to a computing cluster, resolution of dependencies among algorithms, management of the produced calibration constants, and database access across possible iterations. One of the main algorithms fully integrated in the framework uses Millepede II 2 to solve a large minimization problem emerging in the track-based alignment and calibration of the pixel and strip detector, the central drift chamber, and the muon system. Advanced fitting tools are used to properly describe the detector material and magnetic field and include measurements of different sub-detectors into a single global fit performed by Millepede. This talk will present the design of the calibration framework, the integration of the Millepede calibration, and its current performance.
We present the first measurements of absolute branching fractions of Ξ_{c}^{0} decays into Ξ^{-}π^{+}, ΛK^{-}π^{+}, and pK^{-}K^{-}π^{+} final states. The measurements are made using a dataset ...comprising (772±11)×10^{6} BBover ¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB e^{+}e^{-} collider. We first measure the absolute branching fraction for B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0} using a missing-mass technique; the result is B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})=(9.51±2.10±0.88)×10^{-4}. We subsequently measure the product branching fractions B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→Ξ^{-}π^{+}), B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→ΛK^{-}π^{+}), and B(B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0})B(Ξ_{c}^{0}→pK^{-}K^{-}π^{+}) with improved precision. Dividing these product branching fractions by the result for B^{-}→Λover ¯_{c}^{-}Ξ_{c}^{0} yields the following branching fractions: B(Ξ_{c}^{0}→Ξ^{-}π^{+})=(1.80±0.50±0.14)%, B(Ξ_{c}^{0}→ΛK^{-}π^{+})=(1.17±0.37±0.09)%, and B(Ξ_{c}^{0}→pK^{-}K^{-}π^{+})=(0.58±0.23±0.05)%. For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for B(Ξ_{c}^{0}→Ξ^{-}π^{+}) can be combined with Ξ_{c}^{0} branching fractions measured relative to Ξ_{c}^{0}→Ξ^{-}π^{+} to yield other absolute Ξ_{c}^{0} branching fractions.
The silicon vertex detector of the Belle II experiment Gabrielli, A.; Adamczyk, K.; Aihara, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2024, Volume:
1064
Journal Article
Peer reviewed
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.
The Silicon Vertex Detector of the Belle II experiment Wang, Z.; Adamczyk, K.; Aggarwal, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2024, Volume:
1061
Journal Article
Peer reviewed
Open access
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.
We report the first observation of the double strange baryon Ξ(1620)^{0} in its decay to Ξ^{-}π^{+} via Ξ_{c}^{+}→Ξ^{-}π^{+}π^{+} decays based on a 980 fb^{-1} data sample collected with the Belle ...detector at the KEKB asymmetric-energy e^{+}e^{-} collider. The mass and width are measured to be 1610.4±6.0(stat)_{-4.2}^{+6.1} (syst) MeV/c^{2} and 59.9±4.8(stat)_{-7.1}^{+2.8}(syst) MeV, respectively. We obtain 4.0σ evidence of the Ξ(1690)^{0} with the same data sample. These results shed light on the structure of hyperon resonances with strangeness S=-2.
The silicon vertex detector of the Belle II experiment Irmler, C.; Adamczyk, K.; Aggarwal, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2023, Volume:
1045
Journal Article
Peer reviewed
Open access
The Belle II experiment is taking data at the asymmetric SuperKEKB collider (KEK, Japan), which operates at the Υ(4S) 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.
We present the first model-independent measurement of the CKM unitarity triangle angle ϕ3 using B±→ D(KS0\ {K}_{\mathrm{S}}^0 \π+π−π0) K± decays, where D indicates either a D0 or D¯\ \overline{D} \0 ...meson. Measurements of the strong-phase difference of the D →KS0\ {K}_{\mathrm{S}}^0 \π+π−π0 amplitude obtained from CLEO-c data are used as input. This analysis is based on the full Belle data set of 772 × 106BB¯\ \overline{B} \ events collected at the Υ(4S) resonance. We obtain ϕ3 = (5.7−8.8+10.2\ {5.7}_{-8.8}^{+10.2} \±3.5±5.7)° and the suppressed amplitude ratio rB = 0.323±0.147±0.023±0.051. Here the first uncertainty is statistical, the second is the experimental systematic, and the third is due to the precision of the strong-phase parameters measured from CLEO-c data. The 95% confidence interval on ϕ3 is (−29.7, 109.5)°, which is consistent with the current world average.
Beam background study for the Belle II Silicon Vertex Detector Tanigawa, H.; Adamczyk, K.; Aihara, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2020, Volume:
982
Journal Article
Peer reviewed
The Belle II experiment aims to accumulate 50ab−1 of e+e− collision data at the SuperKEKB asymmetric energy collider (Tsukuba, Japan). The first physics data using all Belle II detectors were taken ...in spring 2019.
In the vast physics program of the Belle II experiment, the vertex detector plays a crucial role for the determination of the B-meson decay vertices. It consists of two inner layers of pixelated silicon detectors and four outer layers of double-sided silicon strip detectors (SVD).
To achieve a design luminosity of 8×1035cm−2s−1, 40 times higher than the recorded luminosity of its predecessor, the SuperKEKB collider squeezes the beams to a vertical size of 50 nm (“nano-beam scheme”) and doubles the beam currents.
Therefore, the detectors are required to tolerate intense beam induced background due to the very high luminosity. During the 2019 spring run we measured the occupancy rate in the SVD to estimate the level of the beam induced background. With the low initial luminosity, the observed beam induced background mostly originated from Touschek processes and beam-gas scattering within individual beams. Since these different background contributions depend differently on accelerator conditions, such as the beam current, beam size and pressure, they can be disentangled. We estimate the background rate of each contribution and compare them with simulated ones. The results enable us to predict the background levels at increased beam currents and luminosity in the coming years. They also hint at background mitigation measures for running at higher luminosity. In this proceeding we present the results of our study of the beam induced background in the SVD and the prospects for future operation.
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