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.
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.
The Silicon Vertex Detector of the Belle II experiment Zani, L.; Adamczyk, K.; Aggarwal, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2022, Volume:
1038
Journal Article
Peer reviewed
Open access
Since 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.
A
bstract
We report the first measurement of the inclusive
e
+
e
−
→
$$ b\overline{b} $$
b
b
¯
→
$$ {D}_s^{\pm } $$
D
s
±
X
and
e
+
e
−
→
$$ b\overline{b} $$
b
b
¯
→ D
0
/
$$ {\overline{D}}^0 $$
D
¯
...0
X
cross sections in the energy range from 10
.
63 to 11
.
02 GeV. Based on these results, we determine
σ
(
e
+
e
−
→
$$ {B}_s^0{\overline{B}}_s^0 $$
B
s
0
B
¯
s
0
X
) and
σ
(
e
+
e
−
→
$$ B\overline{B} $$
B
B
¯
X
) in the same energy range. We measure the fraction of
$$ {B}_s^0 $$
B
s
0
events at Υ(10860) to be
f
s
= (
$$ {22.0}_{-2.1}^{+2.0} $$
22.0
−
2.1
+
2.0
)%. We determine also the ratio of the
$$ {B}_s^0 $$
B
s
0
inclusive branching fractions
$$ \mathcal{B} $$
B
(
$$ {B}_s^0 $$
B
s
0
→ D
0
/
$$ {\overline{D}}^0 $$
D
¯
0
X
)
/
$$ \mathcal{B} $$
B
(
$$ {B}_s^0 $$
B
s
0
→
$$ {D}_s^{\pm } $$
D
s
±
X
) = 0
.
416 ± 0
.
018 ± 0
.
092. The results are obtained using the data collected with the Belle detector at the KEKB asymmetric-energy
e
+
e
−
collider.
Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays τ± → ℓ±γ (ℓ = e, μ) are predicted to ...have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via τ± → ℓ±γ using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb–1, is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions, B(τ± → μ±γ) ≤ 4.2 × 10–8 and B(τ± → e±γ) ≤ 5.6 × 10–8, are set at 90% confidence level.
We report a study of Λc+→Λh+ and Λc+→Σ0h+ (h=K,π) decays based on a data sample of 980fb-1 collected with the Belle detector at the KEKB energy-asymmetric e+e- collider. The first results of direct ...CP asymmetry in two-body singly Cabibbo-suppressed (SCS) decays of charmed baryons are measured, ACPdir(Λc+→ΛK+)=+0.021±0.026±0.001 and ACPdir(Λc+→Σ0K+)=+0.025±0.054±0.004. We also make the most precise measurement of the decay asymmetry parameters (α) for the four modes of interest and search for CP violation via the α-induced CP asymmetry (ACPα). We measure ACPα(Λc+→ΛK+)=-0.023±0.086±0.071 and ACPα(Λc+→Σ0K+)=+0.08±0.35±0.14, which are the first ACPα results for SCS decays of charmed baryons. We search for Λ-hyperon CP violation in Λc+→(Λ,Σ0)π+ and find ACPα(Λ→pπ-)=+0.013±0.007±0.011. This is the first time that hyperon CP violation has been measured via Cabibbo-favored charm decays. No evidence of baryon CP violation is found. We also obtain the most precise branching fractions for two SCS Λc+ decays, B(Λc+→ΛK+)=(6.57±0.17±0.11±0.35)×10-4 and B(Λc+→Σ0K+)=(3.58±0.19±0.06±0.19)×10-4. The first uncertainties are statistical and the second systematic, while the third uncertainties come from the uncertainties on the world average branching fractions of Λc+→(Λ,Σ0)π+.
