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.
SuperKEKB, the next generation B factory, has been constructed in Japan as an upgrade of KEKB. This brand new e+ e- collider is expected to deliver a very large data set for the Belle II experiment, ...which will be 50 times larger than the previous Belle sample. Both the triggered physics event rate and the background event rate will be increased by at least 10 times than the previous ones, and will create a challenging data taking environment for the Belle II detector. The software system of the Belle II experiment is designed to execute this ambitious plan. A full detector simulation library, which is a part of the Belle II software system, is created based on Geant4 and has been tested thoroughly. Recently the library has been upgraded with Geant4 version 10.1. The library is behaving as expected and it is utilized actively in producing Monte Carlo data sets for various studies. In this paper, we will explain the structure of the simulation library and the various interfaces to other packages including geometry and beam background simulation.
This article presents a reciprocal model of mentoring as an alternative approach to more traditional mentoring models. A mentor, experienced with online course delivery and pedagogy, worked with six ...online instructors over two academic terms within a reciprocal mentorship model. This model was designed to build a collaborative learning relationship which would benefit each partner. The mentoring was scheduled on a just-in-time basis in response to each online instructor's needs. Study results show that the time commitments required to accomplish the goals of the mentoring project were challenging for participants; that post-secondary institutions have a responsibility to provide multiple supports (including, for example, mentoring assistance) for faculty members teaching online; and that developing a structured mentoring program could facilitate a more effective reciprocal mentoring process, with benefits for both mentors and mentees.
We present the results of a search for the b → d ℓ + ℓ − flavor-changing neutral-current rare decays B + , 0 → ( η , ω , π + , 0 , ρ + , 0 ) e + e − and B + , 0 → ( η , ω , π 0 , ρ + ) μ + μ − using ...a 711 fb − 1 data sample that contains 772 × 10 6 B B ¯ events. The data were collected at the ϒ ( 4 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. We find no evidence for signal and set upper limits on branching fractions at the 90% confidence level in the range ( 3.8 – 47 ) × 10 − 8 depending on the decay channel. The obtained limits are the world’s best results. This is the first search for the channels B + , 0 → ( ω , ρ + , 0 ) e + e − and B + , 0 → ( ω , ρ + ) μ + μ − . Published by the American Physical Society 2024
We report the result of a search for the rare decay
B
0
→
γ
γ
using a combined dataset of
753
×
10
6
B
B
¯
pairs collected by the Belle experiment and
387
×
10
6
B
B
¯
pairs collected by the ...Belle II experiment from decays of the
ϒ
(
4
S
)
resonance produced in
e
+
e
−
collisions. A simultaneous fit to the Belle and Belle II data sets yields
11.0
−
5.5
+
6.5
signal events, corresponding to a
2.5
σ
significance. We determine the branching fraction
B
(
B
0
→
γ
γ
)
=
(
3.7
−
1.8
+
2.2
(
stat
)
±
0.5
(
syst
)
)
×
10
−
8
and set a 90% credibility level upper limit of
B
(
B
0
→
γ
γ
)
<
6.4
×
10
−
8
.
<supplementary-material>
<copyright-statement>Published by the American Physical Society</copyright-statement>
2024
</supplementary-material>
We measure the branching fraction of the decay B − → D 0 ρ ( 770 ) − using data collected with the Belle II detector. The data contain 387 million B B ¯ pairs produced in e + e − collisions at the ϒ ...( 4 S ) resonance. We reconstruct 8360 ± 180 decays from an analysis of the distributions of the B − energy and the ρ ( 770 ) − helicity angle. We determine the branching fraction to be ( 0.939 ± 0.021 ( stat ) ± 0.050 ( syst ) ) % , in agreement with previous results. Our measurement improves the relative precision of the world average by more than a factor of two. Published by the American Physical Society 2024
Abstract We present measurements of the branching fractions of eight $$ {\overline{B}}^0 $$ B ¯ 0 → D (*)+ K − $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 , B − → D (*)0 K − $$ ...{K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Υ(4 S ) resonance collected with the Belle II detector, corresponding to an integrated luminosity of 362 fb − 1 . The event yields are extracted from fits to the distributions of the difference between expected and observed B meson energy, and are efficiency-corrected as a function of m ( K − $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 ) and m ( D (*) $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 ) in order to avoid dependence on the decay model. These results include the first observation of $$ {\overline{B}}^0 $$ B ¯ 0 → D + K − $$ {K}_S^0 $$ K S 0 , B − → D* 0 K − $$ {K}_S^0 $$ K S 0 , and $$ {\overline{B}}^0 $$ B ¯ 0 → D* + K − $$ {K}_S^0 $$ K S 0 decays and a significant improvement in the precision of the other channels compared to previous measurements. The helicity-angle distributions and the invariant mass distributions of the K − $$ {K}_{(S)}^{\left(\ast \right)0} $$ K S ∗ 0 systems are compatible with quasi-two-body decays via a resonant transition with spin-parity J P = 1 − for the K − $$ {K}_S^0 $$ K S 0 systems and J P = 1 + for the K − K* 0 systems. We also present measurements of the branching fractions of four $$ {\overline{B}}^0 $$ B ¯ 0 → D (*)+ $$ {D}_s^{-} $$ D s − , B − → D (*)0 $$ {D}_s^{-} $$ D s − decay channels with a precision compatible to the current world averages.
The Silicon Vertex Detector of the Belle II experiment Uematsu, Y.; Adamczyk, K.; Aggarwal, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2022, Letnik:
1033
Journal Article
Recenzirano
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.
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