Phys. Rev. Lett. 130, 181803 (2023) We search for lepton-flavor-violating $\tau^-\to e^-\alpha$ and
$\tau^-\to\mu^-\alpha$ decays, where $\alpha$ is an invisible spin-0 boson. The
search uses ...electron-positron collisions at $10.58$ GeV center-of-mass energy
with an integrated luminosity of $62.8$ fb$^{-1}$, produced by the SuperKEKB
collider and collected with the Belle II detector. We search for an excess in
the lepton-energy spectrum of the known $\tau^-\to e^-\bar\nu_e \nu_\tau$ and
$\tau^-\to \mu^-\bar\nu_\mu \nu_\tau$ decays. We report 95\% confidence-level
upper limits on the branching-fraction ratio ${\mathcal B}(\tau^-\to e^-
\alpha) / {\mathcal B}(\tau^- \to e^- \bar\nu_e \nu_\tau)$ in the range
$(1.1-9.7) \times 10^{-3}$ and on ${\mathcal B}(\tau^-\to \mu^- \alpha) /
{\mathcal B}(\tau^- \to \mu^- \bar\nu_\mu \nu_\tau)$ in the range $(0.7-12.2)
\times 10^{-3}$ for $\alpha$ masses between 0 and 1.6 GeV/c$^2$. These results
provide the most stringent bounds on invisible boson production from $\tau$
decays.
Phys. Rev. Lett. 130, 231801 (2023) The $L_{\mu}-L_{\tau}$ extension of the standard model predicts the existence
of a lepton-flavor-universality-violating $Z^{\prime}$ boson that couples only
to the ...heavier lepton families. We search for such a $Z^\prime$ through its
invisible decay in the process $e^+ e^- \to \mu^+ \mu^- Z^{\prime}$. We use a
sample of electron-positron collisions at a center-of-mass energy of 10.58GeV
collected by the Belle II experiment in 2019-2020, corresponding to an
integrated luminosity of 79.7fb$^{-1}$. We find no excess over the expected
standard-model background. We set 90$\%$-confidence-level upper limits on the
cross section for this process as well as on the coupling of the model, which
ranges from $3 \times 10^{-3}$ at low $Z^{\prime}$ masses to 1 at $Z^{\prime}$
masses of 8$GeV/c^{2}$.
A complex approach to the choice of color masterbatches for rigid PVC compounds dyeing directly during high-speed extrusion is proposed in this paper. The data is shown to improve the thermal ...stability of rigid PVC compounds with new organosilicon modifiers. To evaluate the characteristics of pigment masterbatches it is suggested to use differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), which allow determining the thermal stability, structure and behavior of the pigment masterbatch upon heating. These results will allow creating a fundamental basis for the synthesis and development of new pigments and masterbatches, formulate the requirements for the characteristics and choice of masterbatches taking into account the formulation of the polymer composition.
The 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 paper presents the results of the analysis of rigid PVС compositions with different fillers. As the fillers were used powders of chalk, diatomite, zeolite, and shungite, which differed in ...dispersity and chemical nature. The melt viscosity of the filled PVC blends and moments on Brabender rotors were analyzed by using Mooney's equation. A conclusion about the thickness of the polymer layers with the lowered mobility on the filler surface was made. The results can be useful for developers of PVC compositions for different purposes.
In 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.
Eur. Phys. J. C 82, 283 (2022) We report on new flavor tagging algorithms developed to determine the
quark-flavor content of bottom ($B$) mesons at Belle II. The algorithms provide
essential inputs ...for measurements of quark-flavor mixing and charge-parity
violation. We validate and evaluate the performance of the algorithms using
hadronic $B$ decays with flavor-specific final states reconstructed in a data
set corresponding to an integrated luminosity of $62.8$ fb$^{-1}$, collected at
the $\Upsilon$(4$S$) resonance with the Belle II detector at the SuperKEKB
collider. We measure the total effective tagging efficiency to be
$\varepsilon_{\rm eff} = \big(30.0 \pm 1.2(\text{stat}) \pm
0.4(\text{syst})\big)\%$ for a category-based algorithm and $\varepsilon_{\rm
eff} = \big(28.8 \pm 1.2(\text{stat}) \pm 0.4(\text{syst})\big)\%$ for a
deep-learning-based algorithm.
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