From April to July 2018, a data sample at the peak energy of the resonance was collected with the Belle II detector at the SuperKEKB electron-positron collider. This is the first data sample of the ...Belle II experiment. Using Bhabha and digamma events, we measure the integrated luminosity of the data sample to be ( , where the first uncertainty is statistical and the second is systematic. This work provides a basis for future luminosity measurements at Belle II.
The Belle II Physics Book Urquijo, P.; Bell, G.; Bigi, I. I. ...
Progress of theoretical and experimental physics,
12/2019, Letnik:
2019, Številka:
12
Journal Article
Recenzirano
Odprti dostop
We present the physics program of the Belle II experiment, located on the intensity frontier SuperKEKB e+e- collider. Belle II collected its first collisions in 2018, and is expected to operate for ...the next decade. It is anticipated to collect 50/ab of collision data over its lifetime. This book is the outcome of a joint effort of Belle II collaborators and theorists through the Belle II theory interface platform (B2TiP), an effort that commenced in 2014. The aim of B2TiP was to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, tau, quarkonium, electroweak precision measurements and dark sector searches. It is composed of nine working groups (WGs), which are coordinated by teams of theorist and experimentalists conveners: Semileptonic and leptonic B decays, Radiative and Electroweak penguins, φ1 and φ2 (time-dependent CP violation) measurements, φ3 measurements, Charmless hadronic B decay, Charm, Quarkonium(like), tau and low-multiplicity processes, new physics and global fit analyses. This book highlights "golden- and silver-channels", i.e. those that would have the highest potential impact in the field. Theorists scrutinised the role of those measurements and estimated the respective theoretical uncertainties, achievable now as well as prospects for the future. Experimentalists investigated the expected improvements with the large dataset expected from Belle II, taking into account improved performance from the upgraded detector.
In special tests, the active layers of the CALICE Digital Hadron Calorimeter prototype, the DHCAL, were exposed to low energy particle beams, without being interleaved by absorber plates. The ...thickness of each layer corresponded approximately to 0.29 radiation lengths or 0.034 nuclear interaction lengths, defined mostly by the copper and steel skins of the detector cassettes. This paper reports on measurements performed with this device in the Fermilab test beam with positrons in the energy range of 1 to 10 GeV. The measurements are compared to simulations based on GEANT4 and a standalone program to emulate the detailed response of the active elements.
This paper describes an analysis performed at 250 GeV centre of mass energy for the reaction e+e- -> bbbar with the International Linear Collider, ILC, assuming an integrated luminosity of 500 fb-1. ...This measurement requires determining the b quark charge, which can be optimally performed using the precise micro-vertex detector of the detector ILD and the charged kaon identification provided by the dE/dx information of its TPC. Given that the forward backward asymmetry is maximal for e-L (Left-handed electron polarisation), it has been necessary to develop a new method to correct for unavoidable angular migration due to b charge mis-measurements. This correction is based on the reconstructed events themselves without introducing external corrections which would induce large uncertainties. With polarized beams, one can separate the Z and photon vector and axial couplings to b quarks. The precision reached is at the few per mill level, and should allow to confirm/discard the deviation observed at LEP1 on the ZbRbR coupling. Model independent upper bounds on the tensor couplings, F2V and F2A, are derived using the shape of the angular distribution.
We present the novel implementation of a non-differentiable metric approximation and a corresponding loss-scheduling aimed at the search for new particles of unknown mass in high energy physics ...experiments. We call the loss-scheduling, based on the minimisation of a figure-of-merit related function typical of particle physics, a Punzi-loss function, and the neural network that utilises this loss function a Punzi-net. We show that the Punzi-net outperforms standard multivariate analysis techniques and generalises well to mass hypotheses for which it was not trained. This is achieved by training a single classifier that provides a coherent and optimal classification of all signal hypotheses over the whole search space. Our result constitutes a complementary approach to fully differentiable analyses in particle physics. We implemented this work using PyTorch and provide users full access to a public repository containing all the codes and a training example.
We present the novel implementation of a non-differentiable metric approximation and a corresponding loss-scheduling aimed at the search for new particles of unknown mass in high energy physics ...experiments. We call the loss-scheduling, based on the minimisation of a figure-of-merit related function typical of particle physics, a Punzi-loss function, and the neural network that utilises this loss function a Punzi-net. We show that the Punzi-net outperforms standard multivariate analysis techniques and generalises well to mass hypotheses for which it was not trained. This is achieved by training a single classifier that provides a coherent and optimal classification of all signal hypotheses over the whole search space. Our result constitutes a complementary approach to fully differentiable analyses in particle physics. We implemented this work using PyTorch and provide users full access to a public repository containing all the codes and a training example.
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.
Phys. Rev. D 104, 012007 (2021) We report the first search for the penguin-dominated process $B_{s}^{0}
\rightarrow \eta^{\prime} X_{s\bar{s}}$ using a semi-inclusive method. A 121.4
...$\mathrm{fb}^{-1}$ integrated luminosity $\Upsilon(5S)$ data set collected by
the Belle experiment, at the KEKB asymmetric-energy $e^+e^-$ collider, is used.
We observe no statistically significant signal and including all uncertainties,
we set a 90\% confidence level upper limit on the partial branching fraction at
1.4 $\times$ 10$^{-3}$ for $M(X_{s\bar{s}})$ $\leq$ 2.4 GeV/$c^{2}$.
The technological prototype of the CALICE highly granular silicon-tungsten electromagnetic calorimeter (SiW-ECAL) was tested in a beam at DESY in 2017. The setup comprised seven layers of silicon ...sensors. Each layer comprised four sensors, with each sensor containing an array of 256 \(5.5\times5.5\) mm\(^2\) silicon PIN diodes. The four sensors covered a total area of \(18\times18\) cm\(^2\), and comprised a total of 1024 channels. The readout was split into a trigger line and a charge signal line. Key performance results for signal over noise for the two output lines are presented, together with a study of the uniformity of the detector response. Measurements of the response to electrons for the tungsten loaded version of the detector are also presented.
In this article we describe the commissioning and a first analysis of the the beam test performance of a small prototype of a highly granular silicon tungsten calorimeter. The prototype features ...detector elements with a channel number similar to that envisaged for e.g. the ILD Detector of the International Linear Collider (ILC). The analysis demonstrates the capability of the detector to record signals as low as 0.5 MIP. Further, no loss of performance has been observed when operating the detector in a high magnetic field.
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