We present an up-to-date profile of the Cabibbo-Kobayashi-Maskawa matrix with emphasis on the interpretation of recent CP-violation results from the B factories. For this purpose, we review all ...relevant experimental and theoretical inputs from the contributing domains of electroweak interaction. We give the “standard” determination of the apex of the Unitarity Triangle, namely the Wolfenstein parameters \(\overline\rho\) and \(\overline\eta\), by means of a global CKM fit. The fit is dominated by the precision measurement of \(\sin 2 \beta\) by the B factories. A detailed numerical and graphical study of the impact of the results is presented. We propose to include \(\sin 2\alpha\) from the recent measurement of the time-dependent CP-violating asymmetries in \(B^0\to\rho^ + \rho^-\), using isospin relations to discriminate the penguin contribution. The constraint from \(\varepsilon^\prime/\varepsilon\) is discussed. We study the impact from the branching fraction measurement of the rare kaon decay \(K^ + \to\pi^ + \nu\overline\nu\), and give an outlook into the reach of a future measurement of \(K^0_L\to\pi^0\nu\overline\nu\). The B system is investigated in detail. We display the constraint on \(2\beta + \gamma\) and \(\gamma\) from \(B^0\to D^{(*)\pm}\pi^\mp\) and \(B^ + \to D^{(*)0}K^ + \) decays, respectively. A significant part of this paper is dedicated to the understanding of the dynamics of B decays into \(\pi\pi\), \(K\pi\), \(\rho\pi\), \(\rho\rho\) and modes related to these by flavor symmetry. Various phenomenological approaches and theoretical frameworks are discussed. We find a remarkable agreement of the \(\pi\pi\) and \(K\pi\) data with the other constraints in the unitarity plane when the hadronic matrix elements are calculated within QCD Factorization, where we apply a conservative treatment of the theoretical uncertainties. A global fit of QCD Factorization to all \(\pi\pi\) and \(K\pi\) data leads to precise predictions of the related observables. However sizable phenomenological power corrections are preferred. Using an isospin-based phenomenological parameterization, we analyze separately the \(B\to K\pi\) decays, and the impact of electroweak penguins in response to recent discussions. We find that the present data are not sufficiently precise to constrain either electroweak parameters or hadronic amplitude ratios. We do not observe any unambiguous sign of New Physics, whereas there is some evidence for potentially large non-perturbative rescattering effects. Finally we use a model-independent description of a large class of New Physics effects in both \(B^0\overline B^0\) mixing and B decays, namely in the \(b\to d\) and \(b\to s\) gluonic penguin amplitudes, to perform a new numerical analysis. Significant non-standard corrections cannot be excluded yet, however Standard Model solutions are favored in most cases. In the appendix to this paper we propose a frequentist method to extract a confidence level on \(\Delta m_s\) from the experimental information on \(B^0_s \overline B_s^0\) oscillation. In addition we describe a novel approach to combine potentially inconsistent measurements. All results reported in this paper have been obtained with the numerical analysis package CKMfitter, featuring the frequentist statistical approach Rfit.
We report on a new approach to a global CKM matrix analysis taking into account most recent experimental and theoretical results. The statistical framework (Rfit) developed in this paper advocates ...frequentist statistics. Other approaches, such as Bayesian statistics or the 95% CL scan method are also discussed. We emphasize the distinction of a model testing and a model dependent, metrological phase in which the various parameters of the theory are estimated. Measurements and theoretical parameters entering the global fit are thoroughly discussed, in particular with respect to their theoretical uncertainties. Graphical results for confidence levels are drawn in various one and two-dimensional parameter spaces. Numerical results are provided for all relevant CKM parameterizations, the CKM elements and theoretical input parameters. Predictions for branching ratios of rare K and B meson decays are obtained. A simple, predictive SUSY extension of the Standard Model is discussed.
Abstract
The Aerogel Ring Imaging Cherenkov (ARICH) counter serves as a particle identification device in the forward end-cap region of the Belle II spectrometer. It is capable of identifying pions ...and kaons with momenta up to $4\>$GeV$\>$c$^{-1}$ by detecting Cherenkov photons emitted in the silica aerogel radiator. After the detector alignment and calibration of the probability density function, we evaluate the performance of the ARICH counter using early beam collision data. Event samples of $D^{\ast +} \to D^0 \pi^+ (D^0 \to K^-\pi^+)$ were used to determine the $\pi(K)$ efficiency and the $K(\pi)$ misidentification probability. We found that the ARICH counter is capable of separating kaons from pions with an identification efficiency of $93.5 \pm 0.6 \, \%$ at a pion misidentification probability of $10.9 \pm 0.9 \, \%$. This paper describes the identification method of the counter and the evaluation of the performance during its early operation.
Calibration of the Belle II aerogel ring imaging detector Pestotnik, R.; Adachi, I.; Burmistrov, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2020, Volume:
952
Journal Article
Peer reviewed
For efficient separation of hadrons in the forward end-cap of the Belle II spectrometer, an aerogel proximity focusing Ring Imaging Detector is installed in the high magnetic field between the ...central drift chamber and electromagnetic calorimeter. Cherenkov photons, emitted in the double layer aerogel radiator are expanded through the empty space and detected on the photon detector consisting of Hybrid Avalanche Photo diodes. The readout electronics working in a threshold mode records hit patterns registered during beam collisions. A particle identification algorithm based on the two dimensional extended maximum likelihood technique is used to assign probabilities for different particle hypotheses of tracks traversing the aerogel RICH detector. For efficient discrimination, the Aerogel RICH detector has to be calibrated. We present the key calibration steps used to optimize the detector performance.
First experience with Belle II Aerogel RICH detector Mrvar, M.; Adachi, I.; Burmistrov, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
08/2019, Volume:
936
Journal Article
Peer reviewed
The Aerogel Ring-Imaging Cherenkov (ARICH) detector provides particle identification information in the forward endcap part of Belle II. It efficiently separates charged kaons from pions for momenta ...between 0.5GeV/c and 4.0GeV/c. Optical photons are emitted in a double layer aerogel radiator and detected by Hybrid Avalanche Photo Detectors. ARICH was installed in Belle II at the end of 2017, the first phase of a complex detector calibration of electronic signals and preparation for physics signals calibration has been successfully concluded. Cherenkov rings, created by cosmic rays as well as by charged particles from beam collisions, have been observed. The kaon identification efficiency using D±∗ decays has been studied and its calibration is expected by the end of the commissioning phase when sufficient data is available.
•The commissioning phase of Belle II is completed.•Cherenkov rings, created by cosmic rays and at collisions, were observed in ARICH.•The ARICH performance is studied using charged kaons and pions from D̂{+*} decays
The Belle II experiment is a new generation B factory experiment at the SuperKEKB electron–positron collider. The main purpose of the experiment is to search for new physics with a large sample of B ...meson decays. The proximity-focusing Aerogel Ring-Imaging Cherenkov detector (ARICH) has been designed to identify kaons and pions in the forward end-cap of the Belle II spectrometer. Using aerogel as radiator with specialized photon sensors called HAPD, the K/π separation is expected to reach more than 4 σ in the momentum range from 0.5 GeV/c to 4.0 GeV/c. ARICH detector was constructed in summer 2017 and was installed in the Belle II spectrometer in the beam line of the SuperKEKB collider. The test of the ARICH detector is performed using both cosmic rays and the beam collisions during the accelerator commissioning. We observe Cherenkov rings in the ARICH detector associated with charged tracks detected by the tracking system. The reconstructed Cherenkov angle distribution has a clear and reasonable peak. The ARICH K∕π separation performance is evaluated using Bhabha events in beam runs; the separation power achieve the design value.
Front-end electronics of the Belle II aerogel ring imaging detector Pestotnik, R.; Adachi, I.; Burmistrov, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2020, Volume:
952
Journal Article
Peer reviewed
A proximity focusing RICH detector with an aerogel radiator is used for charged particle identification in the forward end-cap of the Belle II spectrometer. The detector, consisting of a 4 cm aerogel ...radiator, a 16 cm expansion volume and a photon detector with 420 Hybrid Avalanche Photo Detectors, is mounted in a very confined space between Central Drift Chamber and Electromagnetic Calorimeter, allowing only 5 cm of space for the readout electronics. In our solution, low power front-end read-out boards are mounted at the back side of each of the HAPD photosensors. These boards have each been tested individually before their installation onto the photosensors and into the spectrometer. Most important design issues and first experiences with the aforementioned front-end read-out boards are presented in this contribution.
We report a measurement of the D0 and D+ lifetimes using D0 → K-π+ and D+ → K-π+π+ decays reconstructed in e+e- → $c\bar{c}$ data recorded by the Belle II experiment at the SuperKEKB ...asymmetric-energy e+e- collider. The data, collected at center-of-mass energies at or near the Υ(4S) resonance, correspond to an integrated luminosity of 72 fb-1. The results, τ(D0) = 410.5 1.1 (stat) 0.8 (syst) fs and τ(D+) = 1030.4 4.7 (stat) 3.1 (syst) fs, are the most precise to dateand are consistent with previous determinations.
We search for single-photon events in 53 fb^{-1} of e^{+}e^{-} collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a ...large missing momentum and energy, consistent with production of a spin-1 particle A^{'} through the process e^{+}e^{-}→γA^{'}; A^{'}→invisible. Such particles, referred to as "dark photons," are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A^{'} to e^{+}e^{-} in the mass range m_{A^{'}}≤8 GeV. In particular, our limits exclude the values of the A^{'} coupling suggested by the dark-photon interpretation of the muon (g-2)_{μ} anomaly, as well as a broad range of parameters for the dark-sector models.
A search for the flavor-changing neutral-current decay B+ →K+$ν\bar{ν}$ is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample ...corresponds to an integrated luminosity of 63 fb-1 collected at the Υ (4S) resonance and a sample of 9 fb-1 collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B+ →K+$ν\bar{ν}$ decay, but also the inclusive properties of the other B meson in the Υ(4S) $B\bar{B}$ event, to suppress the background from other B meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of B+ →K+$ν\bar{ν}$ of 4.1 × 10-5 is set at the 90% confidence level.
PDF
