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Register a new userFirst flavor tagging calibration using 2019 Belle II data
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We report on the first calibration of the standard Belle II $B$-flavor tagger using the full data set collected at the $Upsilon(4{rm S})$ resonance in 2019 with the Belle II detector at the SuperKEKB collider, corresponding to 8.7 fb$^{-1}$ of integrated luminosity. The calibration is performed by reconstructing various hadronic charmed $B$-meson decays with flavor-specific final states. We use simulation to optimize our event selection criteria and to train the flavor tagging algorithm. We determine the tagging efficiency and the fraction of wrongly identified tag-side $B$~candidates from a measurement of the time-integrated $B^0-overline{B}^0$ mixing probability. The total effective efficiency is measured to be $varepsilon_{rm eff} = big(33.8 pm 3.6(text{stat}) pm 1.6(text{sys})big)%$, which is in good agreement with the predictions from simulation and comparable with the best one obtained by the Belle experiment. The results show a good understanding of the detector performance and offer a basis for future calibrations.
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We report on the reconstruction of various charmless $B$ decays from electron-positron collisions at the energy corresponding to the $Upsilon(4S)$ resonance collected with the Belle II detector at the SuperKEKB collider. We use simulation to devise optimized event selections and apply them to the full data set collected in 2019, corresponding to 8.7,fb$^{-1}$ of integrated luminosity. We fit the difference between half of the collision energy and the $B$ candidate energy (in the $Upsilon(4S)$ frame) for events restricted to a signal-rich range in beam-energy-constrained mass to search for charmless signals. Signal yields of approximately 80, 15, 20, 30, 90, and 160 decays are reconstructed for the channels $B^0 to K^+pi^-$, $B^0 to pi^+pi^-$, $B^+ to K^0_S(to pi^+pi^-)pi^+$, $B^+ to K^+pi^0(to gammagamma)$, $B^+ to K^+K^-K^+$, and $B^+ to K^+pi^-pi^+$, respectively. Yields and background contaminations are compatible with those expected from simulation and comparable with those obtained by the Belle experiment. The results show a good understanding of the detector performance and offer a reliable basis to assess projections for future reach.
This note describes the rediscovery of $Btoeta K$ decays in Belle II data, both in the charged and neutral final state: $B_0toeta K_S$ and $B^pmtoeta K^pm$. The $eta$ is searched for in two decay modes: $etatoetapi^+pi^-$ with $etatogammagamma$, and $etatorhogamma$. The analysis uses data collected in 2019 and 2020 at the SuperKEKB asymmetric $e^+e^-$ collider, with an integrated luminosity of $62.8~fb^{-1}$, corresponding to $68.2$ million of $Bbar{B}$ pairs produced. The signal yield is obtained via an unbinned maximum likelihood fit to signal sensitive variables, obtaining branching ratios: $$mathcal{B}left(B^pmtoetaK^pmright) = left(63.4~^{+3.4}_{-3.3},(stat),pm3.2,(syst),right) times10^{-6} $$ $$mathcal{B}left(B_0toetaK_Sright) = left(59.9~^{+5.8}_{-5.5},(stat),pm2.9,(syst),right) times10^{-6} $$ which are consistent with world average.
This report summarizes the flavor tagging techniques developed at the CDF and D{O}experiments. Flavor tagging involves identification of the B meson flavor atproduction, whether its constituent is a quark or an anti-quark. It is crucial for measuring the oscillation frequency of neutral B mesons, both in the B^0 and B_S system. The two experiments have developed their unique approaches to flavor tagging, using neural networks, and likelihood methods to disentangle tracks from $b$ decays from other tracks. This report discusses these techniques and the measurement of B^0 mixing, as a means to calibrate the taggers.
We describe the conversion of simulated and recorded data by the Belle experiment to the Belle~II format with the software package texttt{b2bii}. It is part of the Belle~II Analysis Software Framework. This allows the validation of the analysis software and the improvement of analyses based on the recorded Belle dataset using newly developed analysis tools.
The new Belle II experiment at the asymmetric $e^+ e^-$ accelerator SuperKEKB at KEK in Japan is designed to deliver a peak luminosity of $8times10^{35}text{cm}^{-2}text{s}^{-1}$. To perform high-precision track reconstruction, e.g. for measurements of time-dependent CP-violating decays and secondary vertices, the Belle II detector is equipped with a highly segmented pixel detector (PXD). The high instantaneous luminosity and short bunch crossing times result in a large stream of data in the PXD, which needs to be significantly reduced for offline storage. The data reduction is performed using an FPGA-based Data Acquisition Tracking and Concentrator Online Node (DATCON), which uses information from the Belle II silicon strip vertex detector (SVD) surrounding the PXD to carry out online track reconstruction, extrapolation to the PXD, and Region of Interest (ROI) determination on the PXD. The data stream is reduced by a factor of ten with an ROI finding efficiency of >90% for PXD hits inside the ROI down to 50 MeV in $p_text{T}$ of the stable particles. We will present the current status of the implementation of the track reconstruction using Hough transformations, and the results obtained for simulated Upsilon(4S) $rightarrow , Bbar{B}$ events.
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