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Register a new userMeasurement of the integrated luminosity of the Phase 2 data of the Belle II experiment
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From April to July 2018, a data sample at the peak energy of the $Upsilon(4S)$ 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 ($496.3 pm 0.3 pm 3.0$)~pb$^{-1}$, where the first uncertainty is statistical and the second is systematic. This work provides a basis for future luminosity measurements at Belle~II.
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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.
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.
We present the first measurement of the time-integrated mixing probability $chi_d$ using Belle II data collected at a center-of-mass (CM) energy of 10.58 GeV, corresponding to the mass of the $Upsilon$(4S) resonance, with an integrated luminosity of $34.6 {rm fb}^{-1}$ at the SuperKEKB $e^+ e^-$ collider. We reconstruct pairs of B mesons both of which decay to semileptonic final states. Using a novel methodology, we measure $chi_d = 0.187 pm 0.010 text{ (stat.)} pm 0.019 text{ (syst.)}$, which is compatible with existing indirect and direct determinations.
To study the nature of the state $Y(2175)$, a dedicated data set of $e^+e^-$ collision data was collected at the center-of-mass energy of 2.125 GeV with the BESIII detector at the BEPCII collider. By analyzing large-angle Bhabha scattering events, the integrated luminosity of this data set is determined to be $108.49pm0.02pm0.85$ pb$^{-1}$, where the first uncertainty is statistical and the second one is systematic. In addition, the center-of-mass energy of the data set is determined with radiative dimuon events to be $2126.55pm0.03pm0.85$ MeV, where the first uncertainty is statistical and the second one is systematic.
We report a measurement of the $D^0$ and $D^+$ lifetimes using $D^0to K^-pi^+$ and $D^+to K^-pi^+pi^+$ decays reconstructed in $e^+e^-to cbar{c}$ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^+e^-$ collider. The data correspond to an integrated luminosity of $72,{rm fb}^{-1}$. The results, $tau(D^0) = 410.5pm1.1,{rm(stat)}pm0.8,{rm(syst.)},{rm fs}$ and $tau(D^+) = 1030.4pm4.7,{rm(stat)}pm3.1,{rm(syst.)},{rm fs}$, are the most precise to date and are consistent with previous determinations.
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