Search for leptonic decays of D0 mesons

We search for the flavor-changing neutral current decays D0\to mu+mu- and D0\to e+e-, and for the lepton-flavor violating decays D0\to e\pm mu\mp using 660 fb^-1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. We find no evidence for any of these decays. We obtain significantly improved upper limits on the branching fractions: B(D0\to mu+mu-)<1.4x10-7, B(D0\to e+e-)<7.9x10-8, and B(D0\to e+mu-)+B(D0\to mu+e-)<2.6x10-7 at 90% confidence level.Comment: 6 pages, 3 figure

First Observation of Radiative B^0 -> \phi K^0 \gamma Decays and Measurements of Their Time-Dependent CP Violation

We report the first observation of the radiative decay B^0 -> \phi K^0 \gamma using a data sample of 772 x 10^6 B B-bar pairs collected at the \Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider. We observe a signal of 37+/-8 events with a significance of 5.4 standard deviations including systematic uncertainties. The measured branching fraction is ${\cal B}(B^0 -> \phi K^0 \gamma) = (2.74\pm 0.60 \pm 0.32) \times 10^{-6}$, where the uncertainties are statistical and systematic, respectively. We also report the first measurements of time-dependent CP violation parameters: ${\mathcal S}_{\phi K_S^0 \gamma} = +0.74^{+0.72}_{-1.05} (stat)^{+0.10}_{-0.24} (syst)$ and ${\mathcal A}_{\phi K_S^0 \gamma} = +0.35 +/- 0.58 (stat)^{+0.23}_{-0.10} (syst)$. Furthermore, we measure ${\mathcal B}(B^+ -> \phi K^+ \gamma) = (2.48 +/- 0.30 +/- 0.24) x 10^{-6}$, ${\mathcal A}_{CP} = -0.03 +/- 0.11 +/- 0.08$ and find that the signal is concentrated in the M_{\phi K} mass region near threshold.Comment: 6 pages, 3 figures, Modified version is to be published in PRD(RC

First observation of Bs0→J/ψηB_s^0\to J/\psi\eta and Bs0→J/ψη′B_s^0\to J/\psi\eta'

We report first observations of $B_s^0\to J/\psi\eta$ and $B_s^0\to J/\psi\eta'$. The results are obtained from 121.4 fb^{-1} of data collected at the $\Upsilon(5S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. We obtain the branching fractions Br(B_s^0\to J/\psi\eta)= [5.10\pm 0.50(stat.)\pm 0.25(syst.)^{+1.14}_{-0.79}(N_{B_s^(*)\bar B_s^(*))] \times 10^{-4}, and Br(B_s^0\to J/\psi\eta')=[3.71\pm 0.61(stat.)\pm 0.18(syst.)^{+0.83}_{-0.57}(N_{B_s^(*)\bar B_s^(*))] \times 10^{-4}. The ratio of the two branching fractions is measured to be $\frac{Br(B_s\to J/\psi\eta')}{Br(B_s\to J/\psi \eta)} = 0.73\pm 0.14(stat.)\pm 0.02(syst.)$.Comment: 5 pages, 3 figures, 2 table

The Silicon Vertex Detector of the Belle II Experiment

The silicon vertex detector (SVD) for the Belle II experiment at the SuperKEKB accelerator in Japan is responsible for detecting particle’s origins. It comprises four cylindrical layers with ladder-like double-sided silicon detector (DSSD) arrays on each layer. The ladders produced under a stringent quality control showed good mechanical tolerance with a DSSD distortion &lt;300 µm and with an electrical efficiency &gt;99%. The SVD was commissioned with cosmic-ray events for two months. Cluster-finding efficiency was estimated in the commissioning to be &gt;98.5%. The commissioned SVD had been installed on the Belle II detector. The so-called "phase 3" of the experiment with the SVD will start in March 2019. © Copyright owned by the author(s) under the terms of the Creative Commons

Observation of New Resonant Structures in &#0947;&#0947;&#8594;&#0969;&#0981;, &#0981;&#0981;, and &#0969;&#0969;

The processes &#0947;&#0947;&#8594;&#0969;&#0981;, &#0981;&#0981;, and &#0969;&#0969; are measured using an 870&#8201;&#8201;fb&#8722;1 data sample collected with the Belle detector at the KEKB asymmetric-energy e+e&#8722; collider. Production of vector meson pairs is clearly observed and their cross sections are measured for masses that range from threshold to 4.0 GeV. In addition to signals from well established spin-zero and spin-two charmonium states, there are resonant structures below charmonium threshold, which have not been previously observed. We report a spin-parity analysis for the new structures and determine the products of the &#0951;c, &#0967;c0, and &#0967;c2 two-photon decay widths and branching fractions to &#0969;&#0981;, &#0981;&#0981;, and &#0969;&#0969;