First observation of Λπ+\Lambda\pi^+ and Λπ−\Lambda\pi^- signals near the KˉN(I=1)\bar{K}N (I=1) mass threshold in Λc+→Λπ+π+π−\Lambda_c^+\rightarrow\Lambda\pi^+\pi^+\pi^- decay

Using the data sample of 980 fb$^{-1}$ collected with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we present the results of an investigation of the $\Lambda\pi^+$ and $\Lambda\pi^-$ invariant mass distributions looking for substructure in the decay $\Lambda_c^+\rightarrow\Lambda\pi^+\pi^+\pi^-$. We find a significant signal in each mass distribution. When interpreted as resonances, we find for the $\Lambda\pi^+$ ($\Lambda\pi^-$) combination a mass of $1434.3 \pm 0.6 (\mathrm{stat.}) ^{+0.9}_{-0.0}(\mathrm{syst.})$ MeV/$c^2$ ($1438.5 \pm 0.9 (\mathrm{stat.}) ^{+0.2}_{-2.5}(\mathrm{syst.})$ MeV/$c^2$), an intrinsic width of $11.5 \pm 2.8 (\mathrm{stat.}) ^{+0.1}_{-5.3}(\mathrm{syst.})$ MeV/$c^2$ ($33.0 \pm 7.5 (\mathrm{stat.}) ^{+0.1}_{-23.6}(\mathrm{syst.})$ MeV/$c^2$) with a significance of 7.5$\sigma$ (6.2$\sigma$). As these two signals are very close to the $\bar{K}N$ threshold, we also investigate the possibility of a $\bar{K}N$ cusp, and find that we cannot discriminate between these two interpretations due to the limited size of the data sample

Measurement of the branching fraction and search for CP violation in D0→Ks0Ks0π+π− decays at Belle

We measure the branching fraction for the Cabibbo-suppressed decay D0→KS0KS0π+π- and search for CP violation via a measurement of the CP asymmetry ACP as well as the T-odd triple-product asymmetry aCPT. We use 922 fb-1 of data recorded by the Belle experiment, which ran at the KEKB asymmetric-energy e+e- collider. The branching fraction is measured relative to the Cabibbo-favored normalization channel D0→KS0π+π-; the result is B(D0→KS0KS0π+π-)=[4.79±0.08(stat)±0.10(syst)±0.31(norm)]×10^-4, where the first uncertainty is statistical, the second is systematic, and the third is from uncertainty in the normalization channel. We also measure ACP=[-2.51±1.44(stat)-0.10+0.11(syst)]%, and aCPT=[-1.95±1.42(stat)-0.12+0.14(syst)]%. These results show no evidence of CP violation

Measurement of the integrated luminosity of the Phase 2 data of the Belle II experiment

From April to July 2018, a data sample at the peak energy of the γ(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 ± 0.3 ± 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

Search for the decay Bs0→J/ψπ0 at Belle experiment

We have analyzed 121.4 fb−1 of data collected at the Υ(5S) resonance by the Belle experiment using the KEKB asymmetric-energy e+e− collider to search for the decay B0s→J/ψπ0. We observe no signal and report an upper limit on the branching fraction B(B0s→J/ψπ0) of 1.21×10^−5 at 90% confidence level. This result is the most stringent, improving the previous bound by 2 orders of magnitude

Measurement of the branching fractions for Cabibbo-suppressed decays D+→K+K−π+π0 and D(s)+→K+π−π+π0 at Belle

We present measurements of the branching fractions for the singly Cabibbo-suppressed decays D+→K+K−π+π0 and D+s→K+π−π+π0, and the doubly Cabibbo-suppressed decay D+→K+π−π+π0, based on 980 fb−1 of data recorded by the Belle experiment at the KEKB e+e− collider. We measure these modes relative to the Cabibbo-favored modes D+→K−π+π+π0 and D+s→K+K−π+π0. Our results for the ratios of branching fractions are B(D+→K+K−π+π0)/B(D+→K−π+π+π0)=(11.32±0.13±0.26)%, B(D+→K+π−π+π0)/B(D+→K−π+π+π0)=(1.68±0.11±0.03)%, and B(D+s→K+π−π+π0)/B(D+s→K+K−π+π0)=(17.13±0.62±0.51)%, where the uncertainties are statistical and systematic, respectively. The second value corresponds to (5.83±0.42)×tan4θC, where θC is the Cabibbo angle; this value is larger than other measured ratios of branching fractions for a doubly Cabibbo-suppressed charm decay to a Cabibbo-favored decay. Multiplying these results by world average values for B(D+→K−π+π+π0) and B(D+s→K+K−π+π0) yields B(D+→K+K−π+π0)=(7.08±0.08±0.16±0.20)×10^−3, B(D+→K+π−π+π0)=(1.05±0.07±0.02±0.03)×10^−3, and B(D+s→K+π−π+π0)=(9.44±0.34±0.28±0.32)×10^−3, where the third uncertainty is due to the branching fraction of the normalization mode. The first two results are consistent with, but more precise than, the current world averages. The last result is the first measurement of this branching fraction

Search for a Heavy Neutrino in τ Decays at Belle

We report on a search for a heavy Majorana neutrino in the decays τ^{-}→π^{-}ν_{h}, ν_{h}→π^{±}l^{∓}, l=e, μ. The results are obtained using the full data sample of 988 fb^{-1} collected with the Belle detector at the KEKB asymmetric energy e^{+}e^{-} collider, which contains 912×10^{6} ττ pairs. We observe no significant signal and set 95% CL upper limits on the couplings of the heavy right-handed neutrinos to the conventional standard model left-handed neutrinos in the mass range 0.2-1.6 GeV/c^{2}. This is the first study of a mixed couplings of heavy neutrinos to τ leptons and light-flavor leptons

Spatial resolution of the Belle II Silicon Vertex detector

The Belle II experiment at the SuperKEKB collider in Japan will search for new sources of CP violation and indirectly probe new physics by studying the suppressed decays of beauty mesons, charm mesons and tau leptons. In these pursuits, the spatial resolution of the Belle II Silicon Vertex Detector (SVD) will play a key role. We report herein the spatial resolution of the SVD using simulated data for a simplified version of the Belle II detector

Measurement of the branching fraction of Ξc0→Λc+π− at Belle

Based on a data sample of 983 fb−1 collected with the Belle detector at the KEKB asymmetric-energy e+e− collider, we present the study of the heavy-flavor-conserving decay Ξ0c→Λ+cπ− with Λ+c reconstructed via its pK−π+ decay mode. The branching fraction ratio B(Ξ0c→Λ+cπ−)/B(Ξ0c→Ξ−π+) is measured to be 0.38±0.04±0.04. Combing with the world average value of B(Ξ0c→Ξ−π+), the branching fraction B(Ξ0c→Λ+cπ−) is deduced to be (0.54±0.05±0.05±0.12)%. Here, the uncertainties above are statistical, systematic, and from B(Ξ0c→Ξ−π+), respectively

Search for X

The branching fractions of the $\Upsilon(1S)$ inclusive decays into final states with a $J/\psi$ or a $\psi(2S)$ are measured with improved precision to be \BR(\Upsilon(1S)\to J/\psi + {\rm anything})=(5.25\pm 0.13(\mathrm{stat.})\pm 0.25(\mathrm{syst.}))\times 10^{-4} and \BR(\Upsilon(1S)\to \psi(2S) + {\rm anything})=(1.23\pm 0.17(\mathrm{stat.})\pm 0.11(\mathrm{syst.}))\times 10^{-4}. The first search for $\Upsilon(1S)$ decays into $XYZ$ states that decay into a $J/\psi$ or a $\psi(2S)$ plus one or two charged tracks yields no significant signals for $XYZ$ states in any of the examined decay modes, and upper limits on their production rates in $\Upsilon(1S)$ inclusive decays are determined.Comment: 10 pages, 7 figures, 3 table

First search for the weak radiative decays Λc+→Σ+γ and Ξc0→Ξ0γ

We present the first search for the weak radiative decays Λc+→Σ+γ and Ξc0→Ξ0γ using a data sample of 980 fb-1 collected by the Belle detector operating at the KEKB asymmetric-energy e+e- collider. There are no evident Λc+→Σ+γ or Ξc0→Ξ0γ signals. Taking the decays Λc+→pK-π+ and Ξc0→Ξ-π+ as normalization channels, the upper limits at 90% credibility level on the ratios of branching fractions B(Λc+→Σ+γ)/B(Λc+→pK-π+)<4.0×10^-3 and B(Ξc0→Ξ0γ)/B(Ξc0→Ξ-π+)<1.2×10^-2 are determined. We obtain the upper limits at 90% credibility level on the absolute branching fractions B(Λc+→Σ+γ)<2.6×10^-4 and B(Ξc0→Ξ0γ)<1.8×10^-