Explore the vast range of titles available.

A bstract Using a data sample of 980 fb − 1 collected with the Belle detector at the KEKB asymmetric-energy e + e − collider, we study for the first time the singly Cabibbo-suppressed decays Ω c 0 → Ξ − π + and Ω − K + and the doubly Cabibbo-suppressed decay Ω c 0 → Ξ − K + . Evidence for an Ω c 0 signal in the Ω c 0 → Ξ − π + mode is reported with a significance of 4 . 5 σ including systematic uncertainties. The ratio of branching fractions to the normalization mode Ω c 0 → Ω − π + is measured to be B Ω c 0 → Ξ − π + / B Ω c 0 → Ω − π + = 0.253 ± 0.052 stat . ± 0.030 syst . . No significant signals of Ω c 0 → Ξ − K + and Ω − K + modes are found. The upper limits at 90% confidence level on ratios of branching fractions are determined to be B Ω c 0 → Ξ − K + / B Ω c 0 → Ω − π + < 0.070 and B Ω c 0 → Ω − K + / B Ω c 0 → Ω − π + < 0.29 .

The electromagnetic calorimeter of the BELLE II detector for experiments at Super B-factory SuperKEKB is briefly described. The project of the calorimeter upgrade to meet severe background conditions expected at the upgraded KEK B factory is presented.

A bstract We report the first measurement of the inclusive e + e − → b b ¯ → D s ± X and e + e − → b b ¯ → D 0 / D ¯ 0 X cross sections in the energy range from 10 . 63 to 11 . 02 GeV. Based on these results, we determine σ ( e + e − → B s 0 B ¯ s 0 X ) and σ ( e + e − → B B ¯ X ) in the same energy range. We measure the fraction of B s 0 events at Υ(10860) to be f s = ( 22.0 − 2.1 + 2.0 )%. We determine also the ratio of the B s 0 inclusive branching fractions B ( B s 0 → D 0 / D ¯ 0 X ) / B ( B s 0 → D s ± X ) = 0 . 416 ± 0 . 018 ± 0 . 092. The results are obtained using the data collected with the Belle detector at the KEKB asymmetric-energy e + e − collider.

A bstract Using a data sample of 980 fb − 1 collected with the Belle detector at the KEKB asymmetric-energy e + e − collider, we study the processes of Ξ c 0 → Λ K ¯ ∗ 0 , Ξ c 0 → Σ 0 K ¯ ∗ 0 , and Ξ c 0 → Σ + K ∗ − for the first time. The relative branching ratios to the normalization mode of Ξ c 0 → Ξ − π + are measured to be B Ξ c 0 → Λ K ¯ ∗ 0 / B Ξ c 0 → Ξ − π + = 0.18 ± 0.02 stat . ± 0.01 syst . , B Ξ c 0 → Σ 0 K ¯ ∗ 0 / B Ξ c 0 → Ξ − π + = 0.69 ± 0.03 stat . ± 0.03 syst . , B Ξ c 0 → Σ + K ∗ − / B Ξ c 0 → Ξ − π + = 0.34 ± 0.06 stat . ± 0.02 syst . , where the uncertainties are statistical and systematic, respectively. We obtain B Ξ c 0 → Λ K ¯ ∗ 0 = 3.3 ± 0.3 stat . ± 0.2 syst . ± 1.0 ref . × 10 − 3 , B Ξ c 0 → Σ 0 K ¯ ∗ 0 = 12.4 ± 0.5 stat . ± 0.5 syst . ± 3.6 ref . × 10 − 3 , B Ξ c 0 → Σ + K ∗ 0 = 6.1 ± 1.0 stat . ± 0.4 syst . ± 1.8 ref . × 10 − 3 , where the uncertainties are statistical, systematic, and from B Ξ c 0 → Ξ − π + , respectively. The asymmetry parameters α Ξ c 0 → Λ K ¯ ∗ 0 and α Ξ c 0 → Σ + K ∗ − are 0 . 15 ± 0 . 22(stat . ) ± 0 . 04(syst . ) and − 0 . 52 ± 0 . 30(stat . ) ± 0 . 02(syst . ), respectively, where the uncertainties are statistical followed by systematic.

We report measurements of charmonia produced in two-photon collisions and decaying to four-meson final states, where the meson is either a charged pion or a charged kaon. The analysis is based on a 395 fb -1 data sample accumulated with the Belle detector at the KEKB electron–positron collider. We observe signals for the three C-even charmonia η c (1S), χ c0 (1P) and χ c2 (1P) in the π + π - π + π - , K + K - π + π - and K + K - K + K - decay modes. No clear signals for η c (2S) production are found in these decay modes. We have also studied resonant structures in charmonium decays to two-body intermediate meson resonances. We report the products of the two-photon decay width and the branching fractions, , for each of the charmonium decay modes.

A bstract We report a search for the lepton-flavor-violating decays τ ± → ℓ ± α ( ℓ = e , μ ), where α is an undetected spin-0 particle, such as an axion-like particle using 736 × 10 6 tau lepton pairs collected by the Belle detector at the KEKB asymmetric-energy e + e − collider. We find no evidence of signal and obtain the most stringent upper limits on the branching fractions at 95% confidence level: ( τ ± → e ± α ) < (0.4–6.4) × 10 − 4 and ( τ ± → μ ± α ) < (0.2–3.5) × 10 − 4 at 95% confidence level for an α mass in the range 0.0 ≤ m α ≤ 1.6 GeV/ c 2 .

A bstract Using data samples of 983.0 fb − 1 and 427.9 fb − 1 accumulated with the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energy e + e − colliders, singly Cabibbo-suppressed decays Ξ c + → p K S 0 , Ξ c + → Λ π + , and Ξ c + → Σ 0 π + are observed for the first time. The ratios of branching fractions of Ξ c + → p K S 0 , Ξ c + → Λ π + , and Ξ c + → Σ 0 π + relative to that of Ξ c + → Ξ − π + π + are measured to be B Ξ c + → p K S 0 B Ξ c + → Ξ − π + π + = 2.47 ± 0.16 ± 0.07 % , B Ξ c + → Λ π + B Ξ c + → Ξ − π + π + = 1.56 ± 0.14 ± 0.09 % , B Ξ c + → Σ 0 π + B Ξ c + → Ξ − π + π + = 4.13 ± 0.26 ± 0.22 % . Multiplying these values by the branching fraction of the normalization channel, B Ξ c + → Ξ − π + π + = 2.9 ± 1.3 % , the absolute branching fractions are determined to be B Ξ c + → p K S 0 = 7.16 ± 0.46 ± 0.20 ± 3.21 × 10 − 4 , B Ξ c + → Λ π + = 4.52 ± 0.41 ± 0.26 ± 2.03 × 10 − 4 , B Ξ c + → Σ 0 π + = 1.20 ± 0.08 ± 0.07 ± 0.54 × 10 − 3 . The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty in B Ξ c + → Ξ − π + π + .

We report a measurement of the amplitude ratio $r_S$ of $B^0 \\to D^0K^{\\ast 0}$ and $B^0 \\to \\bar {D^0}K^{\\ast 0}$ decays with a Dalitz analysis of $D\\to K_S^0\\pi ^+\\pi ^-$ decays, for the first time using a model-independent method. We set an upper limit $r_S < 0.87$ at the 68% confidence level, using the full data sample of $711\\,{\\rm fb}^{-1}$ corresponding to $772\\times 10^6$$B\\bar {B}$ pairs collected at the $\\Upsilon (4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. This result is obtained from observables $x_- = +0.4 ^{+1.0 +0.0}_{-0.6 -0.1} \\pm 0.0$, $y_- = -0.6 ^{+0.8 +0.1}_{-1.0 -0.0} \\pm 0.1$, $x_+ = +0.1 ^{+0.7 +0.0}_{-0.4 -0.1} \\pm 0.1$, and $y_+ = +0.3 ^{+0.5 +0.0}_{-0.8 -0.1} \\pm 0.1$, where $x_\\pm = r_S \\cos (\\delta _S \\pm \\phi _3)$, $y_\\pm = r_S \\sin (\\delta _S \\pm \\phi _3)$, and $\\phi _3\\ (\\delta _S)$ is the weak (strong) phase difference between $B^0 \\to D^0K^{\\ast 0}$ and $B^0 \\to \\bar {D^0}K^{\\ast 0}$.

A bstract We present the results of a search for charged-lepton-flavor violating decaysτ ⁻→ ℓ⁻K_(s)⁰, where ℓ − is either an electron or a muon. We combine e + e − data samples recorded by the Belle II experiment at the SuperKEKB collider (428 fb − 1 ) with samples recorded by the Belle experiment at the KEKB collider (980 fb − 1 ) to obtain a sample of 1.3 billion e + e − → τ + τ − events. We observe 0 and 1 events and set 90% confidence level upper limits of 0 . 8 × 10 − 8 and 1 . 2 × 10 − 8 on the branching fractions of the decay modesτ ⁻→ e⁻K_(S)⁰andτ ⁻→ μ ⁻K_(S)⁰, respectively. These are the most stringent upper limits to date.

A bstract We present a measurement of the time-dependent CP asymmetry in decays using a data set of 365 fb − 1 recorded by the Belle II experiment and the final data set of 711 fb − 1 recorded by the Belle experiment at the Υ(4S) resonance. The direct and mixing-induced time-dependent CP violation parameters C and S are determined along with two additional quantities, S + and S − , defined in the two halves of the plane. The measured values are C = − 0 . 17 ± 0 . 09 ± 0 . 04, S = − 0 . 29 ± 0 . 11 ± 0 . 05, S + = −0 . 57 ± 0 . 23 ± 0 . 10 and S − = 0 . 31 ± 0 . 24 ± 0 . 05, where the first uncertainty is statistical and the second systematic.