D. Levit’s research while affiliated with High Energy Accelerator Research Organization and other places

We present a measurement of the ratio of partial branching fractions of the semileptonic inclusive decays, B ¯ → X u ℓ ν ¯ to B ¯ → X c ℓ ν ¯ , where ℓ = ( e , μ ) , using the full Belle sample of 772 × 10 6 B B ¯ pairs collected at the ϒ ( 4 S ) resonance. The identification of inclusive B ¯ → X u ℓ ν ¯ decays is difficult due to the abundance of Cabibbo–Kobayashi–Maskawa-favored B ¯ → X c ℓ ν ¯ events, which share a similar event topology. To minimize dependence on the modeling of these channels, a data-driven description of B ¯ → X c ℓ ν ¯ is employed. The ratio is measured via a two-dimensional fit to the squared four-momentum transfer to the lepton pair, and the charged lepton energy in the B meson rest frame, where the latter must be larger than 1 GeV, covering approximately 86% and 78% of the B ¯ → X u ℓ ν ¯ and B ¯ → X c ℓ ν ¯ phase space, respectively. We find Δ B ( B ¯ → X u ℓ ν ¯ ) / Δ B ( B ¯ → X c ℓ ν ¯ ) = ( 1.99 ± 0.1 7 stat ± 0.1 6 syst ) × 10 − 2 , where the uncertainties are statistical and systematic, respectively. We extract | V u b | / | V c b | using two theoretical calculations for the partial decay rate of B ¯ → X u ℓ ν ¯ , finding ( | V u b | / | V c b | ) BLNP = ( 9.81 ± 0.4 2 stat ± 0.3 8 syst ± 0.5 1 Δ Γ ( B ¯ → X u ℓ ν ¯ ) ± 0.2 0 Δ Γ ( B ¯ → X c ℓ ν ¯ ) ) × 10 − 2 and ( | V u b | / | V c b | ) GGOU = ( 10.06 ± 0.4 3 stat ± 0.3 9 syst ± 0.2 3 Δ Γ ( B ¯ → X u ℓ ν ¯ ) ± 0.2 0 Δ Γ ( B ¯ → X c ℓ ν ¯ ) ) × 10 − 2 , where the third and fourth uncertainties are from the partial decay rates of B ¯ → X u ℓ ν ¯ and B ¯ → X c ℓ ν ¯ , respectively. In addition, we report the partial branching fractions separately for charged and neutral B meson decays, and for electron and muon decay channels. We place a limit on isospin breaking in B ¯ → X u ℓ ν ¯ decays, and find no indication of lepton flavor universality violation in either the charmed or charmless mode. Furthermore, we unfold the B ¯ → X u ℓ ν ¯ and B ¯ → X c ℓ ν ¯ yields and report the differential ratio in lepton energy and four-momentum transfer squared. Published by the American Physical Society 2025

We present measurements of B + → ρ + γ and B 0 → ρ 0 γ decays using a combined data sample of 772 × 10 6 B B ¯ pairs collected by the Belle experiment and 387 × 10 6 B B ¯ pairs collected by the Belle II experiment in e + e − collisions at the ϒ ( 4 S ) resonance. After an optimized selection, a simultaneous fit to the Belle and Belle II datasets yields 114 ± 12 B + → ρ + γ and 99 ± 12 B 0 → ρ 0 γ decays. The measured branching fractions are ( 13.1 − 1.9 − 1.2 + 2.0 + 1.3 ) × 10 − 7 and ( 7.6 ± 1.3 − 0.8 + 1.0 ) × 10 − 7 for B + → ρ + γ and B 0 → ρ 0 γ decays, respectively, where the first uncertainty is statistical and the second is systematic. We also measure the isospin asymmetry A I ( B → ρ γ ) = ( 10.9 − 11.7 − 7.3 + 11.2 + 7.8 ) % and the direct C P asymmetry A C P ( B + → ρ + γ ) = ( − 8.2 ± 15.2 − 1.3 + 2.0 ) % . Published by the American Physical Society 2025

We measure the branching fraction and C P -violating flavor-dependent rate asymmetry of B 0 → π 0 π 0 decays reconstructed using the Belle II detector in an electron-positron collision sample containing 387 × 10 6 ϒ ( 4 S ) mesons. Using an optimized event selection, we find 125 ± 20 signal decays in a fit to background-discriminating and flavor-sensitive distributions. The resulting branching fraction is ( 1.25 ± 0.23 ) × 10 − 6 and the C P -violating asymmetry is 0.03 ± 0.30 . Published by the American Physical Society 2025

A bstract We report measurements of the absolute branching fractions $\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)$ , $\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)$ , and $\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right)$ , where the latter is measured for the first time. The results are based on a 121.4 fb − 1 data sample collected at the Υ(10860) resonance by the Belle detector at the KEKB asymmetric-energy e ⁺ e − collider. We reconstruct one ${B}_{s}^{0}$ meson in ${e}^{+}{e}^{-}\to \Upsilon\left(10860\right)\to {B}_{s}^{*}{\overline{B} }_{s}^{*}$ events and measure yields of ${D}_{s}^{+}$ , D ⁰ , and D ⁺ mesons in the rest of the event. We obtain $\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(68.6\pm 7.2\pm 4.0\right)\%$ , $\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(21.5\pm 6.1\pm 1.8\right)\%$ , and $\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right)=\left(12.6\pm 4.6\pm 1.3\right)\%$ , where the first uncertainty is statistical and the second is systematic. Averaging with previous Belle measurements gives $\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(63.4\pm 4.5\pm 2.2\right)\%$ and $\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(23.9\pm 4.1\pm 1.8\right)\%$ . For the ${B}_{s}^{0}$ production fraction at the Υ(10860), we find ${f}_{s}=\left({21.4}_{-1.7}^{+1.5}\right)\%$ .

In the bottomonium sector, the hindered magnetic dipole transitions between P-wave states h b ( 2 P ) → χ b J ( 1 P ) γ , J = 0 , 1, 2, are expected to be severely suppressed according to the relativized quark model, due to the spin flip of the b quark. Nevertheless, a recent model following the coupled-channel approach predicts the corresponding branching fractions to be enhanced by orders of magnitude. In this Letter, we report the first search for such transitions. We find no significant signals and set upper limits at 90% confidence level on the corresponding branching fractions: B [ h b ( 2 P ) → γ χ b 0 ( 1 P ) ] < 2.7 × 10 − 1 , B [ h b ( 2 P ) → γ χ b 1 ( 1 P ) ] < 5.4 × 10 − 3 and B [ h b ( 2 P ) → γ χ b 2 ( 1 P ) ] < 1.3 × 10 − 2 . These values help to constrain the parameters of the coupled-channel models. The results are obtained using a 121.4 fb − 1 data sample taken around s = 10.860 GeV with the Belle detector at the KEKB asymmetric-energy e + e − collider. Published by the American Physical Society 2025

We report measurements of time-dependent C P asymmetries in B 0 → K S 0 π 0 γ decays based on a data sample of ( 388 ± 6 ) × 10 6 B B ¯ events collected at the ϒ ( 4 S ) resonance with the Belle II detector. The Belle II experiment operates at the SuperKEKB asymmetric-energy e + e − collider. We measure decay-time distributions to determine C P -violating parameters S and C . We determine these parameters for two ranges of K S 0 π 0 invariant mass: m ( K S 0 π 0 ) ∈ ( 0.8 , 1.0 ) GeV / c 2 , which is dominated by B 0 → K * 0 ( → K S 0 π 0 ) γ decays, and a complementary region m ( K S 0 π 0 ) ∈ ( 0.6 , 0.8 ) ∪ ( 1.0 , 1.8 ) GeV / c 2 . Our results have improved precision as compared to previous measurements and are consistent with theory predictions. Published by the American Physical Society 2025

We report the first evidence for the h b ( 2 P ) → ϒ ( 1 S ) η transition with a significance of 3.5 standard deviations. The decay branching fraction is measured to be B [ h b ( 2 P ) → ϒ ( 1 S ) η ] = ( 7.1 − 3.2 + 3.7 ± 0.8 ) × 10 − 3 , which is noticeably smaller than expected. We also set upper limits on π 0 transitions of B [ h b ( 2 P ) → ϒ ( 1 S ) π 0 ] < 1.8 × 10 − 3 , and B [ h b ( 1 P ) → ϒ ( 1 S ) π 0 ] < 1.8 × 10 − 3 , at the 90% confidence level. These results are obtained with a 131.4 fb − 1 data sample collected near the ϒ ( 5 S ) resonance with the Belle detector at the KEKB asymmetric-energy e + e − collider. Published by the American Physical Society 2024

We measure the branching fraction and $\it CP$-violating flavor-dependent rate asymmetry of $B^{0} \to \pi^{0} \pi^{0}$ decays reconstructed using the Belle II detector in an electron-positron collision sample containing $387 \times 10^{6}$ $B\overline{B}$ pairs. Using an optimized event selection, we find $126\pm 20$ signal decays in a fit to background-discriminating and flavor-sensitive distributions. The resulting branching fraction is $(1.25 \pm 0.23)\times 10^{-6}$ and the $\it CP$-violating asymmetry is $0.03 \pm 0.30$.

We report a measurement of the e + e − → π + π − π 0 cross section in the energy range from 0.62 to 3.50 GeV using an initial-state radiation technique. We use an e + e − data sample corresponding to 191 fb − 1 of integrated luminosity, collected at a center-of-mass energy at or near the ϒ ( 4 S ) resonance with the Belle II detector at the SuperKEKB collider. Signal yields are extracted by fitting the two-photon mass distribution in e + e − → π + π − π 0 γ events, which involve a π 0 → γ γ decay and an energetic photon radiated from the initial state. Signal efficiency corrections with an accuracy of 1.6% are obtained from several control data samples. The uncertainty on the cross section at the ω and ϕ resonances is dominated by the systematic uncertainty of 2.2%. The resulting cross sections in the 0.62–1.80 GeV energy range yield a μ 3 π = [ 48.91 ± 0.23 ( stat ) ± 1.07 ( syst ) ] × 10 − 10 for the leading-order hadronic vacuum polarization contribution to the muon anomalous magnetic moment. This result differs by 2.5 standard deviations from the most precise current determination. Published by the American Physical Society 2024

We present a search for the baryon number B and lepton number L violating decays τ − → Λ π − and τ − → Λ ¯ π − produced from the e + e − → τ + τ − process, using a 364 fb − 1 data sample collected by the Belle II experiment at the SuperKEKB collider. No evidence of signal is found in either decay mode, which have | Δ ( B − L ) | equal to 2 and 0, respectively. Upper limits at 90% credibility level on the branching fractions of τ − → Λ π − and τ − → Λ ¯ π − are determined to be 4.7 × 10 − 8 and 4.3 × 10 − 8 , respectively. Published by the American Physical Society 2024