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Measurement of Angular Coefficients of $\bar{B} \to D^{*} ℓ {\bar{ν}}_{ℓ}$ : Implications for $| V_{c b} |$ and Tests of Lepton Flavor Universality

https://doi.org/10.1103/PhysRevLett.133.131801

Prim, M T; Bernlochner, F; Metzner, F; Aihara, H; Asner, D M; Aushev, T; Ayad, R; Babu, V; Banerjee, Sw; Behera, P; et al (September 2024, Physical Review Letters)

We measure the complete set of angular coefficients $J_{i}$ for exclusive $\bar{B} \to D^{*} ℓ {\bar{ν}}_{ℓ}$ decays ( $ℓ = e$ , $μ$ ). Our analysis uses the full $711 {fb}^{- 1}$ Belle dataset with hadronic tag-side reconstruction. The results allow us to extract the form factors describing the $\bar{B} \to D^{*}$ transition and the Cabibbo-Kobayashi-Maskawa matrix element $| V_{cb} |$ . Using recent lattice QCD calculations for the hadronic form factors, we find $| V_{cb} | = (40.7 \pm 0.7) \times 10^{- 3}$ using the Boyd-Grinstein-Lebed parametrization, compatible with determinations from inclusive semileptonic decays. We search for lepton flavor universality violation as a function of the hadronic recoil parameter $w$ and investigate the differences of the electron and muon angular distributions. We find no deviation from standard model expectations. Published by the American Physical Society2024
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Search for a heavy neutral lepton that mixes predominantly with the tau neutrino

https://doi.org/10.1103/PhysRevD.109.L111102

Nayak, M; Dey, S; Soffer, A; Adachi, I; Aihara, H; Al_Said, S; Asner, D M; Atmacan, H; Ayad, R; Babu, V; et al (June 2024, Physical Review D)

We report a search for a heavy neutral lepton (HNL) that mixes predominantly with $ν_{τ}$ . The search utilizes data collected with the Belle detector at the KEKB asymmetric energy $e^{+} e^{-}$ collider. The data sample was collected at and just below the center-of-mass energies of the $ϒ (4 S)$ and $ϒ (5 S)$ resonances and has an integrated luminosity of $915 {fb}^{- 1}$ , corresponding to $(836 \pm 12) \times 10^{6}$ $e^{+} e^{-} \to τ^{+} τ^{-}$ events. We search for production of the HNL (denoted $N$ ) in the decay $τ^{-} \to π^{-} N$ followed by its decay via $N \to μ^{+} μ^{-} ν_{τ}$ . The search focuses on the parameter-space region in which the HNL is long-lived, so that the $μ^{+} μ^{-}$ originate from a common vertex that is significantly displaced from the collision point of the KEKB beams. Consistent with the expected background yield, one event is observed in the data sample after application of all the event-selection criteria. We report limits on the mixing parameter of the HNL with the $τ$ neutrino as a function of the HNL mass. Published by the American Physical Society2024
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Search for the semileptonic decays $Ξ_{c}^{0} \to Ξ^{0} ℓ^{+} ℓ^{-}$ at Belle

https://doi.org/10.1103/PhysRevD.109.052003

Cui, J X; Li, Y B; Shen, C P; Adachi, I; Aihara, H; Al_Said, S; Asner, D M; Aushev, T; Ayad, R; Babu, V; et al (March 2024, Physical Review D)

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Measurement of $C P$ Asymmetries in $B^{0} \to K_{S}^{0} π^{0} γ$ Decays at Belle II

https://doi.org/10.1103/PhysRevLett.134.011802

Adachi, I; Aggarwal, L; Ahmed, H; Aihara, H; Akopov, N; Aloisio, A; Anh_Ky, N; Asner, D M; Atmacan, H; Aushev, T; et al (January 2025, Physical Review Letters)

We report measurements of time-dependent $C P$ asymmetries in $B^{0} \to K_{S}^{0} π^{0} γ$ decays based on a data sample of $(388 \pm 6) \times 10^{6} B \bar{B}$ 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: $m (K_{S}^{0} π^{0}) \in (0.8, 1.0) GeV / c^{2}$ , which is dominated by $B^{0} \to K^{* 0} (\to K_{S}^{0} π^{0}) γ$ decays, and a complementary region $m (K_{S}^{0} π^{0}) \in (0.6, 0.8) \cup (1.0, 1.8) GeV / c^{2}$ . Our results have improved precision as compared to previous measurements and are consistent with theory predictions. Published by the American Physical Society2025
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Free, publicly-accessible full text available January 1, 2026
Measurement of $C P$ asymmetries in $B^{0} \to η^{'} K_{S}^{0}$ decays at Belle II

https://doi.org/10.1103/PhysRevD.110.112002

Adachi, I; Aggarwal, L; Ahmed, H; Aihara, H; Akopov, N; Aloisio, A; Anh_Ky, N; Asner, D M; Atmacan, H; Aushev, T; et al (December 2024, Physical Review D)

We describe a measurement of charge-parity ( $C P$ ) violation asymmetries in $B^{0} \to η^{'} K_{S}^{0}$ decays using Belle II data. We consider $η^{'} \to η (\to γ γ) π^{+} π^{-}$ and $η^{'} \to ρ (\to π^{+} π^{-}) γ$ decays. The data were collected at the SuperKEKB asymmetric-energy $e^{+} e^{-}$ collider between the years 2019 and 2022, and contain $(387 \pm 6) \times 10^{6}$ bottom-antibottom meson pairs. We reconstruct $829 \pm 35$ signal decays and extract the $C P$ violating parameters from a fit to the distribution of the proper-decay-time difference between the two $B$ mesons. The measured direct and mixing-induced $C P$ asymmetries are $C_{η^{'} K_{S}^{0}} = - 0.19 \pm 0.08 \pm 0.03$ and $S_{η^{'} K_{S}^{0}} = + 0.67 \pm 0.10 \pm 0.03$ , respectively, where the first uncertainties are statistical and the second are systematic. These results are in agreement with current world averages and standard model predictions. Published by the American Physical Society2024
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Free, publicly-accessible full text available December 1, 2025
Determination of the CKM angle ϕ3 from a combination of Belle and Belle II results

https://doi.org/10.1007/JHEP10(2024)143

Adachi, I; Aggarwal, L; Aihara, H; Akopov, N; Aloisio, A; Al_Said, S; Anh_Ky, N; Asner, D M; Atmacan, H; Aushev, V; et al (October 2024, Journal of High Energy Physics)

A<sc>bstract</sc> We report a determination of the CKM angleϕ₃, also known asγ, from a combination of measurements using samples of up to 711 fb⁻¹from the Belle experiment and up to 362 fb⁻¹from the Belle II experiment. We combine results from analyses ofB⁺→ DK⁺,B⁺→ Dπ⁺, andB⁺→ D^*K⁺decays, whereDis an admixture ofD⁰and$$ {\overline{D}}^0 $$ ${\bar{D}}^{0}$ mesons, in a likelihood fit to obtainϕ₃= (75.2±7.6)^°. We also briefly discuss the interpretation of this result.
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Search for a Heavy Neutrino in $τ$ Decays at Belle

https://doi.org/10.1103/PhysRevLett.131.211802

Liventsev, D; Adachi, I; Aihara, H; Al_Said, S; Asner, D M; Atmacan, H; Ayad, R; Babu, V; Banerjee, Sw; Bauer, M; et al (November 2023, Physical Review Letters)

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Test of lepton flavor universality with a measurement of $R (D^{*})$ using hadronic $B$ tagging at the Belle II experiment

https://doi.org/10.1103/PhysRevD.110.072020

Adachi, I; Adamczyk, K; Aggarwal, L; Ahmed, H; Aihara, H; Akopov, N; Aloisio, A; Anh_Ky, N; Asner, D M; Atmacan, H; et al (October 2024, Physical Review D)

The ratio of branching fractions $R (D^{*}) = B (\bar{B} \to D^{*} τ^{-} {\bar{ν}}_{τ}) / B (\bar{B} \to D^{*} ℓ^{-} {\bar{ν}}_{ℓ})$ , where $ℓ$ is an electron or muon, is measured using a Belle II data sample with an integrated luminosity of $189 {fb}^{- 1}$ at the SuperKEKB asymmetric-energy $e^{+} e^{-}$ collider. Data is collected at the $ϒ (4 S)$ resonance, and one $B$ meson in the $ϒ (4 S) \to B \bar{B}$ decay is fully reconstructed in hadronic decay modes. The accompanying signal $B$ meson is reconstructed as $\bar{B} \to D^{*} τ^{-} {\bar{ν}}_{τ}$ using leptonic $τ$ decays. The normalization decay, $\bar{B} \to D^{*} ℓ^{-} {\bar{ν}}_{ℓ}$ , produces the same observable final-state particles. The ratio of branching fractions is extracted in a simultaneous fit to two signal-discriminating variables in both channels and yields $R (D^{*}) = {0.262}_{- 0.039}^{+ 0.041} (stat)_{- 0.032}^{+ 0.035} (syst)$ . This result is consistent with the current world average and with Standard Model predictions. Published by the American Physical Society2024
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Search for $C P$ violation in $D_{(s)}^{+} \to K^{+} K_{S}^{0} h^{+} h^{-}$ ( $h = K$ , $π$ ) decays and observation of the Cabibbo-suppressed decay $D_{s}^{+} \to K^{+} K^{-} K_{S}^{0} π^{+}$

https://doi.org/10.1103/PhysRevD.108.L111102

Moon, H K; Won, E; Adachi, I; Aihara, H; Asner, D M; Atmacan, H; Aulchenko, V; Aushev, T; Ayad, R; Babu, V; et al (December 2023, Physical Review D)

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Study of $B^{+} \to p \bar{n} π^{0}$

https://doi.org/10.1103/PhysRevD.108.112007

Chu, K-N; Lin, Y-R; Wang, M-Z; Adachi, I; Adamczyk, K; Aihara, H; Al_Said, S; Asner, D M; Atmacan, H; Aulchenko, V; et al (December 2023, Physical Review D)

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