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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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Measurement of the integrated luminosity of data samples collected during 2019-2022 by the Belle II experiment*

https://doi.org/10.1088/1674-1137/ad806c

Adachi, I; Aggarwal, L; Ahmed, H; Ahn, J K; Aihara, H; Akopov, N; Aloisio, A; Althubiti, N; Anh_Ky, N; Asner, D M; et al (January 2025, Chinese Physics C)

Abstract A series of data samples was collected with the Belle II detector at the SuperKEKB collider from March 2019 to June 2022. We determine the integrated luminosities of these data samples using three distinct methodologies involving Bhabha (), digamma (), and dimuon () events. The total integrated luminosity obtained with Bhabha, digamma, and dimuon events is (426.88 ± 0.03 ± 2.61) fb⁻¹, (429.28 ± 0.03 ± 2.62) fb⁻¹, and (423.99 ± 0.04 ± 3.83) fb⁻¹, where the first uncertainties are statistical and the second are systematic. The resulting total integrated luminosity obtained from the combination of the three methods is (427.87 ± 2.01) fb⁻¹.
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Free, publicly-accessible full text available January 1, 2026
Observation of charmed strange meson pair production in $ϒ (2 S)$ decays and in $e^{+} e^{-}$ annihilation at $\sqrt{s} = 10.52 GeV$

https://doi.org/10.1103/PhysRevD.108.112015

Gao, B S; Zhu, W J; Wang, X L; Adachi, I; Aihara, H; Asner, D M; Aulchenko, V; Aushev, T; Ayad, R; Babu, V; et al (December 2023, Physical Review D)

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Search for the baryon number and lepton number violating decays $τ^{-} \to Λ π^{-}$ and $τ^{-} \to \bar{Λ} π^{-}$ at Belle II

https://doi.org/10.1103/PhysRevD.110.112003

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

We present a search for the baryon number $B$ and lepton number $L$ violating decays $τ^{-} \to Λ π^{-}$ and $τ^{-} \to \bar{Λ} π^{-}$ produced from the $e^{+} e^{-} \to τ^{+} τ^{-}$ 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 $τ^{-} \to Λ π^{-}$ and $τ^{-} \to \bar{Λ} π^{-}$ are determined to be $4.7 \times 10^{- 8}$ and $4.3 \times 10^{- 8}$ , respectively. Published by the American Physical Society2024
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Free, publicly-accessible full text available December 1, 2025
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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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 the double-charmonium state with ηcJ/ψ at Belle

https://doi.org/10.1007/JHEP08(2023)121

Yin, J H; Li, Y B; Won, E; Adachi, I; Aihara, H; Al_Said, S; Asner, D M; Aushev, T; Ayad, R; Babu, V; et al (August 2023, Journal of High Energy Physics)

A<sc>bstract</sc> We measure the cross section ofe⁺e⁻→η_cJ/ψat the Υ(nS)(n= 1–5) on-resonance and 10.52 GeV off-resonance energy points using the full data sample collected by the Belle detector with an integrated luminosity of 955 fb⁻¹. We also search for double charmonium production ine⁺e⁻→η_cJ/ψvia initial state radiation near theη_cJ/ψthreshold. No evident signal of the double charmonium state is found, but evidence for thee⁺e⁻→ η_cJ/ψprocess is found with a statistical significance greater than 3.3σnear theη_cJ/ψthreshold. The average cross section near the threshold is measured and upper limits of cross sections are set for other regions.
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Measurement of the energy dependence of the e+e− → $$ B\overline{B} $$, $$ B{\overline{B}}^{\ast } $$, and $$ {B}^{\ast }{\overline{B}}^{\ast } $$ cross sections at Belle II

https://doi.org/10.1007/JHEP10(2024)114

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

A<sc>bstract</sc> We report measurements of thee⁺e⁻→$$ B\overline{B} $$ $B \bar{B}$ ,$$ B{\overline{B}}^{\ast } $$ $B {\bar{B}}^{*}$ , and$$ {B}^{\ast }{\overline{B}}^{\ast } $$ $B^{*} {\bar{B}}^{*}$ cross sections at four energies, 10653, 10701, 10746 and 10805 MeV, using data collected by the Belle II experiment. We reconstruct oneBmeson in a large number of hadronic final states and use its momentum to identify the production process. In the first 2 – 5 MeV above$$ {B}^{\ast }{\overline{B}}^{\ast } $$ $B^{*} {\bar{B}}^{*}$ threshold, thee⁺e⁻→$$ {B}^{\ast }{\overline{B}}^{\ast } $$ $B^{*} {\bar{B}}^{*}$ cross section increases rapidly. This may indicate the presence of a pole close to the threshold.
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