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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 dark leptophilic scalar produced in association with $τ^{+} τ^{-}$ pair in $e^{+} e^{-}$ annihilation at center-of-mass energies near 10.58 GeV

https://doi.org/10.1103/PhysRevD.109.032002

Biswas, D; Banerjee, Sw; Adachi, I; Aihara, H; Asner, D M; Aushev, T; Ayad, R; Babu, V; Behera, P; Bennett, J; et al (February 2024, Physical Review D)

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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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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 Rare $b \to d ℓ^{+} ℓ^{-}$ Transitions at Belle

https://doi.org/10.1103/PhysRevLett.133.101804

Adachi, I; Aggarwal, L; Aihara, H; Akopov, N; Aloisio, A; Al_Said, S; Asner, D M; Atmacan, H; Aushev, V; Aversano, M; et al (September 2024, Physical Review Letters)

We present the results of a search for the $b \to d ℓ^{+} ℓ^{-}$ flavor-changing neutral-current rare decays $B^{+, 0} \to (η, ω, π^{+, 0}, ρ^{+, 0}) e^{+} e^{-}$ and $B^{+, 0} \to (η, ω, π^{0}, ρ^{+}) μ^{+} μ^{-}$ using a $711 {fb}^{- 1}$ data sample that contains $772 \times 10^{6} B \bar{B}$ events. The data were collected at the $ϒ (4 S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider. We find no evidence for signal and set upper limits on branching fractions at the 90% confidence level in the range $(3.8 - 47) \times 10^{- 8}$ depending on the decay channel. The obtained limits are the world’s best results. This is the first search for the channels $B^{+, 0} \to (ω, ρ^{+, 0}) e^{+} e^{-}$ and $B^{+, 0} \to (ω, ρ^{+}) μ^{+} μ^{-}$ . Published by the American Physical Society2024
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Search for $$ {\textrm{B}}_{\textrm{s}}^0 $$ → ℓ∓τ± with the semi-leptonic tagging method at Belle

https://doi.org/10.1007/JHEP08(2023)178

Nayak, L; Nishida, S; Giri, A; Adachi, I; Aihara, H; Asner, D M; Atmacan, H; Aulchenko, V; Aushev, T; Ayad, R; et al (August 2023, Journal of High Energy Physics)

A<sc>bstract</sc> We present a search for the lepton-flavor-violating decays$$ {B}_s^0 $$ $B_{s}^{0}$ →ℓ^∓τ^±, whereℓ=e, μ, using the full data sample of 121 fb⁻¹collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energye⁺e⁻collider. We use$$ {B}_s^0{\overline{B}}_s^0 $$ $B_{s}^{0} {\bar{B}}_{s}^{0}$ events in which one$$ {B}_s^0 $$ $B_{s}^{0}$ meson is reconstructed in a semileptonic decay mode and the other in the signal mode. We find no evidence for$$ {B}_s^0 $$ $B_{s}^{0}$ → ℓ^∓τ^±decays and set upper limits on their branching fractions at 90% confidence level as$$ \mathcal{B} $$ $B$ ($$ {B}_s^0 $$ $B_{s}^{0}$ → e^∓τ^±)<14×10⁻⁴and$$ \mathcal{B} $$ $B$ ($$ {B}_s^0 $$ $B_{s}^{0}$ → μ^∓τ^±)<7.3×10⁻⁴. Our result represents the first upper limit on the$$ {B}_s^0 $$ $B_{s}^{0}$ → e^∓τ^±decay rate.
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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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Search for the Lepton Flavor Violating Decays $B^{+} \to K^{+} τ^{\pm} ℓ^{\mp}$ ( $ℓ = e$ , $μ$ ) at Belle

https://doi.org/10.1103/PhysRevLett.130.261802

Watanuki, S.; de Marino, G.; Trabelsi, K.; Adachi, I.; Aihara, H.; Asner, D. M.; Atmacan, H.; Aulchenko, V.; Aushev, T.; Ayad, R.; et al (June 2023, Physical Review Letters)

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Search for lepton-flavor-violating τ− → μ−μ+μ− decays at Belle II

https://doi.org/10.1007/JHEP09(2024)062

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

A<sc>bstract</sc> We present the result of a search for the charged-lepton-flavor violating decayτ⁻→μ⁻μ⁺μ⁻using a 424 fb⁻¹sample of data recorded by the Belle II experiment at the SuperKEKBe⁺e⁻collider. The selection ofe⁺e⁻→τ⁺τ⁻events is based on an inclusive reconstruction of the non-signal tau decay, and on a boosted decision tree to suppress background. We observe one signal candidate, which is compatible with the expectation from background processes. We set a 90% confidence level upper limit of 1.9×10⁻⁸on the branching fraction of theτ⁻→ μ⁻μ⁺μ⁻decay, which is the most stringent bound to date.
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Search for the decay $B^{0} \to K^{* 0} τ^{+} τ^{-}$ at the Belle experiment

https://doi.org/10.1103/PhysRevD.108.L011102

Dong, T V; Luo, T; Adachi, I; Aihara, H; Asner, D M; Atmacan, H; Aulchenko, V; Aushev, T; Ayad, R; Babu, V; et al (July 2023, Physical Review D)

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