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Angular analysis of $B \to K^{*} e^{+} e^{-}$ in the low- $q^{2}$ region with new electron identification at Belle

https://doi.org/10.1103/PhysRevD.110.072005

Ferlewicz, D; Urquijo, P; Adachi, I; Adamczyk, K; Aihara, H; Asner, D M; Atmacan, H; Ayad, R; Babu, V; Banerjee, Sw; et al (October 2024, Physical Review D)

We perform an angular analysis of the $B \to K^{*} e^{+} e^{-}$ decay for the dielectron mass squared, $q^{2}$ , range of $0.0008 - 1.1200 {GeV}^{2} / c^{4}$ using the full Belle dataset in the $K^{* 0} \to K^{+} π^{-}$ and $K^{* +} \to K_{S}^{0} π^{+}$ channels, incorporating new methods of electron identification to improve the statistical power of the dataset. This analysis is sensitive to contributions from right-handed currents from physics beyond the Standard Model by constraining the Wilson coefficients $C_{7}^{(')}$ . We perform a fit to the $B \to K^{*} e^{+} e^{-}$ differential decay rate and measure the imaginary component of the transversality amplitude to be $A_{T}^{Im} = - 1.27 \pm 0.52 \pm 0.12$ , and the $K^{*}$ transverse asymmetry to be $A_{T}^{(2)} = 0.52 \pm 0.53 \pm 0.11$ , with $F_{L}$ and $A_{T}^{Re}$ fixed to the Standard Model values. The resulting constraints on the value of $C_{7}^{'}$ are consistent with the Standard Model within a $2 σ$ confidence interval. Published by the American Physical Society2024
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Search for two-body $B$ meson decays to $Λ^{0}$ and $Ω_{c}^{(*) 0}$

https://doi.org/10.1103/PhysRevD.110.L031102

Savinov, V; Adachi, I; Ahn, J K; Aihara, H; Asner, D M; Atmacan, H; Ayad, R; Banerjee, Sw; Bennett, J; Bessner, M; et al (August 2024, Physical Review D)

We report the results of the first search for Standard Model and baryon-number-violating two-body decays of the neutral $B$ mesons to $Λ^{0}$ and $Ω_{c}^{(*) 0}$ using $711 {fb}^{- 1}$ of data collected at the $ϒ (4 S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider. We observe no evidence of signal from any such decays and set 95% confidence-level upper limits on the products of $B^{0}$ and ${\bar{B}}^{0}$ branching fractions for these two-body decays with $B (Ω_{c}^{0} \to π^{+} Ω^{-})$ in the range between $9.5 \times 10^{- 8}$ and $31.2 \times 10^{- 8}$ . Published by the American Physical Society2024
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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 Baryon-Number-Violating Processes in $B^{-}$ Decays to the ${\bar{Ξ}}_{c}^{0} {\bar{Λ}}_{c}^{-}$ Final State

https://doi.org/10.1103/PhysRevLett.133.071802

Gu, T; Savinov, V; Adachi, I; Aihara, H; Asner, D M; Atmacan, H; Aushev, T; Ayad, R; Banerjee, Sw; Belous, K; et al (August 2024, Physical Review Letters)

We report the results of the first search for $B^{-}$ decays to the ${\bar{Ξ}}_{c}^{0} {\bar{Λ}}_{c}^{-}$ final state using $711 {fb}^{- 1}$ of data collected at the $ϒ (4 S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+} e^{-}$ collider. The results are interpreted in terms of both direct baryon-number-violating $B^{-}$ decay and $Ξ_{c}^{0} - {\bar{Ξ}}_{c}^{0}$ oscillations which follow the standard model decay $B^{-} \to Ξ_{c}^{0} {\bar{Λ}}_{c}^{-}$ . We observe no evidence for baryon number violation and set the 95% confidence-level upper limits on the ratio of baryon-number-violating and standard model branching fractions $B (B^{-} \to {\bar{Ξ}}_{c}^{0} {\bar{Λ}}_{c}^{-}) / B (B^{-} \to Ξ_{c}^{0} {\bar{Λ}}_{c}^{-})$ to be $< 2.7 %$ and on the effective angular frequency of mixing $ω$ in $Ξ_{c}^{0} - {\bar{Ξ}}_{c}^{0}$ oscillations to be $< 0.76 {ps}^{- 1}$ (equivalent to $τ_{mix} > 1.3 ps$ ). Published by the American Physical Society2024
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Measurements of the Branching Fraction, Polarization, and $C P$ Asymmetry for the Decay $B^{0} \to ω ω$

https://doi.org/10.1103/PhysRevLett.133.081801

Guan, Y; Schwartz, A J; Kinoshita, K; Adachi, I; Aihara, H; Al_Said, S; Asner, D M; Atmacan, H; Ayad, R; Bahinipati, S; et al (August 2024, Physical Review Letters)

We present a comprehensive study of $B^{0} \to ω ω$ decays using $772 \times 10^{6} B \bar{B}$ pairs collected with the Belle detector at the KEKB $e^{+} e^{-}$ collider. This process is a suppressed charmless decay into two vector mesons and can exhibit interesting polarization and $C P$ violation. The decay is observed for the first time with a significance of 7.9 standard deviations. We measure a branching fraction $B = (1.53 \pm 0.29 \pm 0.17) \times 10^{- 6}$ , a fraction of longitudinal polarization $f_{L} = 0.87 \pm 0.13 \pm 0.13$ , and a time-integrated $C P$ asymmetry $A_{C P} = - 0.44 \pm 0.43 \pm 0.11$ , where the first uncertainties listed are statistical and the second are systematic. This is the first observation of $B^{0} \to ω ω$ and the first measurements of $f_{L}$ and $A_{C P}$ for this decay. 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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Search for the decay $B_{s}^{0} \to J / ψ π^{0}$ at Belle experiment

https://doi.org/10.1103/PhysRevD.109.032007

Kumar, D; Bhuyan, B; Aihara, H; Asner, D M; Aushev, T; Ayad, R; Babu, V; Banerjee, Sw; Bauer, M; Behera, P; et al (February 2024, Physical Review D)

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Search for charged-lepton flavor violation in Υ(2S) → ℓ∓τ± (ℓ = e, μ) decays at Belle

https://doi.org/10.1007/JHEP02(2024)187

Dhamija, R; Nishida, S; Giri, A; Adachi, I; Aihara, H; Asner, D M; Aushev, T; Ayad, R; Babu, V; Bahinipati, S; et al (February 2024, Journal of High Energy Physics)

A<sc>bstract</sc> We report a search for the charged-lepton flavor violation in Υ(2S) →ℓ^∓τ^±(ℓ=e, μ) decays using a 25 fb⁻¹Υ(2S) sample collected by the Belle detector at the KEKBe⁺e⁻asymmetric-energy collider. We find no evidence for a signal and set upper limits on the branching fractions ($$ \mathcal{B} $$ $B$ ) at 90% confidence level. We obtain the most stringent upper limits:$$ \mathcal{B} $$ $B$ (Υ(2S)→ μ^∓τ^±)<0.23×10⁻⁶and$$ \mathcal{B} $$ $B$ (Υ(2S)→ e^∓τ^±)<1.12×10⁻⁶.
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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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