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Observation of time-dependent $C P$ violation and measurement of the branching fraction of $B^{0} \to J / ψ π^{0}$ decays

https://doi.org/10.1103/PhysRevD.111.012011

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

We present a measurement of the branching fraction and time-dependent charge-parity ( $C P$ ) decay-rate asymmetries in $B^{0} \to J / ψ π^{0}$ decays. The data sample was collected with the Belle II detector at the SuperKEKB asymmetric $e^{+} e^{-}$ collider in 2019–2022 and contains $(387 \pm 6) \times 10^{6} B \bar{B}$ meson pairs from $ϒ (4 S)$ decays. We reconstruct $392 \pm 24$ signal decays and fit the $C P$ parameters from the distribution of the proper-decay-time difference of the two $B$ mesons. We measure the branching fraction to be $(B^{0} \to J / ψ π^{0}) = (2.00 \pm 0.12 \pm 0.09) \times 10^{- 5}$ and the direct and mixing-induced $C P$ asymmetries to be $C_{C P} = 0.13 \pm 0.12 \pm 0.03$ and $S_{C P} = - 0.88 \pm 0.17 \pm 0.03$ , respectively, where the first uncertainties are statistical and the second are systematic. We observe mixing-induced $C P$ violation with a significance of 5.0 standard deviations for the first time in this mode. Published by the American Physical Society2025
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Search for the decay $B^{0} \to γ γ$ using Belle and Belle II data

https://doi.org/10.1103/PhysRevD.110.L031106

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

We report the result of a search for the rare decay $B^{0} \to γ γ$ using a combined dataset of $753 \times 10^{6} B \bar{B}$ pairs collected by the Belle experiment and $387 \times 10^{6} B \bar{B}$ pairs collected by the Belle II experiment from decays of the $ϒ (4 S)$ resonance produced in $e^{+} e^{-}$ collisions. A simultaneous fit to the Belle and Belle II data sets yields ${11.0}_{- 5.5}^{+ 6.5}$ signal events, corresponding to a $2.5 σ$ significance. We determine the branching fraction $B (B^{0} \to γ γ) = ({3.7}_{- 1.8}^{+ 2.2} (stat) \pm 0.5 (syst)) \times 10^{- 8}$ and set a 90% credibility level upper limit of $B (B^{0} \to γ γ) < 6.4 \times 10^{- 8}$ . Published by the American Physical Society2024
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Measurement of the absolute branching fraction of the inclusive decay ${\bar{Λ}}_{c}^{-} \to \bar{n} + X$

https://doi.org/10.1103/PhysRevD.108.L031101

Ablikim, M; Achasov, M N; Adlarson, P; Albrecht, M; Aliberti, R; Amoroso, A; An, M R; An, Q; Bai, X H; Bai, Y; et al (August 2023, Physical Review D)

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