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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 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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Free, publicly-accessible full text available January 1, 2026
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

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