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The Belle II Theory Interface Platform (B2TiP) was created as a physics prospects working group of the Belle II collaboration in June 2014. It offered a platform where theorists and experimentalists could work together to elucidate the potential impacts of the Belle II program, which includes a wide scope of physics topics: B physics, charm, τ, quarkonium physics, electroweak precision measurements, and dark sector searches.

A bstract We study the processes χ bJ ω and χ bJ ( π + π − π 0 ) non −ω ( J = 0, 1, 2) at center-of-mass energies from 10.73 to 11.02 GeV using a 142 . 5 fb − 1 data sample collected with the Belle detector at the KEKB asymmetric-energy e + e − collider; and at GeV using a 19 . 8 fb − 1 sample collected with Belle II at SuperKEKB. We find that the Υ(10753) state decays into χ bJ ω but not into χ bJ ( π + π − π 0 ) non −ω , while the Υ(10860) state, in contrast, decays into χ bJ ( π + π − π 0 ) non −ω but not into χ bJ ω . The mass and width of the Υ(10753) state are measured to be (10756 . 1 ± 3 . 4(stat . ) ± 2 . 7(syst . )) MeV/ c 2 and (32 . 2 ± 11 . 3(stat . ) ± 14 . 9(syst . )) MeV. The products of the partial width to e + e − and branching fractions for Υ(10753) → χ b 1 ω and Υ(10753) → χ b 2 ω are (1 . 57 ± 0 . 27(stat . ) ± 0 . 22(syst . )) eV and (1 . 39 ± 0 . 41(stat . ) ± 0 . 33(syst . )) eV.

A bstract We present measurements of B → K * (892) γ decays using 365 fb − 1 of data collected from 2019 to 2022 by the Belle II experiment at the SuperKEKB asymmetric-energy e + e − collider. The data sample contains (387 ± 6) × 10 6 Υ(4 S ) events. We measure branching fractions ( ) and CP asymmetries ( ) for both B 0 → K *0 γ and B + → K *+ γ decays. The difference in CP asymmetries ( ) and the isospin asymmetry (∆ 0+ ) between these neutral and charged channels are also measured. We obtain the following branching fractions and CP asymmetries: , , , and . The measured difference in CP asymmetries is , and the measured isospin asymmetry is ∆ 0+ = (+4.8 ± 2.0 ± 1.8)%. The first uncertainties listed are statistical and the second are systematic. These results are consistent with world-average values and theory predictions.

A bstract We present the result of a search for the charged-lepton-flavor violating decays τ − → e ∓ ℓ ± ℓ − , where ℓ is a muon or an electron, using a data sample with an integrated luminosity of 428 fb − 1 recorded by the Belle II experiment at the SuperKEKB e + e − collider. The selection of e + e − → τ + τ − events containing a signal candidate is based on an inclusive-tagging reconstruction and on a boosted decision tree to suppress background. Upper limits on the branching fractions between 1.3 and 2.5 × 10 − 8 are set at the 90% confidence level. These results are the most stringent bounds to date for four of the modes.

A bstract We report a search for an axion-like particle a in B → K (*) a decays using data collected with the Belle detector at the KEKB asymmetric-energy electron-positron collider. The search is based on a 711 fb − 1 data sample collected at the Υ(4 S ) resonance energy, corresponding to a sample of 772 × 10 6 Υ(4 S ) events. In this study, we search for the decay of the axion-like particle into a pair of photons, a → γγ . We scan the two-photon invariant mass in the range 0 . 16 GeV–4 . 50 GeV for the K modes and 0 . 16 GeV–4 . 20 GeV for the K * modes. No significant signal is observed in any of the modes, and 90% confidence level upper limits are established on the coupling to the W boson, g aW , as a function of a mass. The limits range from 3 × 10 − 6 GeV − 1 to 3 × 10 − 5 GeV − 1 , improving the current constraints on g aW by a factor of two over the most stringent previous experimental results.

A bstract We report results from a study of B ± → DK ± decays followed by D decaying to the CP -even final state K + K − and CP-odd final state K S 0 π 0 , where D is an admixture of D 0 and D ¯ 0 states. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle ϕ 3 . The results are based on a combined analysis of the final data set of 772 × 10 6 B B ¯ pairs collected by the Belle experiment and a data set of 198 × 10 6 B B ¯ pairs collected by the Belle II experiment, both in electron-positron collisions at the Υ(4 S ) resonance. We measure the CP asymmetries to be A CP + = (+12.5 ± 5.8 ± 1.4)% and A CP− = ( − 16.7 ± 5.7 ± 0.6)%, and the ratios of branching fractions to be R CP + = 1.164 ± 0.081 ± 0.036 and R CP− = 1.151 ± 0.074 ± 0.019. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries A CP + and A CP− have similar magnitudes and opposite signs; their difference corresponds to 3.5 standard deviations. From these values we calculate 68.3% confidence intervals of (8.5 ° < ϕ 3 < 16.5 ° ) or (84.5 ° < ϕ 3 < 95.5 ° ) or (163.3 ° < ϕ 3 < 171.5 ° ) and 0.321 < r B < 0.465.

A bstract We present the results of a search for charged-lepton-flavor violating decays , where ℓ − is either an electron or a muon. We combine e + e − data samples recorded by the Belle II experiment at the SuperKEKB collider (428 fb − 1 ) with samples recorded by the Belle experiment at the KEKB collider (980 fb − 1 ) to obtain a sample of 1.3 billion e + e − → τ + τ − events. We observe 0 and 1 events and set 90% confidence level upper limits of 0 . 8 × 10 − 8 and 1 . 2 × 10 − 8 on the branching fractions of the decay modes and , respectively. These are the most stringent upper limits to date.

A bstract We present the results of a search for charged-lepton-flavor violating decaysτ ⁻→ ℓ⁻K_(s)⁰, where ℓ − is either an electron or a muon. We combine e + e − data samples recorded by the Belle II experiment at the SuperKEKB collider (428 fb − 1 ) with samples recorded by the Belle experiment at the KEKB collider (980 fb − 1 ) to obtain a sample of 1.3 billion e + e − → τ + τ − events. We observe 0 and 1 events and set 90% confidence level upper limits of 0 . 8 × 10 − 8 and 1 . 2 × 10 − 8 on the branching fractions of the decay modesτ ⁻→ e⁻K_(S)⁰andτ ⁻→ μ ⁻K_(S)⁰, respectively. These are the most stringent upper limits to date.

We perform the first search for CP violation in$$ {D}_{(s)}^{+}\\to {K}_S^0{K}^{-}{\\pi}^{+}{\\pi}^{+} $$D s + → K S 0 K − π + π + decays. We use a combined data set from the Belle and Belle II experiments, which study e + e − collisions at center-of-mass energies at or near the Υ(4 S ) resonance. We use 980 fb − 1 of data from Belle and 428 fb − 1 of data from Belle II. We measure six CP -violating asymmetries that are based on triple products and quadruple products of the momenta of final-state particles, and also the particles’ helicity angles. We obtain a precision at the level of 0.5% for$$ {D}^{+}\\to {K}_S^0{K}^{-}{\\pi}^{+}{\\pi}^{+} $$D + → K S 0 K − π + π + decays, and better than 0.3% for$$ {D}_s^{+}\\to {K}_S^0{K}^{-}{\\pi}^{+}{\\pi}^{+} $$D s + → K S 0 K − π + π + decays. No evidence of CP violation is found. Our results for the triple-product asymmetries are the most precise to date for singly-Cabibbo-suppressed D + decays. Our results for the other asymmetries are the first such measurements performed for charm decays.

A bstract We perform the first search for CP violation in D s + → K S 0 K − π + π + decays. We use a combined data set from the Belle and Belle II experiments, which study e + e − collisions at center-of-mass energies at or near the Υ(4 S ) resonance. We use 980 fb − 1 of data from Belle and 428 fb − 1 of data from Belle II. We measure six CP -violating asymmetries that are based on triple products and quadruple products of the momenta of final-state particles, and also the particles’ helicity angles. We obtain a precision at the level of 0.5% for D + → K S 0 K − π + π + decays, and better than 0.3% for D s + → K S 0 K − π + π + decays. No evidence of CP violation is found. Our results for the triple-product asymmetries are the most precise to date for singly-Cabibbo-suppressed D + decays. Our results for the other asymmetries are the first such measurements performed for charm decays.