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A bstract A comprehensive set of azimuthal single-spin and double-spin asymmetries in semi-inclusive leptoproduction of pions, charged kaons, protons, and antiprotons from transversely polarized protons is presented. These asymmetries include the previously published HERMES results on Collins and Sivers asymmetries, the analysis of which has been extended to include protons and antiprotons and also to an extraction in a three-dimensional kinematic binning and enlarged phase space. They are complemented by corresponding results for the remaining four single-spin and four double-spin asymmetries allowed in the one-photon-exchange approximation of the semi-inclusive deep-inelastic scattering process for target-polarization orientation perpendicular to the direction of the incoming lepton beam. Among those results, significant non-vanishing cos ( ϕ−ϕ S ) modulations provide evidence for a sizable worm-gear (II) distribution, g 1 T q x p T 2 . Most of the other modulations are found to be consistent with zero with the notable exception of large sin ( ϕ S ) modulations for charged pions and K + .

Abstract The Aerogel Ring Imaging Cherenkov (ARICH) counter serves as a particle identification device in the forward end-cap region of the Belle II spectrometer. It is capable of identifying pions and kaons with momenta up to $4\\>$GeV$\\>$c$^{-1}$ by detecting Cherenkov photons emitted in the silica aerogel radiator. After the detector alignment and calibration of the probability density function, we evaluate the performance of the ARICH counter using early beam collision data. Event samples of $D^{\\ast +} \\to D^0 \\pi^+ (D^0 \\to K^-\\pi^+)$ were used to determine the $\\pi(K)$ efficiency and the $K(\\pi)$ misidentification probability. We found that the ARICH counter is capable of separating kaons from pions with an identification efficiency of $93.5 \\pm 0.6 \\, \\%$ at a pion misidentification probability of $10.9 \\pm 0.9 \\, \\%$. This paper describes the identification method of the counter and the evaluation of the performance during its early operation.

A bstract Using data samples of 983.0 fb − 1 and 427.9 fb − 1 accumulated with the Belle and Belle II detectors operating at the KEKB and SuperKEKB asymmetric-energy e + e − colliders, singly Cabibbo-suppressed decays Ξ c + → p K S 0 , Ξ c + → Λ π + , and Ξ c + → Σ 0 π + are observed for the first time. The ratios of branching fractions of Ξ c + → p K S 0 , Ξ c + → Λ π + , and Ξ c + → Σ 0 π + relative to that of Ξ c + → Ξ − π + π + are measured to be B Ξ c + → p K S 0 B Ξ c + → Ξ − π + π + = 2.47 ± 0.16 ± 0.07 % , B Ξ c + → Λ π + B Ξ c + → Ξ − π + π + = 1.56 ± 0.14 ± 0.09 % , B Ξ c + → Σ 0 π + B Ξ c + → Ξ − π + π + = 4.13 ± 0.26 ± 0.22 % . Multiplying these values by the branching fraction of the normalization channel, B Ξ c + → Ξ − π + π + = 2.9 ± 1.3 % , the absolute branching fractions are determined to be B Ξ c + → p K S 0 = 7.16 ± 0.46 ± 0.20 ± 3.21 × 10 − 4 , B Ξ c + → Λ π + = 4.52 ± 0.41 ± 0.26 ± 2.03 × 10 − 4 , B Ξ c + → Σ 0 π + = 1.20 ± 0.08 ± 0.07 ± 0.54 × 10 − 3 . The first and second uncertainties above are statistical and systematic, respectively, while the third ones arise from the uncertainty in B Ξ c + → Ξ − π + π + .

A bstract We present a study of Ξ c 0 → Ξ 0 π 0 , Ξ c 0 → Ξ 0 η , and Ξ c 0 → Ξ 0 η ′ decays using the Belle and Belle II data samples, which have integrated luminosities of 980 fb − 1 and 426 fb − 1 , respectively. We measure the following relative branching fractions B Ξ c 0 → Ξ 0 π 0 / B Ξ c 0 → Ξ − π + = 0.48 ± 0.02 stat ± 0.03 syst , B Ξ c 0 → Ξ 0 η / B Ξ c 0 → Ξ − π + = 0.11 ± 0.01 stat ± 0.01 syst , B Ξ c 0 → Ξ 0 η ′ / B Ξ c 0 → Ξ − π + = 0.08 ± 0.02 stat ± 0.01 syst for the first time, where the uncertainties are statistical (stat) and systematic (syst). By multiplying by the branching fraction of the normalization mode, B Ξ c 0 → Ξ − π + , we obtain the following absolute branching fraction results B Ξ c 0 → Ξ 0 π 0 = 6.9 ± 0.3 stat ± 0.5 syst ± 1.3 norm × 10 − 3 , B Ξ c 0 → Ξ 0 η = 1.6 ± 0.2 stat ± 0.2 syst ± 0.3 norm × 10 − 3 , B Ξ c 0 → Ξ 0 η ′ = 1.2 ± 0.3 stat ± 0.1 syst ± 0.2 norm × 10 − 3 , where the third uncertainties are from B Ξ c 0 → Ξ − π + . The asymmetry parameter for Ξ c 0 → Ξ 0 π 0 is measured to be α Ξ c 0 → Ξ 0 π 0 = − 0.90 ± 0.15 stat ± 0.23 syst .

A bstract We present a measurement of the ratio R μ = B τ − → μ − ν ¯ μ ν τ / B τ − → e − ν ¯ e ν τ of branching fractions B of the τ lepton decaying to muons or electrons using data collected with the Belle II detector at the SuperKEKB e + e − collider. The sample has an integrated luminosity of 362 ± 2 fb − 1 at a centre-of-mass energy of 10.58 GeV. Using an optimised event selection, a binned maximum likelihood fit is performed using the momentum spectra of the electron and muon candidates. The result, R μ = 0.9675 ± 0.0007 ± 0.0036, where the first uncertainty is statistical and the second is systematic, is the most precise to date. It provides a stringent test of the light-lepton universality, translating to a ratio of the couplings of the muon and electron to the W boson in τ decays of 0.9974 ± 0.0019, in agreement with the standard model expectation of unity.

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 report a determination of the CKM angle ϕ 3 , also known as γ , from a combination of measurements using samples of up to 711 fb − 1 from the Belle experiment and up to 362 fb − 1 from the Belle II experiment. We combine results from analyses of B + → DK + , B + → Dπ + , and B + → D * K + decays, where D is an admixture of D 0 and D ¯ 0 mesons, in a likelihood fit to obtain ϕ 3 = (75.2 ± 7.6) ° . We also briefly discuss the interpretation of this result.

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 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.