We present an analysis of the processes e(+)e(-) -> eta(sic)(1S), eta(sic)(2S), and gamma X-b with X-b -> pi(+) pi(-) chi(bJ), chi(bJ) -> gamma(sic)(1S) (J = 1, 2) reconstructed from gamma gamma pi(+)pi(-) l(+)l(-) (l = e; mu) final states in 19.6 fb(-1) of Belle II data collected at four energy points near the peak of the (sic)(10753) resonance. Here, X-b is a hypothetical bottomonium-sector partner of the X(3872). In the process e(+)e(-) (2S), we observe a signal with a significance that exceeds 6.0 sigma when all energy points are combined. A signal with a significance of 4.2 sigma is observed at a center-of-mass energy of 10.653 GeV, close to the B*(B) over bar* threshold. At this energy, we measure sigma(eta(sic)(2S)) /sigma(pi(+)pi(-)(2S)> 23 at the 90% confidence level, indicating a strong violation of heavy-quark spin symmetry. No significant signal is observed for e(+)e(-) -> eta(sic)(1S) or gamma X-b. Upper limits on the Born cross sections for the processes e(+)e(-) ->eta(sic)(1S) and e(+)e(-) ->gamma X-b with X-b -> pi(+)pi(-) chi(bJ) are determined.

Abstract We present a measurement of the time-dependent CP asymmetry in $${B}^{0}\to {K}_{\text{S}}^{0}{\pi }^{+}{\pi }^{-}\gamma $$ decays using a data set of 365 fb −1 recorded by the Belle II experiment and the final data set of 711 fb −1 recorded by the Belle experiment at the Υ(4S) resonance. The direct and mixing-induced time-dependent CP violation parameters C and S are determined along with two additional quantities, S + and S − , defined in the two halves of the $${m}^{2}\left({K}_{\text{S}}^{0}{\pi }^{+}\right)-{m}^{2}\left({K}_{\text{S}}^{0}{\pi }^{-}\right)$$ plane. The measured values are C = −0.17 ± 0.09 ± 0.04, S = −0.29 ± 0.11 ± 0.05, S + = −0.57 ± 0.23 ± 0.10 and S − = 0.31 ± 0.24 ± 0.05, where the first uncertainty is statistical and the second systematic.

We report the first search for the flavor-changing neutral-current decays B→X_{s}νν[over ¯], where X_{s} is a hadronic system with strangeness equal to 1, in data collected with the Belle II detector at the SuperKEKB asymmetric-energy e^{+}e^{-} collider. The data sample corresponds to an integrated luminosity of 365  fb^{-1} collected at the ϒ(4S) resonance and 43  fb^{-1} collected at a center-of-mass energy 60 MeV below resonance for estimation of e^{+}e^{-}→qq[over ¯] continuum background. One of the B mesons from the ϒ(4S)→BB[over ¯] decay is fully reconstructed in a hadronic decay mode. The B→X_{s}νν[over ¯] decay is reconstructed with a sum-of-exclusives approach that uses 30 X_{s} decay modes. This approach provides high sensitivity to the inclusive decay, despite the presence of two undetected neutrinos. The search is performed in three regions of the X_{s} mass, M_{X_{s}}^{true}, chosen to separate contributions from K, K^{*}(892), and heavier strange final states. We do not observe a significant signal and set upper limits at 90% confidence level on the partial branching fractions for the regions 0.0<M_{X_{s}}^{true}<0.6  GeV/c^{2}, 0.6<M_{X_{s}}^{true}<1.0  GeV/c^{2}, and 1.0  GeV/c^{2}<M_{X_{s}}^{true} of 2.2×10^{-5}, 9.3×10^{-5}, and 30.9×10^{-5}, respectively. Combining the three mass regions, we obtain the upper limit on the branching fraction, B(B→X_{s}νν[over ¯])<3.3×10^{-4}.

We report the first search for the flavor-changing neutral-current decays B -> X-s nu(nu) over bar, where X-s is a hadronic system with strangeness equal to 1, in data collected with the Belle II detector at the SuperKEKB asymmetric-energy e(+)e(-) collider. The data sample corresponds to an integrated luminosity of 365 fb(-1) collected at the Upsilon(4S) resonance and 43 fb(-1) collected at a center-of-mass energy 60 MeV below resonance for estimation of e(+)e(-) -> q (q) over bar continuum background. One of the B mesons from the Upsilon(4S) -> B (B) over bar decay is fully reconstructed in a hadronic decay mode. The B -> X-s nu(nu) over bar decay is reconstructed with a sum-of-exclusives approach that uses 30 X-s decay modes. This approach provides high sensitivity to the inclusive decay, despite the presence of two undetected neutrinos. The search is performed in three regions of the X-s mass, M-Xs(true), chosen to separate contributions from K, K+(892), and heavier strange final states. We do not observe a significant signal and set upper limits at 90% confidence level on the partial branching fractions for the regions 0.0 < M-Xs(true) < 0.6 GeV/c(2), 0.6 < M-Xs(true) < 1.0 GeV/c(2), and 1.0 GeV/c(2) < M-Xs(true) of 2.2 x 10(-5), 9.3 x 10(-5), and 30.9 x 10(-5), respectively. Combining the three mass regions, we obtain the upper limit on the branching fraction, B(B -> X-s nu(nu) over bar) < 3.3 x 10(-4).

We report the first searches for charged-lepton-flavor violation in decays of χ_{bJ}(1P) (J=0, 1, and 2) to a pair of charged leptons using 158 million ϒ(2S) decays collected with the Belle detector in e^{+}e^{-} collisions at the KEKB collider. No significant signal is observed, and we set upper limits on the branching fractions for χ_{bJ}(1P) decays to e^{±}μ^{∓} at the level of 10^{-6} and to e^{±}τ^{∓} or μ^{±}τ^{∓} at the level of 10^{-5}. Limits on χ_{b0}(1P) decays are translated into bounds on the corresponding Wilson coefficients of scalar operators that mediate charged-lepton-flavor violation.

We report decay-rate CP asymmetries of the singly-Cabibbo-suppressed decays Xi(+)(c) -> Sigma(+) h(+) h(-) and Lambda(+)(c) -> ph(+) h(-), with h = K, pi, measured using 428 fb(-1) of e(+)e(-) collisions collected by the Belle II experiment at the SuperKEKB collider. The results, A(CP) ( Xi(+)(c) -> Sigma(+) K+ K-) = (3.7 +/- 6.6 +/- 0.6)%, A(CP) ( Xi(+)(c) -> Sigma(+) pi(+) pi(-)) = (9.5 +/- 6.8 +/- 0.5)%, A(CP) (Lambda(+)(c) -> pK(+) K-) = (3.9 +/- 1.7 +/- 0.7)%, A(CP) (Lambda(+)(c) -> p pi(+) pi(-)) = (0.3 +/- 1.0 +/- 0.2)%, where the first uncertainties are statistical and the second systematic, agree with CP symmetry. From these results we derive the sums A(CP) ( Xi(+)(c) -> Sigma(+) pi(+) pi(-)) + A(CP) (Lambda(+)(c) -> pK(+) K-) = (13.4 +/- 7.0 +/- 0.9)%, A(CP) ( Xi(+)(c) -> Sigma(+) K+ K-) + A(CP) (Lambda(+)(c) -> p pi(+) pi(-)) = (4.0 +/- 6.6 +/- 0.7)%, which are consistent with the U-spin symmetry prediction of zero. These are the first measurements of CP asymmetries for individual hadronic three-body charmed-baryon decays.

We report a measurement of the branching fraction for the leptonic decay B^+^+ν_μ. This work presents the first B^+^+ν_μ result using Belle II data, an updated Belle measurement that supersedes the previous result, and their combination, which yields the most precise search to date. The analysis is based on 1076 fb^-1 of e^+e^- collision data collected at a center-of-mass energy of 10.58 GeV with the Belle and Belle II detectors at the KEKB and SuperKEKB colliders, respectively. We measure ℬ(B^+^+ν_μ)=(4.4±1.9± 1.0)×10^-7, where the first uncertainty is statistical and the second systematic. The observed significance relative to the background-only hypothesis is 2.4 standard deviations. We set a 90% confidence level upper limit of ℬ(B^+^+ν_μ)<6.7×10^-7 using a frequentist approach and a 90% credibility level upper limit of ℬ(B^+^+ν_μ)<7.2× 10^-7 using a Bayesian approach. These are the most stringent limits to date. The result is interpreted as an exclusion region in the parameter space of type II and type III two-Higgs-doublet models. We search for stable sterile neutrinos with masses m_N∈[0,1.5] GeV. No signal is observed, and the resulting exclusion on the squared mixing parameter |U_μN|^2 provides improvement over previous limits. We report a measurement of the partial branching fraction of semileptonic B→ X_u_ℓ decays with p_μ^B>2.2 GeV, obtaining Δℬ(B→ X_u_ℓ)=(2.72±0.05±0.29)×10^-4. We present a model-dependent study of weak annihilation decays using the muon momentum spectrum. We observe a signal of 2.4 standard deviations above the background-only hypothesis in regions where the distribution resembles that of B→ X_u_ℓ decays.

We report the first observation of the radiative decay D_{s0}^{*}(2317)^{+}→D_{s}^{*+}γ with a statistical significance exceeding 10 standard deviations. The signal is observed in the continuum e^{+}e^{-}→cc[over ¯] process, using combined data samples of 980.4  fb^{-1} from Belle and 427.9  fb^{-1} from Belle II, collected at the KEKB and SuperKEKB asymmetric-energy e^{+}e^{-} colliders, respectively. The branching fraction ratio B[D_{s0}^{*}(2317)^{+}→D_{s}^{*+}γ]/B[D_{s0}^{*}(2317)^{+}→D_{s}^{+}π^{0}] is measured to be [7.13±0.70(stat)±0.26(syst)]%. This result provides crucial discrimination between theoretical models of the D_{s0}^{*}(2317)^{+} structure.

Abstract 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 $$\sqrt{s}$$ 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 $$\sqrt{s}\sim 10.75$$ 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 b1 ω and Υ(10753) → χ b2 ω are (1.57 ± 0.27(stat.) ± 0.22(syst.)) eV and (1.39 ± 0.41(stat.) ± 0.33(syst.)) eV.

A sample of 365 fb(-1) of e(+)e(-) -> Y(4S) -> B (B) over bar data collected by the Belle II experiment is used to measure the partial branching fractions of charmless semileptonic B meson decays and determine the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element V-ub. Events containing a signal electron or muon l and a fully reconstructed hadronic B decay that constrains the signal kinematics are selected, while the rest of the event defines the hadronic system X-u associated with the signal. To discriminate the signal from the 50-times larger background originating from CKM-favored semileptonic B decays, a template fit is performed in both signal and control regions after applying an optimized selection. The partial branching fraction measured for lepton energies greater than 1 GeV in the signal B meson rest frame is Delta B(B -> X(u)l nu) = (1.54 +/- 0.08(stat) +/- 0.12(syst)) x 10(-3). From this measurement, using the Gambino, Giordano, Ossola, Uraltsev theoretical framework, vertical bar V-ub vertical bar = (4.01 +/- 0.19(-0.08)(+0.07)) x 10(-3) is determined, where the uncertainties are experimental and theoretical, respectively. This value is consistent with the world average obtained from previous inclusive measurements. Different theoretical predictions and partial branching fractions measured in other phase-space regions, defined by additional selections on the X-u and leptonic system masses, are also used to determine vertical bar V-ub vertical bar. This allows for a comparison of the resulting values across theoretical frameworks and phase-space regions.

We report the first searches for charged-lepton-flavor violation in decays of χ_bJ(1P) (J=0, 1, and 2) to a pair of charged leptons using 158 million Υ(2S) decays collected with the Belle detector in e^+e^- collisions at the KEKB collider. No significant signal is observed, and we set upper limits on the branching fractions for χ_bJ(1P) decays to e^^∓ at the level of 10^-6 and to e^^∓ or μ^^∓ at the level of 10^-5. Limits on χ_b0(1P) decays are translated into bounds on the corresponding Wilson coefficients of scalar operators that mediate charged-lepton-flavor violation.

We present a measurement of the time-dependent CP asymmetry in B-0 -> K-S(0)pi(+)pi(-)(gamma) decays using a data set of 365 fb(-1) recorded by the Belle II experiment and the final data set of 711 fb(-1) recorded by the Belle experiment at the Upsilon(4S) resonance. The direct and mixing-induced time-dependent CP violation parameters C and S are determined along with two additional quantities, S+ and S-, defined in the two halves of the m(2)(K-S(0)pi(+)) - m2(K-S(0)pi(-)) plane. The measured values are C = -0.17 +/- 0.09 +/- 0.04, S = -0.29 +/- 0.11 +/- 0.05, S+ = -0.57 +/- 0.23 +/- 0.10 and S- = 0.31 +/- 0.24 +/- 0.05, where the first uncertainty is statistical and the second systematic.

Using data samples of 988.4 fb(-1) and 427.9 fb(-1) collected with the Belle and Belle II detectors, we present a study of the singly Cabibbo-suppressed decays Xi(0)(c) -> Lambda eta, Lambda eta ', and Lambda pi(0). We observe the decay Xi(0)(c) -> Lambda eta and find evidence for the decay Xi(0)(c)->Lambda eta ', with corresponding branching ratios determined to be B(Xi(0)(c) -> Lambda eta)/B(Xi(0)(c) -> Xi(-)pi(+)) = (4.16 +/- 0.91 +/- 0.23)% and B( Xi(0)(c) -> Lambda eta ')/B(Xi(0)(c) -> Xi(-)pi(+)) = (2.48 +/- 0.82 +/- 0.12)%, respectively. We find no significant signal in the Xi(0)(c) -> Lambda pi(0) decay mode and set an upper limit at the 90% credibility level of B(Xi(0)(c) -> Xi(-)pi(+))/B(Xi(0)(c) -> Xi(-)pi(+)) < 3.5%. Multiplying these ratios by the world-average branching fraction of the normalization channel, B(Xi(0)(c) -> Xi(-)pi(+)) = (1.43 +/- 0.27)%, we obtain the absolute branching fractions of B(Xi(0)(c) -> Lambda eta) = (5.95 +/- 1.30 +/- 0.32 +/- 1.13) x 10(-4), B(Xi(0)(c) -> Lambda eta ') (3.55 +/- 1.17 +/- 0.68) x 10(-4), and an upper limit at the 90% credibility level on the absolute branching fraction of B(Xi(0)(c) -> Lambda pi(0)) < 5.2 x 10(-4). The quoted first and second uncertainties are statistical and systematic, respectively, while the third uncertainties arise from the branching fraction of the normalization mode. These results are consistent with most theoretical predictions and further the understanding of the underlying decay mechanisms.

We study the processes χbJ ω and χbJ (π+π−π0)non−ω (J = 0, 1, 2) at center-of-mass energies √(s) 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 √(s)∼ 10.75 GeV using a 19.8 fb−1 sample collected with Belle II at SuperKEKB. We find that the Υ(10753) state decays into χbJ ω but not into χbJ (π+π−π0)non−ω, while the Υ(10860) state, in contrast, decays into χbJ (π+π−π0)non−ω but not into χbJ ω. The mass and width of the Υ(10753) state are measured to be (10756.1 ± 3.4(stat.) ± 2.7(syst.)) MeV/c2 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) → χb1 ω and Υ(10753) → χb2 ω are (1.57 ± 0.27(stat.) ± 0.22(syst.)) eV and (1.39 ± 0.41(stat.) ± 0.33(syst.)) eV.

We search for the e(+)e(-) -> gamma chi(bJ) (J = 0, 1, 2) processes at center-of-mass energies root s = 10.653, 10.701, 10.746, and 10.804 GeV. These data were collected with the Belle II detector at the SuperKEKB collider and correspond to 3.5, 1.6, 9.8, and 4.7 fb(-1) of integrated luminosity, respectively. We set upper limits at the 90% confidence level on the Born cross sections for e(+)e(-) -> gamma chi(bJ) at each center-of-mass energy root s near 10.746 GeV. The upper limits at 90% confidence level on the Born cross sections for e(+)e(-) -> gamma chi(b1) are significantly smaller than the corresponding measured values fore e(+)e(-) -> omega chi(b1) and e(+)e(-) -> pi(+)pi(-) Upsilon(2S) at root s = 10.746 GeV.

Using data samples collected by the Belle and Belle II experiments at the Υ(4S) resonance with integrated luminosities of 571 fb−1 and 365 fb−1, respectively, we measure the pseudoscalar B-meson mass difference to be m(B0) − m(B+) = (0.495 ± 0.024 ± 0.005) MeV/c2. The results are based on a simultaneous fit to the variable M_bc , which is related to the B momentum, for B0 and B+ candidates; and to the energy dependence of ℛ=σ (e^+e^-→B^0B^0) / σ (e^+e^-→B^+B^-) , which is measured using changes in the average center-of-mass energy over the data taking periods. The phase-space hypothesis ℛ=(p_B^0 /p_B^+)^3 , upon which previous measurements rely, is strongly disfavored by our fit; the measured mass-difference value for the phase-space hypothesis also differs significantly from our measurement. We constrain ℛ in a broader energy range than covered by the direct measurement and extract the energy dependence of ℛ in the range from the BB threshold up to 10.59 GeV. We interpret the results using a phenomenological model and constrain the parameters of the BB potential in the isovector channel.

Using a data sample of 427.9 fb^-1 collected by the Belle II detector at or near the Υ(4S) and Υ(10753) resonances, the cross sections for e^+e^-→ h^+h^-J/ψ (h=π/K/p) at center-of-mass energies ranging from 3.8 GeV or the production threshold to 5.5/6.0/7.0 GeV have been measured via initial-state radiation. The cross sections for the processes e^+e^-→ π^+π^-J/ψ and e^+e^-→ K^+K^-J/ψ are consistent with previously published results. The cross sections for these channels obtained by combining with previous Belle results are also given. The process e^+e^-→ pp̅ J/ψ is investigated for the first time. The yields are small and no significant structure is observed in the cross section versus energy. Searches for vector charmonium-like states in the h^+h^-J/ψ systems, and for associated intermediate states in the h^± J/ψ systems, are also presented.

Abstract Using data samples collected by the Belle and Belle II experiments at the Υ(4S) resonance with integrated luminosities of 571 fb −1 and 365 fb −1, respectively, we measure the pseudoscalar B-meson mass difference to be m(B 0) − m(B +) = (0.495 ± 0.024 ± 0.005) MeV/c 2. The results are based on a simultaneous fit to the variable $${\overline{M} }_{bc}$$ , which is related to the B momentum, for B 0 and B + candidates; and to the energy dependence of $$\mathcal{R}=\sigma ({e}^{+}{e}^{-}\to {B}^{0}{\overline{B} }^{0}) / \sigma ({e}^{+}{e}^{-}\to {B}^{+}{B}^{-})$$ , which is measured using changes in the average center-of-mass energy over the data taking periods. The phase-space hypothesis $$\mathcal{R}={({p}_{{B}^{0}} /{p}_{{B}^{+}})}^{3}$$ , upon which previous measurements rely, is strongly disfavored by our fit; the measured mass-difference value for the phase-space hypothesis also differs significantly from our measurement. We constrain $$\mathcal{R}$$ in a broader energy range than covered by the direct measurement and extract the energy dependence of $$\mathcal{R}$$ in the range from the $$B\overline{B }$$ threshold up to 10.59 GeV. We interpret the results using a phenomenological model and constrain the parameters of the $$B\overline{B }$$ potential in the isovector channel.

We report the first search for the flavor-changing neutral-current decays B → X s ν ν ¯ , where X s is a hadronic system with strangeness equal to 1, in data collected with the Belle II detector at the SuperKEKB asymmetric-energy e + e − collider. The data sample corresponds to an integrated luminosity of 365 fb − 1 collected at the ϒ ( 4 S ) resonance and 43 fb − 1 collected at a center-of-mass energy 60 MeV below resonance for estimation of e + e − → q q ¯ continuum background. One of the B mesons from the ϒ ( 4 S ) → B B ¯ decay is fully reconstructed in a hadronic decay mode. The B → X s ν ν ¯ decay is reconstructed with a sum-of-exclusives approach that uses 30 X s decay modes. This approach provides high sensitivity to the inclusive decay, despite the presence of two undetected neutrinos. The search is performed in three regions of the X s mass, M X s true , chosen to separate contributions from K , K * ( 892 ) , and heavier strange final states. We do not observe a significant signal and set upper limits at 90% confidence level on the partial branching fractions for the regions 0.0 < M X s true < 0.6 GeV / c 2 , 0.6 < M X s true < 1.0 GeV / c 2 , and 1.0 GeV / c 2 < M X s true of 2.2 × 10 − 5 , 9.3 × 10 − 5 , and 30.9 × 10 − 5 , respectively. Combining the three mass regions, we obtain the upper limit on the branching fraction, B ( B → X s ν ν ¯ ) < 3.3 × 10 − 4 .

We present a search for an invisible hidden-sector particle X_{inv}, produced in B^{0}→D[over ¯]^{0}X_{inv} and B^{±}→hX_{inv} decays, where h=π^{±}, K^{±}, D_{s}^{±}, p^{±}. The search is performed using e^{+}e^{-} collision data recorded with the Belle detector, corresponding to 711  fb^{-1}. No significant signal is observed. We set 90% confidence level upper limits ranging between 10^{-4} and 10^{-6} on the branching fraction B(B→hX_{inv}) as a function of m_{X_{inv}}. Corresponding limits are set on B(B→hX)×B(X→γγ) for lifetimes cτ_{X} between 10  μm and 10 m. Many of these limits are the first direct constraints on their respective decays. Our results provide the most stringent exclusion limits to date on the branching fractions for all search channels, and exclude previously unexplored regions of parameter space relevant to several new physics models.