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^+→ pK_S^0 , Ξ_c^+→Λπ^+ , and Ξ_c^+→Σ^0π^+ are observed for the first time. The ratios of branching fractions of Ξ_c^+→ pK_S^0 , Ξ_c^+→Λπ^+ , and Ξ_c^+→Σ^0π^+ relative to that of Ξ_c^+→Ξ^-π^+π^+ are measured to be [ ℬ(Ξ_c^+→ pK_S^0)/ℬ(Ξ_c^+→Ξ^-π^+π^+)=(2.47± 0.16± 0.07)%,; ℬ(Ξ_c^+→Λπ^+)/ℬ(Ξ_c^+→Ξ^-π^+π^+)=(1.56± 0.14± 0.09)%,; ℬ(Ξ_c^+→Σ^0π^+)/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^+→ pK_S^0)=(7.16± 0.46± 0.20± 3.21)×10^-4,; ℬ(Ξ_c^+→Λπ^+)=(4.52± 0.41± 0.26± 2.03)×10^-4,; ℬ(Ξ_c^+→Σ^0π^+)=(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^+) .

Using the data samples of 102 million $\Upsilon(1S)$ and 158 million $\Upsilon(2S)$ events collected by the Belle detector, we search for a pentaquark state in the $pJ/\psi$ final state from $\Upsilon(1,2S)$ inclusive decays. Here, the charge-conjugate $\bar{p}J/\psi$ is included. We observe clear $pJ/\psi$ production in $\Upsilon(1,2S)$ decays and measure the branching fractions to be $\mathcal{B}[\Upsilon(1S) \to pJ/\psi + anything] = [4.27 \pm 0.16(stat.) \pm 0.20(syst.)] \times 10^{-5}$ and $\mathcal{B}[\Upsilon(2S) \to pJ/\psi + anything] = [3.59 \pm 0.14(stat.) \pm 0.16(syst.)] \times 10^{-5}$. We also measure the cross section of inclusive $pJ/\psi$ production in $e^+e^-$ annihilation to be $\sigma(e^+e^- \to pJ/\psi + anything) = [57.5 \pm 2.1 (stat.) \pm 2.5(syst.)]$~fb at $\sqrt{s} = 10.52~\hbox{GeV}$ using an 89.5~fb$^{-1}$ continuum data sample. There is no significant $P_c(4312)^+$, $P_c(4440)^+$ or $P_c(4457)^+$ signal found in the $pJ/\psi$ final states in $\Upsilon(1,2S)$ inclusive decays. We determine the upper limits of $\mathcal{B}[\Upsilon(1,2S)\to P_c^{+} + anything] \cdot \mathcal{B}(P_c^{+}\to pJ/\psi)$ to be at the $10^{-6}$ level.

We measure the time-integrated CP asymmetry in D-0 -> (KSKS0)-K-0 decays reconstructed in e(+)e(-) -> c (c) over bar events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 and 428 fb(-1), respectively. The D-0 decays are required to originate from the D*(+) -> D-0 pi(+) decay, which determines the charm flavor at production time. A control sample of D-0 -> K+K- decays is used to correct for production and detection asymmetries. The result, (-1.4 +/- 1.3(stat) +/- 0.1(syst))%, is consistent with previous determinations and with CP symmetry.

Spin-1/2 inelastic dark matter (DM) models are popular among sub-GeV to GeV thermal DM scenarios due to the dominant role of co-annihilation in determining the DM relic abundance. In these models, the dark Higgs boson plays a crucial role in generating the mass of the new gauge boson, the dark photon (A′), and in establishing the mass splitting between the excited (χ2) and ground (χ1) states of DM. In particular, the Compton scattering χ1A′ → χ_2^∗ → χ1A′ and its t-channel crossed process, χ1χ1 → A′A′, remain unitary for high energy longitudunal dark photon, only if the contribution of the dark Higgs boson is included. However, experimental searches for the dark Higgs boson have received relatively little attention. In particular, when the dark Higgs boson mass exceeds twice that of the DM excited state, its decay signatures become semi-visible or invisible, making detection challenging with current light scalar search strategies. In this work, we explore the prospects for detecting the elusive dark Higgs boson in spin-1/2 inelastic DM models at Belle II via dark Higgs-strahlung and rare B meson decay processes. Our analysis indicates that both the inclusive signature of two displaced dilepton vertices and the additional missing energy from dark Higgs boson decays serve as robust indicators of its presence. Furthermore, we assess the future potential for detecting the dark Higgs boson with the proposed far detector related to Belle II, GAZELLE.

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) × 106 Υ(4S) events. We measure branching fractions ( ℬ ) and CP asymmetries ( 𝒜_CP ) for both B0 → K*0γ and B+ → K*+γ decays. The difference in CP asymmetries ( Δ𝒜_CP ) and the isospin asymmetry (∆0+) between these neutral and charged channels are also measured. We obtain the following branching fractions and CP asymmetries: ℬ(B^0→K^*0γ)=(4.14± 0.10± 0.11)×10^-5 , ℬ(B^+→K^*+γ)=(4.04±0.13_-0.15^+0.13)×10^-5 , 𝒜_CP(B^0→K^*0γ)=(-3.3± 2.3± 0.4)% , and Δ𝒜_CP(B^+→K^*+γ)=(-0.7± 2.9± 0.5)% . The measured difference in CP asymmetries is Δ𝒜_CP=(+2.6±3.8± 0.6)% , and the measured isospin asymmetry is ∆0+ = (+4.8 ± 2.0 ± 1.8)

We perform the first search for CP violation in D_(s)^+→K_S^0K^-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(4S) 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 D^+→K_S^0K^-π^+π^+ decays, and better than 0.3 D_s^+→K_S^0K^-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.

We present measurements of B+ -> rho(+) gamma and B-0 -> rho(0) gamma. decays using a combined data sample of 772 x 10(6) B (B) over bar pairs collected by the Belle experiment and 387 x 10(6) B (B) over bar pairs collected by the Belle II experiment in e(+) e(-) collisions at the Upsilon(4S) resonance. After an optimized selection, a simultaneous fit to the Belle and Belle II datasets yields 114 +/- 12 B+ -> rho(+) gamma. and 99 +/- 12 B-0 -> rho(0) gamma decays. The measured branching fractions are (13.1(-1.9-1.2)(+2.0+1.3)) x 10(-7) and (7.6 +/- 1.3(-0.8)(+1.0)) x 10(-7) for B+ -> rho(+) gamma. and B-0 -> rho(0) gamma. decays, respectively, where the first uncertainty is statistical and the second is systematic. We also measure the isospin asymmetry A(I)(B -> rho gamma) = (10.9(-11.7-7.3)(+11.2+7.8))% and the direct CP asymmetry A(CP)(B+ -> rho(+) gamma) = (-8.2 +/- 15.2(-1.3)(+2.0))%.

We present a measurement of the ratio of partial branching fractions of the semileptonic inclusive decays, B-* Xul nu to B-* Xcl nu, where l 1/4 (e; mu), using the full Belle sample of 772 x 106 BB pairs collected at the Y(4S) resonance. The identification of inclusive B-* Xul nu decays is difficult due to the abundance of Cabibbo-Kobayashi-Maskawa-favored B-* Xcl nu events, which share a similar event topology. To minimize dependence on the modeling of these channels, a data-driven description of B-* Xcl nu is employed. The ratio is measured via a two-dimensional fit to the squared four-momentum transfer to the lepton pair, and the charged lepton energy in the B meson rest frame, where the latter must be larger than 1 GeV, covering approximately 86% and 78% of the B-* Xul nu and B-* Xcl nu phase space, respectively. We find oB(B-* Xul nu)/oB(B-* Xcl nu) 1/4 (1.99 +/- 0.17stat +/- 0.16syst) x 10-2, where the uncertainties are statistical and systematic, respectively. We extract jVubj/jVcbj using two theoretical calculations for the partial decay rate of B-* Xul nu, finding (jVubj/jVcbj)BLNP 1/4 (9.81 +/- 0.42stat +/- 0.38syst +/- 0.51or(B-*Xul nu) +/- 0.20or(B-*Xcl nu)) x 10-2 and (jVubj/jVcbj)GGOU 1/4 (10.06 +/- 0.43stat +/- 0.39syst +/- 0.23or(B-*Xul nu) +/- 0.20or(B-*Xcl nu)) x 10-2, where the third and fourth uncertainties are from the partial decay rates of B-* Xul nu and B-* Xcl nu, respectively. In addition, we report the partial branching fractions separately for charged and neutral B meson decays, and for electron and muon decay channels. We place a limit on isospin breaking in B-* Xul nu decays, and find no indication of lepton flavor universality violation in either the charmed or charmless mode. Furthermore, we unfold the B-* Xul nu and B-* Xcl nu yields and report the differential ratio in lepton energy and four-momentum transfer squared.

Abstract We report measurements of the absolute branching fractions $$\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)$$ , $$\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)$$ , and $$\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right)$$ , where the latter is measured for the first time. The results are based on a 121.4 fb −1 data sample collected at the Υ(10860) resonance by the Belle detector at the KEKB asymmetric-energy e + e − collider. We reconstruct one $${B}_{s}^{0}$$ meson in $${e}^{+}{e}^{-}\to \Upsilon\left(10860\right)\to {B}_{s}^{*}{\overline{B} }_{s}^{*}$$ events and measure yields of $${D}_{s}^{+}$$ , D 0, and D + mesons in the rest of the event. We obtain $$\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(68.6\pm 7.2\pm 4.0\right)\%$$ , $$\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(21.5\pm 6.1\pm 1.8\right)\%$$ , and $$\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right)=\left(12.6\pm 4.6\pm 1.3\right)\%$$ , where the first uncertainty is statistical and the second is systematic. Averaging with previous Belle measurements gives $$\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(63.4\pm 4.5\pm 2.2\right)\%$$ and $$\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(23.9\pm 4.1\pm 1.8\right)\%$$ . For the $${B}_{s}^{0}$$ production fraction at the Υ(10860), we find $${f}_{s}=\left({21.4}_{-1.7}^{+1.5}\right)\%$$ .

We present a measurement of the branching fraction and time-dependent charge-parity (CP) decay-rate asymmetries in B0→J/ψπ0 decays. The data sample was collected with the Belle II detector at the SuperKEKB asymmetric e+e− collider in 2019–2022 and contains (387±6)×106 BB¯ meson pairs from ϒ(4S) decays. We reconstruct 392±24 signal decays and fit the CP parameters from the distribution of the proper-decay-time difference of the two B mesons. We measure the branching fraction to be (B0→J/ψπ0)=(2.00±0.12±0.09)×10−5 and the direct and mixing-induced CP asymmetries to be CCP=0.13±0.12±0.03 and SCP=−0.88±0.17±0.03, respectively, where the first uncertainties are statistical and the second are systematic. We observe mixing-induced CP violation with a significance of 5.0 standard deviations for the first time in this mode. Published by the American Physical Society 2025

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 (e(+) e(-) -> e(+) e(-)(n gamma)), digamma (e(+) e(-) -> gamma gamma(n gamma)), and dimuon (e(+) e(-) -> mu(+) mu(-)(n gamma)) 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).

We report measurements of time-dependent CP asymmetries in B^{0}→K_{S}^{0}π^{0}γ decays based on a data sample of (388±6)×10^{6}  BB[over ¯] events collected at the ϒ(4S) resonance with the Belle II detector. The Belle II experiment operates at the SuperKEKB asymmetric-energy e^{+}e^{-} collider. We measure decay-time distributions to determine CP -violating parameters S and C. We determine these parameters for two ranges of K_{S}^{0}π^{0} invariant mass: m(K_{S}^{0}π^{0})∈(0.8,1.0)  GeV/c^{2}, which is dominated by B^{0}→K^{*0}(→K_{S}^{0}π^{0})γ decays, and a complementary region m(K_{S}^{0}π^{0})∈(0.6,0.8)∪(1.0,1.8)  GeV/c^{2}. Our results have improved precision as compared to previous measurements and are consistent with theory predictions.

We report on a search for a resonance X decaying to a pair of muons in e+e−→μ+μ−X events in the 0.212–9.000 GeV/c2 mass range, using 178 fb−1 of data collected by the Belle II experiment at the SuperKEKB collider at a center of mass energy of 10.58 GeV. The analysis probes two different models of X beyond the standard model: a Z′ vector boson in the Lμ−Lτ model and a muonphilic scalar. We observe no evidence for a signal and set exclusion limits at the 90% confidence level on the products of cross section and branching fraction for these processes, ranging from 0.046 fb to 0.97 fb for the Lμ−Lτ model and from 0.055 fb to 1.3 fb for the muonphilic scalar model. For masses below 6 GeV/c2, the corresponding constraints on the couplings of these processes to the standard model range from 0.0008 to 0.039 for the Lμ−Lτ model and from 0.0018 to 0.040 for the muonphilic scalar model. These are the first constraints on the muonphilic scalar from a dedicated search. Published by the American Physical Society 2024

We search for the rare decay B+ -> K+ v (v) over bar in a 362 fb(-1) sample of electron-positron collisions at the Upsilon(4S) resonance collected with the Belle II detector at the SuperKEKB collider. We use the inclusive properties of the accompanying B meson in Upsilon(4S) -> B (B) over bar events to suppress background from other decays of the signal B candidate and light-quark pair production. We validate the measurement with an auxiliary analysis based on a conventional hadronic reconstruction of the accompanying B meson. For background suppression, we exploit distinct signal features using machine learning methods tuned with simulated data. The signal-reconstruction efficiency and background suppression are validated through various control channels. The branching fraction is extracted in a maximum likelihood fit. Our inclusive and hadronic analyses yield consistent results for the B+ -> K+ v (v) over bar branching fraction of [2.7 +/- 0.5(stat) +/- 0.5(syst)] x 10(-5) and [1.1(-0.8)(+0.9)(stat)(-0.5)(+0.8)(syst)] x 10(-5), respectively. Combining the results, we determine the branching fraction of the decay B+ -> K+ v (v) over bar to be [2.3 +/- 0.5_stat)(-0.4)(+0.5)(syst)] x 10(-5), providing the first evidence for this decay at 3.5 standard deviations. The combined result is 2.7 standard deviations above the standard model expectation.

We present measurements of the branching fractions of eight B^0→ D^(*)+ K^- K^(*)0_(S), B^-→ D^(*)0 K^- K^(*)0_(S) decay channels. The results are based on data from SuperKEKB electron-positron collisions at the Υ(4S) resonance collected with the Belle II detector, corresponding to an integrated luminosity of 362 fb^-1. The event yields are extracted from fits to the distributions of the difference between expected and observed B meson energy, and are efficiency-corrected as a function of m(K^-K^(*)0_(S)) and m(D^(*)K^(*)0_(S)) in order to avoid dependence on the decay model. These results include the first observation of B^0→ D^+K^-K_S^0, B^-→ D^*0K^-K_S^0, and B^0→ D^*+K^-K_S^0 decays and a significant improvement in the precision of the other channels compared to previous measurements. The helicity-angle distributions and the invariant mass distributions of the K^- K^(*)0_(S) systems are compatible with quasi-two-body decays via a resonant transition with spin-parity J^P=1^- for the K^-K_S^0 systems and J^P= 1^+ for the K^-K^*0 systems. We also present measurements of the branching fractions of four B^0→ D^(*)+ D_s^-, B^-→ D^(*)0 D_s^- decay channels with a precision compatible to the current world averages.

We search for the e(+) e(-) -> eta(b)(1S)omega and e(+) e(-) -> chi(b0)(1P)omega processes at a center-of-mass energy of 10.745 GeV, which is close to the peak of the Upsilon(10753) state. We use data collected by the Belle II experiment during a special run, corresponding to an integrated luminosity of 9.8 fb(-1). We reconstruct omega -> pi(+) pi(-) pi(0) decays and use the. meson's recoil mass to search for the signals. We do not find evidence for either process, and set upper limits on the corresponding Born-level cross sections of 2.5 pb and 7.8 pb, respectively, at the 90% confidence level. The chi(b0)(1P)omega limit is the result of a combination of this analysis and a previous search using full reconstruction.

We measure the tau-to-light-lepton ratio of inclusive B-meson branching fractions R ( X tau= l ) equivalent to B ( B-* X tau nu ) = B ( B-* X l nu ) , where l indicates an electron or muon, and thereby test the universality of charged-current weak interactions. We select events that have one fully reconstructed B meson and a charged lepton candidate from 189 fb-1 - 1 of electron-positron collision data collected with the Belle II detector. We find R ( X tau= l ) = 0.228 + 0.016(stat) ( stat ) + 0.036(syst), ( syst ) , in agreement with standard-model expectations. This is the first direct measurement of R ( X tau= l ) .

Abstract 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 $$ {K}_S^0{\pi}^0 $$ K S 0 π 0 , where D is an admixture of D0 and $$ {\overline{D}}^0 $$ D ¯ 0 states. These decays are sensitive to the Cabibbo-Kobayashi-Maskawa unitarity-triangle angle ϕ3. The results are based on a combined analysis of the final data set of 772 × 106$$ B\overline{B} $$ B B ¯ pairs collected by the Belle experiment and a data set of 198 × 106$$ B\overline{B} $$ B B ¯ pairs collected by the Belle II experiment, both in electron-positron collisions at the Υ(4S) resonance. We measure the CP asymmetries to be $$ \mathcal{A} $$ A CP+ = (+12.5 ± 5.8 ± 1.4)% and $$ \mathcal{A} $$ A CP− = (−16.7 ± 5.7 ± 0.6)%, and the ratios of branching fractions to be $$ \mathcal{R} $$ R CP+ = 1.164 ± 0.081 ± 0.036 and $$ \mathcal{R} $$ R CP− = 1.151 ± 0.074 ± 0.019. The first contribution to the uncertainties is statistical, and the second is systematic. The asymmetries $$ \mathcal{A} $$ A CP+ and $$ \mathcal{A} $$ 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° < ϕ3 < 16.5°) or (84.5° < ϕ3 < 95.5°) or (163.3° < ϕ3 < 171.5°) and 0.321 < rB < 0.465.

We report an estimation of the injected mass composition of ultrahigh energy cosmic rays (UHECRs) at energies higher than 10 EeV. The composition is inferred from an energy-dependent sky distribution of UHECR events observed by the Telescope Array surface detector by comparing it to the Large Scale Structure of the local Universe. In the case of negligible extragalactic magnetic fields (EGMFs), the results are consistent with a relatively heavy injected composition at E similar to 10 EeV that becomes lighter up to E similar to 100 EeV, while the composition at E > 100 EeV is very heavy. The latter is true even in the presence of highest experimentally allowed extragalactic magnetic fields, while the composition at lower energies can be light if a strong EGMF is present. The effect of the uncertainty in the galactic magnetic field on these results is subdominant.

We report the first evidence for the h_b(2P) →Υ(1S)η transition with a significance of 3.5 standard deviations. The decay branching fraction is measured to be ℬ[h_b(2P) →Υ(1S)η]=(7.1  ^+3.7 _-3.2± 0.8)×10^-3, which is noticeably smaller than expected. We also set upper limits on π^0 transitions of ℬ[h_b(2P) →Υ(1S)π^0] < 1.8×10^-3, and ℬ[h_b(1P)→Υ(1S)π^0] < 1.8×10^-3, at the 90% confidence level. These results are obtained with a 131.4 fb^-1 data sample collected near the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e^+e^- collider.