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.

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 983.0 fb−1 and 427.9 fb−1 data samples collected with the Belle and Belle II detectors at the KEKB and SuperKEKB asymmetric energy e+e− colliders, respectively, we present studies of the Cabibbo-favored Ξ_c^+ decays Ξ_c^+→Σ^+K_S^0 and Ξ_c^+→Ξ^0π^+ , and the singly Cabibbo-suppressed decay Ξ_c^+→Ξ^0K^+ . The ratios of branching fractions of Ξ_c^+→Σ^+K_S^0 and Ξ_c^+→Ξ^0K^+ relative to that of Ξ_c^+→Ξ^-π^+π^+ are measured for the first time, while the ratio ℬ(Ξ_c^+→Ξ^0π^+)/ℬ(Ξ_c^+→Ξ^-π^+π^+) is also determined and improved by an order of magnitude in precision. The measured branching fraction ratios are [ ℬ(Ξ_c^+→Σ^+K_S^0)/ℬ(Ξ_c^+→Ξ^-π^+π^+)=0.067± 0.007± 0.003,; ℬ(Ξ_c^+→Ξ^0π^+)/ℬ(Ξ_c^+→Ξ^-π^+π^+)=0.251± 0.005± 0.010,; ℬ(Ξ_c^+→Ξ^0K^+)/ℬ(Ξ_c^+→Ξ^-π^+π^+)=0.017± 0.003± 0.001. ] Additionally, the ratio ℬ(Ξ_c^+→Ξ^0K^+)/ℬ(Ξ_c^+→Ξ^0π^+) is measured to be 0.068 ± 0.010 ± 0.004. Here, the first and second uncertainties are statistical and systematic, respectively. Multiplying the ratios by the branching fraction of the normalization mode, ℬ(Ξ_c^+→Ξ^-π^+π^+)=(2.9± 1.3)% , we obtain the following absolute branching fractions [ ℬ(Ξ_c^+→Σ^+K_S^0)=(0.194± 0.021± 0.009± 0.087)%,; ℬ(Ξ_c^+→Ξ^0π^+)=(0.728± 0.014± 0.027± 0.326)%,; ℬ(Ξ_c^+→Ξ^0K^+)=(0.049± 0.007± 0.003± 0.022)%, ] where the third uncertainties are from ℬ(Ξ_c^+→Ξ^-π^+π^+) .

The CP-even fractions (F+) of the decays D0→π+π−π0 and D0→K+K−π0 are measured with a quantum-correlated ψ(3770)→DD¯ data sample collected by the BESIII experiment corresponding to an integrated luminosity of 7.93 fb−1. The results are F+π+π−π0=0.9406±0.0055±0.0033 and F+K+K−π0=0.631±0.014±0.011, where the first uncertainties are statistical and the second systematic. These measurements are consistent with the previous determinations, and the uncertainties for F+π+π−π0 and F+K+K−π0 are reduced by factors of 2.6 and 2.6, respectively. The reported results provide important inputs for the precise measurement of the angle γ of the Cabibbo-Kobayashi-Maskawa matrix and indirect CP violation in charm mixing. Published by the American Physical Society 2025

We present the results of a search for the charged-lepton-flavor violating decays B0 → K*0τ±ℓ∓, where ℓ∓ is either an electron or a muon. The results are based on 365 fb−1 and 711 fb−1 datasets collected with the Belle II and Belle detectors, respectively. We use an exclusive hadronic B-tagging technique, and search for a signal decay in the system recoiling against a fully reconstructed B meson. We find no evidence for B0 → K*0τ±ℓ∓ decays and set upper limits on the branching fractions in the range of (2.9–6.4)×10−5 at 90

Using psi(3686) -> pi(0)h(c) decays from a data sample of (27.12 +/- 0.14) x 10(8) psi(3686) events collected by the BESIII detector at the BEPCII collider, h(c) radiative decays to multiple light hadrons below 2.8 GeV/c(2)-gamma pi(+)pi(-), gamma pi(+)pi(-)eta, gamma 2(pi(+)pi(-)) and gamma p (p) over bar -are observed for the first time, each with a significance greater than 5 sigma. The corresponding branching fractions are measured. Furthermore, intermediate states are investigated, leading to the first observation of the decay process of h(c) -> gamma f(2)(1270) -> gamma pi(+)pi(-) with a significance of 5.1 sigma. This observation represents the first instance of h(c) radiative decay to a tensor state.

Abstract We report an improved study of the semileptonic decay D 0 → K ¯ 0 π − e + ν e $$ {D}^0\to {\overline{K}}^0{\pi}^{-}{e}^{+}{\nu}_e $$ based on a sample of 7.9 fb −1 of e + e − annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider. The branching fraction of this decay is measured to be B D 0 → K ¯ 0 π − e + ν e $$ \mathcal{B}\left({D}^0\to {\overline{K}}^0{\pi}^{-}{e}^{+}{\nu}_e\right) $$ = (1.444 ± 0.022stat ± 0.024syst)%, which is the most precise to date, where the first uncertainty is statistical and the second is systematic. Based on investigation of the decay dynamics, we find that the decay is dominated by the K *(892) − component and present an improved measurement of its branching fraction to be B D 0 → K ∗ 892 − e + ν e $$ \mathcal{B}\left({D}^0\to {K}^{\ast }{(892)}^{-}{e}^{+}{\nu}_e\right) $$ = (2.039 ± 0.032stat ± 0.034syst)%. We also determine the ratios of the hadronic form factors for the K *(892) − e + ν e decay to be r V = V(0)/A 1(0) = 1.48 ± 0.05stat ± 0.02syst and r 2 = A 2(0)/A 1(0) = 0.70 ± 0.04stat ± 0.02syst, where V(0) is the vector form factor and A 1,2(0) are the axial form factors. In addition, the K ¯ 0 π − $$ {\overline{K}}^0{\pi}^{-} $$ S $$ \mathcal{S} $$ -wave component is found to account for (5.87 ± 0.32stat ± 0.16syst)% of the total decay rate, corresponding to a branching fraction of B D 0 → K ¯ 0 π − S − wave e + ν e $$ B\left[{D}^0\to {\left({\overline{K}}^0{\pi}^{-}\right)}_{S-\textrm{wave}}{e}^{+}{\nu}_e\right] $$ = (0.085 ± 0.005stat ± 0.003syst)%.

Using a dataset of (27.12±0.14)×108 ψ(3686) events collected by the BESIII detector operating at the BEPCII collider, we report the first observation of the decay ψ(3686)→Σ0Σ¯0ω with a statistical significance of 8.9σ. The measured branching fraction is (1.24±0.16stat±0.11sys)×10−5, where the first uncertainty is statistical and the second is systematic. Additionally, we investigate potential intermediate states in the invariant mass distributions of Σ0ω, Σ¯0ω and Σ0Σ¯0. A hint of a resonance is observed in the invariant mass distribution of MΣ0(Σ¯0)ω, located around 2.06 GeV/c2, with a significance of 2.5σ. Published by the American Physical Society 2025

Abstract Using (2712 ± 14) × 106 ψ(3686) events collected with the BESIII detector, we perform the first amplitude analysis of the radiative decay ψ 3686 → γ K S 0 K S 0 $$ \psi (3686)\to \gamma {K}_S^0{K}_S^0 $$ within the mass region M K S 0 K S 0 < 2.8 $$ {M}_{K_S^0{K}_S^0}<2.8 $$ GeV/c 2. Employing a one-channel K-matrix approach for the description of the dynamics of the K S 0 K S 0 $$ {K}_S^0{K}_S^0 $$ system, the data sample is well described with four poles for the f 0-wave and three poles for the f 2-wave. The determined pole positions are consistent with those of well-established resonance states. The observed f 0 and f 2 states are found to be in agreement with those produced in radiative J/ψ decays. The production behaviors of f 0 and f 2 poles in ψ 3686 → γ K S 0 K S 0 $$ \psi (3686)\to \gamma {K}_S^0{K}_S^0 $$ are qualified with their residues and the converted branching fractions. By comparing with J / ψ → γ K S 0 K S 0 $$ J/\psi \to \gamma {K}_S^0{K}_S^0 $$ decay, the ratios B ψ 3686 → γ f 0 , 2 B J / ψ → γ f 0 , 2 $$ \frac{\mathcal{B}\left(\psi (3686)\to \gamma {f}_{0,2}\right)}{\mathcal{B}\left(J/\psi \to \gamma {f}_{0,2}\right)} $$ are determined, which provides crucial experimental inputs on the internal structure of the f 0,2 states, especially their potential mixing with glueball components.

Utilizing a dataset of 6.7 fb−1 from electron-positron collisions recorded by the BESIII detector at the BEPCII storage ring, a search is conducted for the processes e+e−→ϕχc0 and ϕηc2(1D) across center-of-mass energies from 4.47 to 4.95 GeV. In the absence of any significant signals, upper limits are set. These include limits on the dressed cross sections for e+e−→ϕχc0, as well as the product of the dressed cross section for e+e−→ϕηc2(1D) and a sum of five branching fractions. Furthermore, the product of the electronic width of Y(4660) and the branching fraction of the Y(4660)→ϕχc0, denoted as Γe+e−Y(4660)BY(4660)→ϕχc0, is determined to be <0.35 eV at the 90% confidence level. Published by the American Physical Society 2025

We measure the time-integrated CP asymmetry, A_CP, in D^0^0π^0 decays reconstructed in e^+e^-→ cc̅ events collected by Belle II during 2019–2022. The data corresponds to an integrated luminosity of 428fb^-1. The D^0 decays are required to originate from the flavor-conserving D^*+→ D^0 π^+ decay to determine the charm flavor at production time. Control samples of D^0→ K^- π^+ decays, with or without an associated pion from a D^*+ decay, are used to correct for detection asymmetries. The result, A_CP(D^0^0π^0) = (0.30± 0.72± 0.20)%, where the first uncertainty is statistical and the second systematic, is consistent with CP symmetry.

The process e^+e^-→K_S^0K_S^0ψ (3686) is studied by analyzing e+e− collision data samples collected at eight center-of-mass energies ranging from 4.682 to 4.951 GeV with the BESIII detector operating at the BEPCII collider, corresponding to an integrated luminosity of 4.1 fb−1. Observation of the e^+e^-→K_S^0K_S^0ψ (3686) process is found for the first time with a statistical significance of 6.3σ, and the cross sections at each center-of-mass energy are measured. The ratio of cross sections of e^+e^-→K_S^0K_S^0ψ (3686) relative to e+e− → K+K−ψ(3686) is determined to be σ(e^+e^-→K_S^0K_S^0ψ (3686))/σ(e^+e^-→K^+K^-ψ (3686))=0.45± 0.25 , which is consistent with the prediction based on isospin symmetry. The uncertainty includes both statistical and systematic contributions. Additionally, the K_S^0ψ (3686) invariant mass distribution is found to be consistent with three-body phase space. The significance of a contribution beyond three-body phase space is only 0.8σ.

Using 7.9fb−1 of e+e− collision data collected at s=3.773 GeV with the BESIII detector at the BEPCII collider, we search for the massless dark photon with the flavor-changing neutral current processes D0→ωγ′ and D0→γγ′ for the first time. No significant signals are observed, and the upper limits at the 90% confidence level on the massless dark photon branching fraction are set to be 1.1×10−5 and 2.0×10−6 for D0→ωγ′ and D0→γγ′, respectively. These results provide the most stringent constraint on the new physics energy scale associated with cuγ′ coupling in the world, with the new physics energy scale related parameter |C|2+|C5|2<8.2×10−17 GeV−2 at the 90% confidence level. Published by the American Physical Society 2025

A partial-wave analysis is performed on the decay J/ψ^0π^0π^0 within the π^0π^0π^0 invariant-mass region below 1.6 GeV/c^2, using (10.09 ± 0.04)×10^9 J/ψ events collected with the BESIII detector. Significant isospin-violating decays of η(1405) and f_1(1420) into f_0(980)π^0 are observed. For the first time, three axial-vectors, f_1(1285), f_1(1420) and f_1(1510), are observed to decay into π^0π^0π^0. The product branching fractions of these resonances are reported.

Based on (2712.4±14.1)×106 ψ(3686) decays collected with the BESIII detector, we have observed, for the first time, the hadronic decays of S- and P-wave charmonium states into 2(π+π−)η via radiative transitions from ψ(3686). The branching fraction of the decay ηc(1S)→2(π+π−)η has a significant dependence on the interference pattern between ηc(1S) and non-ηc(1S) processes. We measure it in both the destructive and constructive interference scenarios for the first time. The mass and width of the ηc(1S) are measured to be M=(2984.14±0.13±0.38) MeV/c2 and Γ=(28.82±0.11±0.82) MeV, respectively. Clear signals for the decays of the χcJ(J=0,1,2) and the ηc(2S) to 2(π+π−)η are also observed for the first time, and the corresponding branching fractions are measured. The ratio of the branching fractions between the ηc(2S) and ηc(1S) decays is significantly lower than the theoretical prediction, which might suggest different dynamics in their decays. Published by the American Physical Society 2025

By analyzing $(2712.4\pm14.3)\times10^6$ $\psi(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decays $\chi_{c0,1,2} \to 3K_S^0K^\pm\pi^\mp$ are observed for the first time with statistical significances greater than $10\sigma$. The branching fractions of these decays are determined to be $\mathcal{B}(\chi_{c0}\to 3K_S^0K^\pm\pi^\mp )=(7.95\pm0.50\pm0.65)\times10^{-5},$ $\mathcal{B}(\chi_{c1}\to 3K_S^0K^\pm\pi^\mp)=(2.62\pm0.08\pm0.19)\times10^{-4},$ and $\mathcal{B}(\chi_{c2}\to 3K_S^0K^\pm\pi^\mp)=(1.72\pm0.07\pm0.15)\times10^{-4},$ where the first uncertainties are statistical and the second systematic.

We report a search for an axion-like particle $a$ in $B\rightarrow K^{(*)} a (\rightarrow\gamma\gamma)$ decays using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. The search is based on a $711 \mathrm{fb^{-1}}$ data sample collected at the $\Upsilon 4S$ resonance energy, corresponding to a sample of $772\times10^6$ $\Upsilon 4S$ events. In this study, we search for the decay of the axion-like particle into a pair of photons, $a \rightarrow \gamma\gamma$. We scan the two-photon invariant mass in the range $0.16\ \mathrm{GeV/}c^2-4.50\ \mathrm{GeV}/c^2$ for the $K$ modes and $0.16\ \mathrm{GeV/}c^2-4.20\ \mathrm{GeV}/c^2$ 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 $3 \times 10^{-6} \mathrm{GeV}^{-1}$ to $3 \times 10^{-5} \mathrm{GeV}^{-1}$, improving the current constraints on $g_aW$ by a factor of two over the most stringent previous experimental results.

The Belle II experiment's ability to identify particles critically affects the sensitivity of its measurements. We describe Belle II's algorithms for identifying charged particles and evaluate their performance in separating pions, kaons, and protons using 426 fb(-1) of data collected at the energy-asymmetric e(+)e(-) collider SuperKEKB in 2019-2022 at center-of-mass energies at and near the mass of the gamma(4S).

Inelastic dark matter models that have two dark matter particles and a massive dark photon can reproduce the observed relic dark matter density without violating cosmological limits. The mass splitting between the two dark matter particles χ_{1} and χ_{2}, with m(χ_{2})>m(χ_{1}), is induced by a dark Higgs field and a corresponding dark Higgs boson h^{'}. We present a search for dark matter in events with two vertices, at least one of which must be displaced from the interaction region, and missing energy. Using a 365  fb^{-1} data sample collected at Belle II, which operates at the SuperKEKB e^{+}e^{-} collider, we observe no evidence for a signal. We set upper limits on the product of the production cross section σ(e^{+}e^{-}→h^{'}χ_{1}χ_{2}), and the product of branching fractions B(χ_{2}→χ_{1}e^{+}e^{-})×B(h^{'}→x^{+}x^{-}), where x^{+}x^{-} indicates μ^{+}μ^{-},π^{+}π^{-}, or K^{+}K^{-}, as functions of h^{'} mass and lifetime at the level of 10^{-1}  fb. We set model-dependent upper limits on the dark Higgs mixing angle at the level of 10^{-5} and on the dark photon kinetic mixing parameter at the level of 10^{-3}. This is the first search for dark Higgs bosons in association with inelastic dark matter.

We report a precise measurement of the ratio of branching fractions ℬ(Λ_c^+→ p K_S^0 π^0)/ℬ(Λ_c^+→ p K^- π^+) using 980 fb^-1 of e^+e^- data from the Belle experiment. We obtain a value of ℬ(Λ_c^+→ p K_S^0 π^0)/ℬ(Λ_c^+→ p K^- π^+)=0.339± 0.002± 0.009, where the first and second uncertainties are statistical and systematic, respectively. This Belle result is consistent with the previous measurement from the CLEO experiment but has a fivefold improvement in precision. By combining our result with the world average ℬ(Λ_c^+→ p K^- π^+), we obtain the absolute branching fraction ℬ(Λ_c^+→ p K_S^0 π^0)=(2.12± 0.01± 0.05 ± 0.10)%, where the uncertainties are statistical, systematic, and the uncertainty in the absolute branching fraction scale ℬ(Λ_c^+→ p K^- π^+), respectively. This measurement can shed light on hadronic decay mechanisms in charmed baryon decays.