Compared to charmonium-like states, exotic hadrons associated with b-quark offer distinct advantages for exploring the nature of multiquark phenomena and the dynamics of the strong interaction. Due to the heavier bottom quark mass, theoretical calculations, particularly those based on effective field theories and potential models, tend to be more reliable and under better control in the bottomonium sector. With its clean e+e− collision environment and high luminosity, the Belle and Belle II experiments are ideally suited to explore these exotic hadrons associated with b-quark, including Zb, Xb, and Yb states, and charmonium-like states in B decays. Utilizing the large proton–proton collision dataset, the LHCb experiment has conducted extensive investigations of heavy-flavor multiquark states through B and Λb decay channels. The relevant phenomenological interpretations are also reviewed.

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the Z pole, the expected production of 4 Tera Z bosons will provide unique and highly precise measurements of Z boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean Z decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and tau physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The WW threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals. The role of machine learning for innovative detector design and advanced reconstruction algorithms is also stressed. The CEPC flavor physics program not only develops new capabilities for exploring flavor physics beyond existing projects but also enriches the physics opportunities of this machine. It should be remarked that, given the richness of the CEPC flavor physics, this manuscript is not meant to be a comprehensive survey, but rather an investigation of representative cases. Uncovering the full potential of flavor physics at the CEPC will require further dedicated explorations in the future.

Based on 6.1  fb^{-1} of e^{+}e^{-} annihilation data collected at center-of-mass energies from 4.600 to 4.843 GeV with the BESIII detector at the BEPCII collider, a partial wave analysis of Λ_{c}^{+}→Λπ^{+}η is performed, and branching fractions and decay asymmetry parameters of intermediate processes are determined. The process Λ_{c}^{+}→Λa_{0}(980)^{+} is observed for the first time, and evidence for the pentaquark candidate Σ(1380)^{+} decaying into Λπ^{+} is found with statistical significance larger than 3σ with mass and width fixed to theoretical predictions. The branching fraction product B[Λ_{c}^{+}→Λa_{0}(980)^{+}]B[a_{0}(980)^{+}→π^{+}η] is determined to be (1.05±0.16_{stat}±0.05_{syst}±0.07_{ext})%, which is larger than theoretical calculations by 1-2 orders of magnitude. Here the third (external) systematic is from B(Λ_{c}^{+}→Λπ^{+}η). Finally, we precisely obtain the absolute branching fraction B(Λ_{c}^{+}→Λπ^{+}η)=(1.94±0.07_{stat}±0.11_{syst})%.

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^+) .

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

The Belle is a detector operating at the KEK electron-positron collider (KEKB) at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan. Belle II is an enhanced iteration of the Belle experiment, operating at the superKEKB electron-positron collider, which achieves the highest instantaneous luminosity. Belle and Belle II experiments can generate a vast quantity of B-meson data at and near the & upsih;(4S) resonance peak, which is why they are also known as the B factory. The BaBar, located at Stanford University, USA, and Belle experiments confirmed the Kobayashi-Masakawa theory by discovering the CP violation in the B meson system, and thus Kobayashi and Masakawa were awarded the Nobel Prize in Physics in 2008. Furthermore, the B-factory has demonstrated the value of utilising its vast data set for comprehensive research, leading to significant discoveries in diverse areas of particle physics. Notably, the Belle experiment observed the first hadronic state with exotic properties, the X(3872), in 2003. This discovery opened a new chapter in the study of the exotic hadron states. The China Group of the Belle and Belle II experiments carried out a series of measurements on charmed hadrons, B mesons, exotic hadron states, bottomonium, new physics beyond the standard model, etc., and obtained important results, including the discovery of the tetraquark state Zc(3900), the precise measurement of the mixing of D meson, the first measurement of the absolute branching fraction of Xi c, and achieving the best sensitivity on the radiative decay to the light Higgs particle with tau+tau-final state, etc. This paper briefly reviews the physics research works conducted by the China Group of the Belle and Belle II experiments, and pays tribute to the 120th anniversary of the founding of Fudan University.

Based on a sample of (2712.4 ± 14.3) × 106 ψ(3686) events collected with the BESIII detector, a partial wave analysis of the decay ψ (3686)→ΛΣ^0π^0 + c.c. is performed to investigate Λ* and Σ* resonances in the π^0Σ^0 and π0Λ invariant mass distributions. Significant contributions are found from the Λ(1405), Λ(1520), Λ(1600), Λ(1670), Λ(1690), Λ(1800), Λ(1890), Λ(2325), Σ(1385), Σ(1660), Σ(1670), Σ(1750), and Σ(1910). The masses, widths, and production branching fractions for each component are determined. In addition, the branching fraction of ψ (3686)→ΛΣ^0π^0 + c.c. is measured to be (1.544 ± 0.013 ± 0.071) × 10−4 for the first time, where the first uncertainty is statistical and the second systematic.

A bstract Based on 7.33 fb − 1 of e + e − collision data collected by the BESIII detector operating at the BEPCII collider at center-of-mass energies from 4.128 to 4.226 GeV, a search for the Majorana neutrino ν m is conducted in the lepton-number-violating decays of $$ {D}_{\textrm{s}}^{+} $$ D s + → h − h 0 e + e + . Here, h − represents a K − or π − , and h 0 represents a π 0 , $$ {K}_S^0 $$ K S 0 or ϕ . No significant signal is observed, and the upper limits of their branching fractions at the 90% confidence level are determined to be $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → ϕπ − e + e + ) < 6 . 9 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → ϕK − e + e + ) < 9 . 9 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → $$ {K}_S^0 $$ K S 0 π − e + e + ) < 1 . 3 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → $$ {K}_S^0 $$ K S 0 K − e + e + ) < 2 . 9 × 10 − 5 , $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → π − π 0 e + e + ) < 2 . 9 × 10 − 5 and $$ \mathcal{B} $$ B ( $$ {D}_{\textrm{s}}^{+} $$ D s + → K − π 0 e + e + ) < 3 . 4 × 10 − 5 . The Majorana neutrino is searched for with different mass assumptions within the range [0 . 20 , 0 . 80] GeV /c 2 in the decay of $$ {D}_{\textrm{s}}^{+} $$ D s + → ϕe + ν m with ν m → π − e + , and the upper limits of the branching fractions at the 90% confidence level are at the level of 10 − 5 –10 − 2 , depending on the mass of the Majorana neutrino.

Exotic hadrons, beyond the conventional quark model, have been discovered over the past two decades. Investigating these states can lead to a deeper understanding of the nonperturbative dynamics of the strong interaction. In this review, we focus on the production of exotic hadrons in pp, pp̅ , and nuclear collisions. Experimental observations of light and hypernuclei as prototypes of hadronic molecules in heavy-ion collisions are also briefly discussed.

We explore toponium, the smallest known quantum bound state of a top quark and its antiparticle, bound by the strong force. With a Bohr radius of 8 x 10-18 m and a lifetime of 2.5 x 10-25 s, toponium uniquely probes microphysics. Unlike all other hadrons, it is governed by ultraviolet freedom. This distinction offers novel insights into quantum chromodynamics. Our analysis reveals a toponium signal exceeding 5 sigma in the distribution of the cross section ratio between e+e- -* bb and e+e- -* qq (q = b, c, s, d, u), based on 400 fb-1 of data collected at ffiffi s p approximate to 341 GeV. This discovery enables a top quark mass measurement with an uncertainty reduced by a factor of ten compared to current precision levels. Moreover, this method improves the systematic uncertainty by at least a factor of 2.7 compared to any other possible methods.

Abstract Based on a data sample of (10087 ± 44) × 106 J/ψ events taken with the BESIII detector, we search for the flavor-changing neutral current charmonium decay J/ψ → D 0 μ + μ − + c.c. . No significant signal above the background is observed, and the upper limit on its branching fraction is set to be ℬ(J/ψ → D 0 μ + μ − + c.c.) < 1.1 × 10 −7 at the 90% confidence level. This marks the first search for a flavor-changing neutral current charmonium decay involving muons in the final state.

A bstract By analyzing e + e − collision data with an integrated luminosity of 7.9 fb − 1 collected with the BESIII detector at the center-of-mass energy of 3.773 GeV, the branching fraction of D + → τ + ν τ is determined as $$ \mathcal{B} $$ B = (9.9 ± 1.1 stat ± 0.5 syst ) × 10 − 4 . Using the most precise result $$ \mathcal{B} $$ B ( D + → μ + ν μ ) = (3.981 ± 0.079 stat ± 0.040 syst ) × 10 − 4 [1], we determine R τ/μ = Γ( D + → τ + ν τ )/Γ( D + → μ + ν μ ) = 2.49 ± 0.31, achieving a factor of two improvement in precision compared to the previous BESIII result. This measurement is in agreement with the standard model prediction of lepton flavor universality within one standard deviation.

We measure the Born cross section for the reaction e+e−→ηhc from s=4.129 to 4.600 GeV using datasets collected by the BESIII detector running at the BEPCII collider. A resonant structure in the cross-section line shape near 4.200 GeV is observed with a statistical significance of 7σ. The parameters of this resonance are measured to be M=4188.8±4.7±8.0 MeV/c2 and Γ=49±16±19 MeV, where the first uncertainties are statistical and the second systematic. Published by the American Physical Society 2025

Based on (2712.4 ± 14.3) × 106 ψ(3686) events collected at the BESIII detector operating at the BEPCII collider, we present the first observation of the decay ψ (3686)→K^-Λ (1520)Ξ^+ + c.c.. The product branching fraction ℬ[ψ (3686)→K^-Λ (1520)Ξ^++c.c.]×ℬ[Λ (1520)→ pK^-] is measured to be (9.47 ± 0.75 ± 0.97) × 10−7, where the first uncertainty is statistical and the second systematic.

Electron–positron colliders operating in the GeV center-of-mass range, or tau-charm energy region, have been proved to enable competitive frontier research due to several unique features. With the progress of high-energy physics in the last two decades, a new-generation Tau-Charm factory, called the Super Tau-Charm Facility (STCF), has been actively promoted by the particle physics community in China. STCF has the potential to address fundamental questions such as the essence of color confinement and the matter–antimatter asymmetry within the next decades. The main design goals of the STCF are a center-of-mass energy ranging from 2 to 7 GeV and a luminosity surpassing 5 × 1034 cm−2 s−1 that is optimized at a center-of-mass energy of 4 GeV, which is approximately 50 times that of the currently operating Tau-Charm factory—BEPCII. The STCF accelerator has two main parts: a double-ring collider with a crab-waist collision scheme and an injector that provides top-up injections for both electron and positron beams. As a typical third-generation electron–positron circular collider, the STCF accelerator faces many challenges in both accelerator physics and technology. In this paper, the conceptual design of the STCF accelerator complex is presented, including the ongoing efforts and plans for technological research and development, as well as the required infrastructure. The STCF project aims to secure support from the Chinese central government for its construction during the 15th Five-Year Plan (2026–2030).

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 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 perform the first amplitude analysis of D_{s}^{+}→π^{+}π^{+}π^{-}π^{0} decays based on data samples of electron-positron collisions recorded with the BESIII detector at center-of-mass energies between 4.128 and 4.226 GeV, corresponding to an integrated luminosity of 7.33  fb^{-1}. We report the observation of D_{s}^{+}→f_{0}(980)ρ(770)^{+} with a statistical significance greater than 10σ and determine the branching fractions B(D_{s}^{+}→π^{+}π^{+}π^{-}π^{0}|_{non-η})=(2.04±0.08_{stat}±0.05_{syst})% and B(D_{s}^{+}→ηπ^{+})=(1.56±0.09_{stat}±0.04_{syst})%. Moreover, we measure the relative branching fraction between ϕ→π^{+}π^{-}π^{0} and ϕ→K^{+}K^{-} to be [B(ϕ(1020)→π^{+}π^{-}π^{0})/B(ϕ(1020)→K^{+}K^{-})]=0.230±0.014_{stat}±0.010_{syst}., which deviates from the world average value by more than 4σ.

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 $${f}_{s}=\left({21.4}_{-1.7}^{+1.5}\right)\%$$ .