Belle Experiment Research Articles

Search for the Σ(1380)1/2− state in Λc+→γπ+Λ decay by triangle singularity

In this work, we investigate the resonance production in Λc+→γπ+Λ decay through the triangle singularity (TS) mechanism, within an effective Lagrangian approach. We find that the appropriate loop decay process could develop a triangle singularity in the invariant mass MπΛ around 1.35 GeV, with the shape depending on the quantum numbers of Σ* states that couple to the final πΛ system. Especially, the Σ(1380)1/2− state newly predicted in the pentaquark model, if exists, significantly enhances the TS contribution and sharpens the TS peak due to the S-wave Σ*πΣ vertex in the loop. Therefore, the existence of the Σ(1380)1/2− state can be examined by measuring the TS signal in Λc+→γπ+Λ. Considering also possible tree-level diagrams, we additionally obtain the branching ratio Br(Λc+→γπ+Λ)≃1.5×10−5. We suggest the investigation of this reaction by future BESIII, LHCb, and Belle experiments. Published by the American Physical Society 2024

Determination of the CKM angle ϕ3 from a combination of Belle and Belle II results

We report a determination of the CKM angle ϕ3, 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 D0 and D¯0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\overline{D}}^0 $$\\end{document} mesons, in a likelihood fit to obtain ϕ3 = (75.2 ± 7.6)°. We also briefly discuss the interpretation of this result.

Unbounded Sharing of Nonlocality Using Qubit Projective Measurements.

The prevailing consensus is that the sequential sharing of nonlocality in a Bell experiment requires generalized unsharp measurements, given that a sharp measurement inevitably destroys the entanglement of the shared state. In contrast, a recent work [A. Steffinlongo and A. Tavakoli, Projective measurements are sufficient for recycling nonlocality, Phys. Rev. Lett. 129, 230402 (2022)PRLTAO0031-900710.1103/PhysRevLett.129.230402] demonstrated the sharing of nonlocality up to two sequential observers by employing projective measurement aided with local randomness. Here, we introduce a form of local randomness-assisted qubit projective measurement protocol that enables the sharing of nonlocality by an arbitrary number of sequential observers (Bobs) with a single spatially separated observer (Alice). We achieve this by inspecting the diversity involved in implementing generalized measurements that harness nonlocality by preserving a sufficient amount of entanglement of the shared two-qubit entangled state. Furthermore, we highlight the crucial interplay between the degrees of measurement incompatibility of Alice and Bob in demonstrating the unbounded sharing of nonlocality.

Recent highlights from the BELLE and BELLE II experiments

The BELLE experiment at the KEKB collider in Tsukuba operated as a B-factory until 2018, making significant contributions to flavor physics. Building on this legacy, the BELLE II experiment, an upgraded version, now operates at the SuperKEKB energy-asymmetric e+e− collider. BELLE II has collected 424fb−1 of data, including 365fb−1 at the ϒ(4S) resonance. A wide range of physics topics can be studies with this data. In this proceeding, we review our latest results, which include tests of lepton flavor universality, Cabibbo-Kobayashi-Maskawa physics, searches for rare B-meson decays, and spectroscopy studies. We also discuss contributions to the gμ−2 prediction.

Information Causality as a Tool for Bounding the Set of Quantum Correlations.

Information causality was initially proposed as a physical principle aimed at deriving the predictions of quantum mechanics on the type of correlations observed in the Bell experiment. In the same work, information causality was famously shown to imply the Uffink inequality that approximates the set of quantum correlations and rederives Tsirelson's bound of the Clauser-Horne-Shimony-Holt inequality. This result found limited generalizations due to the difficulty of deducing implications of the information causality principle on the set of nonlocal correlations. In this Letter, we present a simple technique for obtaining polynomial inequalities from information causality bounding the set of physical correlations in any bipartite Bell scenario. This result makes information causality an efficient tool for approximating the set of quantum correlations. To demonstrate our method, we derive a family of inequalities which nontrivially constrains the set of nonlocal correlations in Bell scenarios with binary outcomes and equal number of measurement settings. Finally, we propose an improved statement of the information causality principle and obtain a tighter constraint for the simplest Bell scenario that goes beyond the Uffink inequality and recovers a part of the boundary of the quantum set.

(J/ψ,J/ψ), and (ηc,ηc) production through two intermediate photons in electron-positron annihilation at B-factories

We study the processes, e−e+→γ⁎γ⁎→J/ψ+J/ψ, and e−e+→γ⁎γ⁎→ηc+ηc at s=10.6 GeV in the framework of 4×4 Bethe-Salpeter equation. For J/ψ+J/ψ production, the dominant contribution is through fragmentation process, while for ηc+ηc production, the quark rearrangement diagrams contribute. Our results of cross section for J/ψ+J/ψ and ψ(2S)+ψ(2S) are compatible with the experimental upper limits set by Belle Collaboration, while in the absence of experimental data for ηc(1S)+ηc(1S), and ηc(2S)+ηc(2S) production, we have given theoretical prediction of their cross sections, and compared with NRQCD prediction.

Su(3) symmetry analysis in charmed baryon two body decays with penguin diagram contribution

An increasing number of experimental measurements from the BESIII, Belle, and Belle-II collaborations encourage investigations into charmed baryon two-body decay processes. By including contributions from the penguin diagrams that are ignored in previous studies, we perform a global analysis with SU(3) flavor symmetry. Assuming all form factors are real, we achieve a remarkable minimal χ2/d.o.f=0.788\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\chi ^{2}/d.o.f = 0.788$$\\end{document} and find that the contribution of the amplitude proportional to Vcb∗Vub\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_{cb}^*V_{ub}$$\\end{document} is of the order ∼0.01\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim 0.01$$\\end{document}, comparable with the contribution of the tree-level diagram. Additionally, by using the KPW theorem to reduce the number of amplitudes from 13 to 7 in the leading contribution, it becomes possible to consider the complex form factor case for the leading IRA amplitude in the global analysis. However, the analysis of complex form factors significantly conflicts with the experimental data Br(Ξc0→Ξ-π+)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Br(\\Xi _c^0\\rightarrow \\Xi ^-\\pi ^+)$$\\end{document}, and by excluding this data, χ2/d.o.f\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\chi ^2/d.o.f$$\\end{document} is reduced from 5.95 to 1.19. Although the analysis of complex form factors shows a significant central value of the penguin diagram contribution, the large errors from the corresponding form factors make it a challenge to precisely determine its true contribution. Consequently, the direct CP violation in decay processes is predicted to be approximately zero. With more data in future experiments, the penguin diagram contribution with the amplitude proportional to Vcb∗Vub\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_{cb}^*V_{ub}$$\\end{document} will be precisely determined, allowing for a more accurate prediction of CP violation. Our analysis necessitates further theoretical investigations and experimental measurements in the future.

Measurement of the Michel parameters in leptonic τ-decays at Super Tau-Charm facility

We present a new method for direct measurement of all Michel parameters in the [Formula: see text] decay related to the polarization of the daughter muon: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]. The method is based on the reconstruction of the muon decays-in-flight in the tracker of the [Formula: see text] collider experiments and relies on the correlation between muon spin and its daughter electron momentum. The low probability of decay-in-flight in the tracker volume is compensated by the unprecedented statistics of modern flavor factories, which ultimately leads to the possibility of achieving high accuracy. We discuss the application of the suggested method in the experiments at [Formula: see text] colliders and present a feasibility study for the future Super Charm-Tau Factory experiment. We also discuss the result of the first use of the proposed method in the Belle experiment, confirming its applicability.

Deriving Three-Outcome Permutationally Invariant Bell Inequalities.

We present strategies to derive Bell inequalities valid for systems composed of many three-level parties. This scenario is formalized by a Bell experiment with N observers, each of which performs one out of two possible three-outcome measurements on their share of the system. As the complexity of the set of classical correlations prohibits its full characterization in this multipartite scenario, we consider its projection to a lower-dimensional subspace spanned by permutationally invariant one- and two-body observables. This simplification allows us to formulate two complementary methods for detecting nonlocality in multipartite three-level systems, both having a complexity independent of N. Our work can have interesting applications in the detection of Bell correlations in paradigmatic spin-1 models, as well as in experiments with solid-state systems or atomic ensembles.

Investigation of vertex a1>>VP for hadronic tau decays

In the framework of U(3) symmetric quark model, triangular diagrams are calculated that describe the strongly interacting vertices a1>>rhopi and a1>>K*K. The divergences arising when considering quark loops are regularized by covariant cutoff parameter. Based on four-particle hadronic τ decays, the quark structure of the resonance with quantum numbers JPC=1++ was studied. Theoretical estimates of intermediate channels with the meson for the partial decay widths of tau>>pipipinu, tau>>KKpinu and tau>>KKetanu are obtained. Contributions from contact channels describing the direct production of 3pi, KKpi and KKeta mesons by τ lepton current are taken into account. The interference of contact and intermediate axial-vector channels in determining the integral decay widths is studied. The matrix elements of the processes are obtained in the leading approximation of 1/Nc expansion. It is shown that calculations on τ lepton mesonic decays confirm the quark-antiquark structure of the a1 meson and clarify the role of the intermediate non-strange axial-vector channel in determining the integral partial decay widths. The obtained results are compared with experimental data by BaBar and Belle collaborations at the BEPC II and KEK lepton colliders.

Strong decays of the Λc(2910) and Λc(2940) in the ND* molecular frame

Stimulated by the observation of a new structure, named Λc(2910), in the Σc(2455)0,++π+,− decay channel from B meson decay process by the Belle Collaboration, and the similarity of the Λc(2910)/Λc(2940) and Pc states, we investigate the decay behavior of the Λc(2910) and Λc(2940) in the ND* molecular frame with the possible JP quantum numbers to be 1/2− and 3/2−. We employ an effective Lagrangian approach to evaluate the partial widths of ND, Σcπ, and Σc*π channels. The estimations in the present work indicate that the JP quantum numbers of Λc(2910) and Λc(2940) are preferred to be 1/2− and 3/2−, respectively. From the present estimations, we also find the branching ratio of Λc(3/2)→Σc*π is much larger than that of Λc(1/2)→Σc*π, thus Σc*π could be a good channel to distinguish the JP quantum numbers of Λc(2910) and Λc(2940). Therefore, we suggest searching for the structure in Σc*π invariant mass distribution in Belle II. Published by the American Physical Society 2024

Certifying long-range quantum correlations through routed Bell tests

Losses in the transmission channel, which increase with distance, pose a major obstacle to photonics demonstrations of quantum nonlocality and its applications. Recently, Chaturvedi, Viola, and Pawlowski (CVP) [arXiv:2211.14231] introduced a variation of standard Bell experiments with the goal of extending the range over which quantum nonlocality can be demonstrated. These experiments, which we call `routed Bell experiments', involve two distant parties, Alice and Bob, and allow Bob to route his quantum particle along two possible paths and measure it at two distinct locations – one near and another far from the source. The premise is that a high-quality Bell violation in the short-path should constrain the possible strategies underlying the experiment, thereby weakening the conditions required to detect nonlocal correlations in the long-path. Building on this idea, CVP showed that there are certain quantum correlations in routed Bell experiments such that the outcomes of the remote measurement device cannot be classically predetermined, even when its detection efficiency is arbitrarily low. In this paper, we show that the correlations considered by CVP, though they cannot be classically predetermined, do not require the transmission of quantum systems to the remote measurement device. This leads us to define and formalize the concept of `short-range' and `long-range' quantum correlations in routed Bell experiments. We show that these correlations can be characterized through standard semidefinite-programming hierarchies for non-commutative polynomial optimization. We then explore the conditions under which short-range quantum correlations can be ruled out and long-range quantum nonlocality can be certified in routed Bell experiments. We point out that there exist fundamental lower-bounds on the critical detection efficiency of the distant measurement device, implying that routed Bell experiments cannot demonstrate long-range quantum nonlocality at arbitrarily large distances. However, we do find that routed Bell experiments allow for reducing the detection efficiency threshold necessary to certify long-range quantum correlations. The improvements, though, are significantly smaller than those suggested by CVP's analysis.

Experimental sharing of Bell nonlocality with projective measurements

In the standard Bell experiment, two parties perform local projective measurements on a shared pair of entangled qubits to generate nonlocal correlations. However, these measurements completely destroy the entanglement, rendering the post-measurement state unable for subsequent use. For a long time, it was believed that only unsharp measurements can be used to share quantum correlations. Remarkably, recent research has shown that classical randomness assisted projective measurements are sufficient for sharing nonlocality (Steffinlongo and Tavakoli 2022 Phys. Rev. Lett. 129 230402). Here, by stochastically combining no more than two different projective measurement strategies, we report an experimental observation of double Clauser–Horne–Shimony–Holt inequality violations with two measurements in a sequence made on each pair of maximally and partially entangled polarization photons. Our results reveal that the double violation achieved by partially entangled states can be 11 standard deviations larger than that achieved by maximally entangled ones. Our scheme eliminates the requirement for entanglement assistance in previous unsharp-measurement-based sharing schemes, making it experimentally easier. Our work provides possibilities for sharing other types of quantum correlations in various physical systems with projective measurements.

Analysis of strong decays of SU(3) partners of Ω(2012) baryon

We estimate the coupling constants and decay widths of the partners of the hyperon, as discovered by the BELLE Collaboration, using the distribution amplitudes of the octet baryons within the light cone sum rules method. Our study includes a comparison of the obtained results for the relevant decay widths with those derived within the framework of the flavor analysis. We observe a good agreement between the predictions of both approaches. Moreover, our result on the decay width of is compatible with the existing experimental result within the uncertainties of the model predictions. These results can provide helpful insights for determining the nature of the partners of the baryon.

New physics couplings from angular coefficient functions of B¯→D*(Dπ)ℓν¯ℓ

The Belle Collaboration has recently measured the complete set of angular coefficient functions for the exclusive decays B¯→D*(Dπ)ℓν¯ℓ, with ℓ=e, μ, in four bins of the parameter w=mB2+mD*2−q22mBmD*, with q the lepton pair momentum [M. T. Prim (Belle Collaboration), ]. Under the assumption that physics beyond the Standard Model does not contribute to such modes, the measurements are useful to determine the hadronic form factors describing the B→D* matrix elements of the Standard Model weak current, and to improve the determination of |Vcb|. On the other hand, they can be used to assess the impact of possible new physics contributions. In a bottom-up approach, we extend the Standard Model effective Hamiltonian governing this mode with the inclusion of the full set of Lorentz invariant d=6 operators compatible with the gauge symmetry of the theory. The measured angular coefficient functions can tightly constrain the couplings in the generalized Hamiltonian. We present the first results of this analysis, discussing how improvements can be achieved when more complete data on the angular coefficient functions will be available. Published by the American Physical Society 2024

B→D*ℓνℓ semileptonic form factors from lattice QCD with Möbius domain-wall quarks

We calculate the form factors for the B→D*ℓνℓ decay in 2+1 flavor lattice QCD. For all quark flavors, we employ the Möbius domain-wall action, which preserves chiral symmetry to a good precision. Our gauge ensembles are generated at three lattice cutoffs a−1∼2.5, 3.6, and 4.5 GeV with pion masses as low as Mπ∼230 MeV. The physical lattice size L satisfies the condition MπL≥4 to control finite volume effects (FVEs), while we simulate a smaller size at the smallest Mπ to directly examine FVEs. The bottom quark masses are chosen in a range from the physical charm quark mass to 0.7a−1 to control discretization effects. We extrapolate the form factors to the continuum limit and physical quark masses based on heavy meson chiral perturbation theory at next-to-leading order. Then the recoil parameter dependence is parametrized using a model independent form leading to our estimate of the decay rate ratio between the tau (ℓ=τ) and light lepton (ℓ=e, μ) channels R(D*)=0.252(22) in the Standard Model. A simultaneous fit with recent data from the Belle experiment yields |Vcb|=39.19(91)×10−3, which is consistent with previous exclusive determinations, and shows good consistency in the kinematical distribution of the differential decay rate between the lattice and experimental data. Published by the American Physical Society 2024

Determination of the resonant parameters of with global fit*

Abstract Particle was first observed by the Belle experiment in the invariant mass spectrum in the process and subsequently confirmed by the BaBar experiment. Both experiments reported the resonant parameters of this particle in the processes and assuming as an S-wave Breit-Wigner resonance. We performed a global fit to the distributions of invariant mass of measured by the Belle and BaBar experiments and additionally incorporated the measurements reported by the LHCb experiment to extract the mass and width of . We obtained MeV/ and MeV, which are consistent with the values from PDG within one standard deviation but with higher precision.

Production of the X(4014) as the Spin-2 Partner of X(3872) in e + e − Collisions

In 2021, the Belle collaboration reported the first observation of a new structure in the ψ(2S)γ final state produced in the two-photon fusion process. In the hadronic molecule picture, this new structure can be associated with the shallow isoscalar D*D¯* bound state and as such is an excellent candidate for the spin-2 partner of the X(3872) with the quantum numbers J PC = 2++ conventionally named X 2. In this work we evaluate the electronic width of this new state and argue that its nature is sensitive to its total width, the experimental measurement currently available being unable to distinguish between different options. Our estimates demonstrate that the planned Super τ-Charm Facility offers a promising opportunity to search for and study this new state in the invariant mass distributions for the final states J/ψγ and ψ(2S)γ.

Erratum: Kolmogorov complexity of sequences of random numbers generated in Bell's experiments [Phys. Rev. A 98 , 042131 (2018)

Erratum: Kolmogorov complexity of sequences of random numbers generated in Bell's experiments [Phys. Rev. A <b>98</b> , 042131 (2018)

Search for the decay Bs0→J/ψπ0 at Belle experiment

We have analyzed 121.4 fb−1 of data collected at the ϒ(5S) resonance by the Belle experiment using the KEKB asymmetric-energy e+e− collider to search for the decay Bs0→J/ψπ0. We observe no signal and report an upper limit on the branching fraction B(Bs0→J/ψπ0) of 1.21×10−5 at 90% confidence level. This result is the most stringent, improving the previous bound by 2 orders of magnitude. Published by the American Physical Society 2024