Belle Experiment Research Articles

Optimal Statistical Analyses of Bell Experiments

We show how both smaller and more reliable p-values can be computed in Bell-type experiments by using statistical deviations from no-signalling equalities to reduce statistical noise in the estimation of Bell’s S or Eberhard’s J. Further improvement was obtained by using the Wilks likelihood ratio test based on the four tetranomially distributed vectors of counts of the four different outcome combinations, one 4-vector for each of the four setting combinations. The methodology was illustrated by application to the loophole-free Bell experiments of 2015 and 2016 performed in Delft and Munich, at NIST, and in Vienna, respectively, and also to the earlier (1998) Innsbruck experiment of Weihs et al. and the recent (2022) Munich experiment of Zhang et al., which investigates the use of a loophole-free Bell experiment as part of a protocol for device-independent quantum key distribution (DIQKD).

Study of double-charm and double-strange tetraquark Xccs¯s¯

In the framework of the quark delocalization color screening model, we search for the double-charm and double-strange tetraquark ${X}_{cc\overline{s}\overline{s}}$ with two structures: $Q\overline{q}\ensuremath{-}Q\overline{q}$ and $QQ\ensuremath{-}\overline{q}\overline{q}$. The bound-state calculation shows that there is no bound state in the present work. However, by applying a stabilization calculation and coupling all channels of both structures, two new resonance states with $I{J}^{P}=0{0}^{+}$ are obtained, one with mass and width around 4250 and 6 MeV, respectively, and another one with mass and width around 4300 and 19 MeV, respectively. Both of these states are more likely to be the compact resonance states. Although no significant signals were observed in the present experiment at the Belle Collaboration, there are still some structures around 4.3 GeV in the distributions of ${M}_{{D}_{s}^{+}{D}_{s}^{+}}$ and ${M}_{{D}_{s}^{*+}{D}_{s}^{*+}}$. We suggest that the experiment can be further tested with a larger amount of data.

Probing the structure of χc1(3872) with photon transition form factors

We propose studying the structure of the ${\ensuremath{\chi}}_{c1}(3872)$ axial vector meson through its ${\ensuremath{\gamma}}_{L}^{*}\ensuremath{\gamma}\ensuremath{\rightarrow}{\ensuremath{\chi}}_{c1}(3872)$ transition form factor. We derive a light-front wave function representation of the form factor for the lowest $c\overline{c}$ Fock state. We found that the reduced width of the state is well within the current experimental bound recently published by the Belle Collaboration. This strongly suggests a crucial role of the $c\overline{c}$ Fock-state in the photon-induced production. Our results for the ${Q}^{2}$ dependence can be tested by future single-tagged ${e}^{+}{e}^{\ensuremath{-}}$ experiments, giving further insight into the short-distance structure of this meson.

Further study of within a chiral quark model* *Supported by the National Natural Science Foundation of China (12175065, 12005060, 12075288, 11735003, 11961141012). Ju-Jun Xie is also supported by the Youth Innovation Promotion Association CAS

In our previous studies, we analyzed the two-body strong decays of the low-lying Ω baryon states within a chiral quark model. The results showed that the mass, total width, and two body decay could be well reproduced with the spin-parity state classified in the quark model. Stimulated by the new observations of the three-body decay process at Belle, in the present study, we further investigate the three-body strong decay within the chiral quark model. It is found that the has a sizeable decay rate into the three-body final states . When considering as the resonance, the predicted ratio is close to the upper limit measured by the Belle Collaboration in 2019; however, it is too small to be comparable to the recent measurement . In addition, the coupled-channel effects on the bare three-quark state from nearby channels , , and are studied. Our theoretical results show that the coupled-channel effects on are not very large, and the molecular component is no more than . To clarify the nature of resonance, precise measurements on the ratio are needed, and further investigation on the effects of coupled channels is recommended.

New insights into the pole parameters of the Λ(1380), the Λ(1405) and the Σ(1385)

A coupled-channel S- and P-wave next-to-leading order chiral-unitary approach for strangeness S = −1 meson-baryon scattering is extended to include the new data from the KLOE and AMADEUS experiments as well as the Λπ mass distribution of the Σ(1385). The positions of the poles on the second Riemann sheet corresponding to the Σ(1385) pole and the Λ(1380) and Λ(1405) poles as well as the couplings of these states to various channels are calculated. We find that the resonance positions and branching ratios are on average determined with about 20% higher precision when including the KLOE and AMADEUS data. Additionally, for the first time, the correlations between the parameters of the poles are investigated and shown to be relevant. We also find that the Σ(1385) has negligible influence on the properties of the Λ states given the available data. Still, we identify isospin-1 cusp structures in the present solution in light of new measurements of π±Λ line-shapes by the Belle collaboration.

Weak radiative decay Lambda _{c}^{+}rightarrow Sigma ^{+}gamma using light-cone sum rules

We calculate the decay width of the Lambda _{c}^{+}rightarrow Sigma ^{+}gamma using light-cone sum rules. For the initial quark radiation an effective Hamiltonian is constructed, where the internal quark line shrinks to a point. The final quark radiation is studied within the full theory. The leading twist light-cone distribution amplitudes of the Sigma ^+ serve as the non-perturbative input for the sum rules calculation, and the perturbative kernel is calculated at leading order. The branching fraction we obtain is mathcal{B}(Lambda _{c}^{+}rightarrow Sigma ^{+}gamma )=1.03pm 0.36 times 10^{-4}, which is below the recent upper limits <2.6 times 10^{-4} and <4.4 times 10^{-4} given by the Belle collaboration and the BESIII collaboration, respectively.

A mathematical framework for operational fine tunings

In the framework of ontological models, the inherently nonclassical features of quantum theory always seem to involve properties that are fine tuned, i.e. properties that hold at the operational level but break at the ontological level. Their appearance at the operational level is due to unexplained special choices of the ontological parameters, which is what we mean by a fine tuning. Famous examples of such features are contextuality and nonlocality. In this article, we develop a theory-independent mathematical framework for characterizing operational fine tunings. These are distinct from causal fine tunings – already introduced by Wood and Spekkens in [NJP,17 033002(2015)] – as the definition of an operational fine tuning does not involve any assumptions about the underlying causal structure. We show how known examples of operational fine tunings, such as Spekkens&amp;apos; generalized contextuality, violation of parameter independence in Bell experiment, and ontological time asymmetry, fit into our framework. We discuss the possibility of finding new fine tunings and we use the framework to shed new light on the relation between nonlocality and generalized contextuality. Although nonlocality has often been argued to be a form of contextuality, this is only true when nonlocality consists of a violation of parameter independence. We formulate our framework also in the language of category theory using the concept of functors.

Impact of Λb→Λcτν measurement on new physics in b→clν transitions

Measurements of the branching ratios of $B \to D^{(*)}\tau\bar\nu/B \to D^{(*)}\ell\bar\nu$ and $B_c\to J/\psi\, \tau\bar\nu/B_c\to J/\psi\, \ell\bar\nu$ by the BaBar, Belle and LHCb collaborations consistently point towards an abundance of taus compared to channels with light leptons. However, the ratio $\Lambda_b \to\Lambda_c \tau\bar\nu/\Lambda_b \to\Lambda_c \ell\bar\nu$ shows a relative deficit in taus. In this paper, we critically address whether data still points towards a coherent pattern of deviations, in particular in light of the sum rule relating these decays in a model-independent way. We find that no common new physics explanation of all ratios is possible (within $2\sigma$ or $1.5\sigma$, depending on the ${\cal R}(\Lambda_c)$ normalization to light lepton channels). While this inconsistency could be a statistical fluctuation, further measurements are required in order to converge to a coherent pattern of experimental results.

Measurement of the branching fraction and search for CP violation in D0→KS0KS0π+π− decays at Belle

We measure the branching fraction for the Cabibbo-suppressed decay D0→KS0KS0π+π− and search for CP violation via a measurement of the CP asymmetry ACP as well as the T-odd triple-product asymmetry aCPT. We use 922 fb−1 of data recorded by the Belle experiment, which ran at the KEKB asymmetric-energy e+e− collider. The branching fraction is measured relative to the Cabibbo-favored normalization channel D0→KS0π+π−; the result is B(D0→KS0KS0π+π−)=[4.79±0.08(stat)±0.10(syst)±0.31(norm)]×10−4, where the first uncertainty is statistical, the second is systematic, and the third is from uncertainty in the normalization channel. We also measure ACP=[−2.51±1.44(stat)−0.10+0.11(syst)]%, and aCPT=[−1.95±1.42(stat)−0.12+0.14(syst)]%. These results show no evidence of CP violation.Received 16 July 2022Accepted 30 January 2023DOI:https://doi.org/10.1103/PhysRevD.107.052001Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBranching fractionElectroweak interactionPhysical SystemsCharmed mesonsMesonsPropertiesCP violationParticles & Fields

Chiral Lagrangians for strong decays K1→Kρ(ω)

A triangular quark diagram describes the vertex K1Kω&nbsp;with axial-vector, vector, and pseudoscalar mesons is considered in the leading order of 1NC. The application of the obtained vertex to the hadronic decays of the τ-lepton with the production of&nbsp;Kω,&nbsp;Kφ &nbsp;meson pairs in the final state is discussed. Calculation of quark diagrams are considered within&nbsp;the &nbsp;SU(3) symmetric chiral Lagrangians, which describe the interactions of four meson nonets: scalar, pseudoscalar, vector, and axial-vector in the ground and in the first radially excited states. The calculated integral decay widths of K1(1270)→K[ω,ρ]&nbsp;are in the agreement with the experimental data of the BES-III and Belle collaborations obtained at the BEPC II and KEK colliders. It is shown that the axial-vector channel with the intermediate meson K1A&nbsp;with quantum numbers &nbsp;JPC=1++&nbsp;plays a dominant role in describing the decay widths of τ→K[ω,ρ]ντ. In &nbsp;lepton decays, the contact channel and the channel with the axial vector meson K1A&nbsp;are taken into account. The first of them is related with the intermediate&nbsp;W &nbsp;boson, which products a meson pair. The second channel is related with the intermediate W&nbsp;boson, which transits into the axial vector state K1A&nbsp;and also products meson pairs. Consideration of these two channels independently of each other allows us to study the processes in more detail. The splitting of the strange axial vector state K1A&nbsp;into two physical mesons&nbsp;K1(1270)&nbsp;and K1(1400) due to the mixing of axial vector mesons from nonets 3P1&nbsp;and &nbsp;1P1&nbsp;is also taken into account. The negative interference of the contact channel with the axial vector channel is established. The dependences of the integral decay widths of τ→K[ω,ρ]ντ&nbsp;on the value of the mixing angle of axial-vector mesons K1A&nbsp;and&nbsp;K1B&nbsp;are studied. A comparative analysis of the results with experimental data and theoretical estimates of other authors is carried out. The obtained theoretical predictions are in satisfactory agreement with the experimental data.

Experimental nonclassicality in a causal network without assuming freedom of choice

In a Bell experiment, it is natural to seek a causal account of correlations wherein only a common cause acts on the outcomes. For this causal structure, Bell inequality violations can be explained only if causal dependencies are modeled as intrinsically quantum. There also exists a vast landscape of causal structures beyond Bell that can witness nonclassicality, in some cases without even requiring free external inputs. Here, we undertake a photonic experiment realizing one such example: the triangle causal network, consisting of three measurement stations pairwise connected by common causes and no external inputs. To demonstrate the nonclassicality of the data, we adapt and improve three known techniques: (i) a machine-learning-based heuristic test, (ii) a data-seeded inflation technique generating polynomial Bell-type inequalities and (iii) entropic inequalities. The demonstrated experimental and data analysis tools are broadly applicable paving the way for future networks of growing complexity.

Graph-theoretic approach to Bell experiments with low detection efficiency

Bell inequality tests where the detection efficiency is below a certain threshold &amp;#x03B7;crit can be simulated with local hidden-variable models. Here, we introduce a method to identify Bell tests requiring low &amp;#x03B7;crit and relatively low dimension d of the local quantum systems. The method has two steps. First, we show a family of bipartite Bell inequalities for which, for correlations produced by maximally entangled states, &amp;#x03B7;crit can be upper bounded by a function of some invariants of graphs, and use it to identify correlations that require small &amp;#x03B7;crit. We present examples in which, for maximally entangled states, &amp;#x03B7;crit&amp;#x2264;0.516 for d=16, &amp;#x03B7;crit&amp;#x2264;0.407 for d=28, and &amp;#x03B7;crit&amp;#x2264;0.326 for d=32. We also show evidence that the upper bound for &amp;#x03B7;crit can be lowered down to 0.415 for d=16 and present a method to make the upper bound of &amp;#x03B7;crit arbitrarily small by increasing the dimension and the number of settings. All these upper bounds for &amp;#x03B7;crit are valid (as it is the case in the literature) assuming no noise. The second step is based on the observation that, using the initial state and measurement settings identified in the first step, we can construct Bell inequalities with smaller &amp;#x03B7;crit and better noise robustness. For that, we use a modified version of Gilbert's algorithm that takes advantage of the automorphisms of the graphs used in the first step. We illustrate its power by explicitly developing an example in which &amp;#x03B7;crit is 12.38&amp;#x0025; lower and the required visibility is 14.62&amp;#x0025; lower than the upper bounds obtained in the first step. The tools presented here may allow for developing high-dimensional loophole-free Bell tests and loophole-free Bell nonlocality over long distances.

Nonlocal correlations in an asymmetric quantum network

The nonlocality revealed in a multiparty multisource network Bell experiment is conceptually different than the standard multiparty Bell nonlocality involving a single common source. Here, by introducing variants of asymmetric bilocal as well as trilocal network scenarios, we go beyond the typical bilocal network scenario where both the edge parties have an equal number of measurement settings. We first introduce an asymmetric bilocal network where one of the edge parties (say, Alice) receives ${2}^{n\ensuremath{-}1}$ inputs and the other edge party (say, Charlie) receives $n$ inputs. We derive two variants of asymmetric bilocality inequalities and demonstrate their optimal quantum violations. Further, we explore two types of asymmetric trilocal scenarios: (i) when two edge parties receive ${2}^{n\ensuremath{-}1}$ inputs each and the other edge party receives $n$ inputs, and (ii) when one edge party receives ${2}^{n\ensuremath{-}1}$ inputs and the other two edge parties have $n$ inputs each. We use an elegant sum-of-squares technique that enables us to evaluate the quantum optimal values of the proposed network inequalities without assuming the dimension of the systems for both the asymmetric bilocal as well as the trilocal scenarios. Further, we demonstrate the robustness of the quantum violations of the proposed inequalities in the presence of white noise.

Exotics from QCD Sum Rules

Many new exotic states in the charmonium mass region were discovered in the last decades by BaBar, Belle, CLEO-c, CDF, DØ, BESIII, LHCb and CMS Collaborations. We use the QCD Sum Rule approach to study some of these states.

Recycling nonlocality in quantum star networks

The nonlocality of an entangled qubit pair can be recycled for several Bell experiments. Here, we go beyond standard Bell scenarios and investigate the recycling of nonlocal resources in a quantum network. First, we show that the ability to recycle nonlocality can be independent of the size of the network. Then, we realize a photonic quantum three-branch star network in which three sources of entangled pairs independently connect three outer parties with a central node. After measuring, each outer party respectively relays their system to an independent secondary measuring party. We experimentally demonstrate that the outer parties can perform unsharp measurements that are strong enough to violate a network Bell inequality with the central party, but weak enough to maintain sufficient entanglement in the network to allow the three secondary parties to do the same. Moreover, the violations are strong enough to exclude any model based on standard projective measurements on the Einstein-Podolsky-Rosen pairs emitted in the network. Our experiment brings together the research program of recycling quantum resources with that of Bell nonlocality in networks.

The branching fraction of {B}_s^0to {K}^0{overline{K}}^0 : three puzzles

The branching fraction of the {B}_sto {K}^0{overline{K}}^0 decay has been recently measured by the LHCb and Belle experiments. We study the consistency of the measured value with three relations to other decay rates and CP asymmetries which follow from the Standard Model, and from the approximate flavor SU(3) symmetry of the strong interactions. We find that each of these relations is violated at a level of above 3σ. We argue that various subleading effects — rescattering, electroweak penguins and SU(3) breaking — if larger than theoretically expected, can account for some of these puzzles, but not for all of them simultaneously.

Measurement of the branching fractions for Cabibbo-suppressed decays D+→K+K−π+π0 and D(s)+→K+π−π+π0 at Belle

We present measurements of the branching fractions for the singly Cabibbo-suppressed decays D+→K+K−π+π0 and Ds+→K+π−π+π0, and the doubly Cabibbo-suppressed decay D+→K+π−π+π0, based on 980 fb−1 of data recorded by the Belle experiment at the KEKB e+e− collider. We measure these modes relative to the Cabibbo-favored modes D+→K−π+π+π0 and Ds+→K+K−π+π0. Our results for the ratios of branching fractions are B(D+→K+K−π+π0)/B(D+→K−π+π+π0)=(11.32±0.13±0.26)%, B(D+→K+π−π+π0)/B(D+→K−π+π+π0)=(1.68±0.11±0.03)%, and B(Ds+→K+π−π+π0)/B(Ds+→K+K−π+π0)=(17.13±0.62±0.51)%, where the uncertainties are statistical and systematic, respectively. The second value corresponds to (5.83±0.42)×tan4θC, where θC is the Cabibbo angle; this value is larger than other measured ratios of branching fractions for a doubly Cabibbo-suppressed charm decay to a Cabibbo-favored decay. Multiplying these results by world average values for B(D+→K−π+π+π0) and B(Ds+→K+K−π+π0) yields B(D+→K+K−π+π0)=(7.08±0.08±0.16±0.20)×10−3, B(D+→K+π−π+π0)=(1.05±0.07±0.02±0.03)×10−3, and B(Ds+→K+π−π+π0)=(9.44±0.34±0.28±0.32)×10−3, where the third uncertainty is due to the branching fraction of the normalization mode. The first two results are consistent with, but more precise than, the current world averages. The last result is the first measurement of this branching fraction.Received 3 May 2022Accepted 28 September 2022DOI:https://doi.org/10.1103/PhysRevD.107.033003Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectroweak interactionPhysical SystemsCharmed mesonsTechniquesParticle decaysParticles & Fields

Sharing preparation contextuality in a Bell experiment by an arbitrary pair of sequential observers

Based on the quantum violation of the bipartite Bell inequality, it has been established that the sharing of nonlocality can be demonstrated for at most two sequential observers at one end and at most one pair of observers at both ends. In this work we study the sharing of nonlocality and preparation contextuality based on a bipartite Bell inequality, involving arbitrary $n$ measurements by one party and ${2}^{n\ensuremath{-}1}$ measurements by another party. Such a Bell inequality has two bounds, the local bound and the preparation noncontextual bound, which is smaller than the local bound. We show that while nonlocality can be shared only by the first pair of the sequential observers, the preparation contextuality can be shared by an arbitrary pair of independent sequential observers at both ends.

Measurement of two-photon decay width of χc2(1P) in γγ → χc2(1P) → J/ψγ at Belle

We report the measurement of the two-photon decay width of χc2(1P) in two-photon processes at the Belle experiment. We analyze the process γγ → χc2(1P) → J/ψγ, J/ψ → ℓ+ℓ− (ℓ = e or μ) using a data sample of 971 fb−1 collected with the Belle detector at the KEKB e+e− collider. In this analysis, the product of the two-photon decay width of χc2(1P) and the branching fraction is determined to be {Gamma}_{gamma gamma}left({chi}_{c2}(1P)right)mathcal{B}left({chi}_{c2}(1P)to J/psi gamma right)mathcal{B}left(J/psi to {ell}^{+}{ell}^{-}right)=14.8pm 0.3left(textrm{stat}.right)pm 0.7left(textrm{syst}.right) eV, which corresponds to Γγγ(χc2(1P)) = 653 ± 13(stat.) ± 31(syst.) ± 17(B.R.) eV, where the third uncertainty is from mathcal{B} (χc2(1P) → J/ψγ) and mathcal{B} (J/ψ → ℓ+ℓ−).

Understanding the nature of Ω(2012) in a coupled-channel approach

We perform a systematic analysis of the mass and strong decays of the $\mathrm{\ensuremath{\Omega}}(2012)$ resonance in a coupled-channel approach of a bare three-quark state and a composite meson-baryon state. Besides the coupling of the bare state and ${\mathrm{\ensuremath{\Xi}}}^{*}\overline{K}$ channel, the effective meson-baryon interactions are also included. We find a pole with a mass of 2008 MeV by solving the Bethe-Salpeter equation. The calculated decay widths and its ratios of branching fractions ${\mathcal{R}}_{\mathrm{\ensuremath{\Xi}}\overline{K}}^{\mathrm{\ensuremath{\Xi}}\ensuremath{\pi}\overline{K}}$ agree well with the new experimental measurement by the Belle Collaboration. Our results suggest that both three-quark core and ${\mathrm{\ensuremath{\Xi}}}^{*}\overline{K}$ channel are essential for the description of the $\mathrm{\ensuremath{\Omega}}(2012)$ resonance. We expect that present calculations can help us to better understand the nature of $\mathrm{\ensuremath{\Omega}}(2012)$ resonance.