Belle Experiment Research Articles

Measurements of the branching fractions B(B¯0→D*+π−) and B(B¯0→D*+K−) and tests of QCD factorization

Using (771.6±10.6)×106 BB¯ meson pairs recorded by the Belle experiment at the KEKB e+e− collider, we report the branching fractions B(B¯0→D*+π−)=(2.62±0.02±0.09)×10−3 and B(B¯0→D*+K−)=(2.22±0.06±0.08)×10−4; the quoted uncertainties are statistical and systematic, respectively. A measurement of the ratio of these branching fractions is also presented, RK/π=B(B¯→D*+K−)/B(B¯→D*+π−)=(8.41±0.24±0.13)×10−2, where systematic uncertainties due to the D*+ meson reconstruction cancel out. Furthermore, we report a new QCD factorization test based on the measured ratios for B¯→D*+h− and B¯→D*+ℓ−ν decays at squared momentum transfer values equivalent to the mass of the h=π or K hadron. The parameters |a1(h)| are measured to be |a1(π)|=0.884±0.004±0.003±0.016 and |a1(K)|=0.913±0.019±0.008±0.013, where the last uncertainties account for all external inputs. These values are approximately 15% lower than those expected from theoretical predictions. Subsequently, flavor SU(3) symmetry is tested by measuring the ratios for pions and kaons, |a1(K)|2/|a1(π)|2=1.066±0.042±0.018±0.023, as well as for different particle species. The ratio is consistent with unity and therefore no evidence for SU(3) symmetry breaking effects is found at the 5% precision level.Received 3 July 2022Accepted 10 October 2022DOI:https://doi.org/10.1103/PhysRevD.107.012003Published 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 fractionPhysical SystemsBottom mesonsParticles & Fields

Extending the fair sampling assumption using causal diagrams

Discarding undesirable measurement results in Bell experiments opens the detection loophole that prevents a conclusive demonstration of nonlocality. As closing the detection loophole represents a major technical challenge for many practical Bell experiments, it is customary to assume the so-called fair sampling assumption (FSA) that, in its original form, states that the collectively postselected statistics are a fair sample of the ideal statistics. Here, we analyze the FSA from the viewpoint of causal inference: We derive a causal structure that must be present in any causal model that faithfully encapsulates the FSA. This provides an easy, intuitive, and unifying approach that includes different accepted forms of the FSA and underlines what is really assumed when using the FSA. We then show that the FSA can not only be applied in scenarios with non-ideal detectors or transmission losses, but also in ideal experiments where only parts of the correlations are postselected, e.g., when the particles' destinations are in a superposition state. Finally, we demonstrate that the FSA is also applicable in multipartite scenarios that test for (genuine) multipartite nonlocality.

B → K(∗)νν̄ in covariant confined quark model

We study the [Formula: see text] decays within the Standard Model (SM) by using the relevant transition form factors obtained from the covariant confined quark model (CCQM) developed by us. The [Formula: see text] and [Formula: see text] transition form factors are calculated in the full kinematic [Formula: see text] range. The branching fractions are then calculated. It is shown that our results are in an agreement with those obtained in other theoretical approaches. Currently, the BaBar and Belle collaborations provide us by the upper limits at 90% confidence limit. The obtained bounds are roughly an order of magnitude larger than the SM predictions. This should stimulate experimental collaborations to set up experiments that allow one to obtain more accurate branching values, which is quite achievable on the updated LHCb and Belle machines. If the discrepancies between theory and experiment are confirmed, this will open up opportunities for constructing models with new particles and interactions leading to an extension of the SM.

Why Bell's Experiment Is Meaningless

Why Bell's Experiment Is Meaningless

The Bell Inequality, Inviolable by Data Used Consistently with Its Derivation, Is Satisfied by Quantum Correlations Whose Probabilities Satisfy the Wigner Inequality

It is not generally known that the inequality that Bell derived using three random variables must be identically satisfied by any three corresponding data sets of ±1’s that are writable on paper. This surprising fact is not immediately obvious from Bell’s inequality derivation based on causal random variables, but follows immediately if the same mathematical operations are applied to finite data sets. For laboratory data, the inequality is identically satisfied as a fact of pure algebra, and its satisfaction is independent of whether the processes generating the data are local, non-local, deterministic, random, or nonsensical. It follows that if predicted correlations violate the inequality, they represent no three cross-correlated data sets that can exist, or can be generated from valid probability models. Reported data that violate the inequality consist of probabilistically independent data-pairs and are thus inconsistent with inequality derivation. In the case of random variables as Bell assumed, the correlations in the inequality may be expressed in terms of the probabilities that give rise to them. A new inequality is then produced: The Wigner inequality, that must be satisfied by quantum mechanical probabilities in the case of Bell experiments. If that were not the case, predicted quantum probabilities and correlations would be inconsistent with basic algebra.

Recent Measurements of Decay Asymmetry Parameter and CP Asymmetry for Charmed Baryon Decays at Belle

We review the recent results from the Belle experiment on the measurements of branching fractions and decay asymmetry parameters (α) for the hadronic weak decays of charmed baryons, including Λc+→B+P: Λc+→(Λ,Σ0)h+ (h=π,K) and Λc+→Σ+(π0,η,η′); Ξc0→B+P: Ξc0→Ξ−π+; Ξc0→B+V: Ξc0→ΛK¯*0, Ξc0→Σ0K¯*0, and Ξc0→Σ+K*−. In addition, we present an overview of the searches for CP violation via the α-induced CP asymmetry for Λc+→(Λ,Σ0)h+ and Ξc0→Ξ−π+. Finally, we discuss the promising decay modes of Ωc0 which can be measured in the near future and are indispensable in searching for CP violation in the charm sector.

Production of loosely bound hadron molecules from bottomonium decays

We present multiple results on the production of loosely bound molecules in bottomonium annihilations and ${e}^{+}{e}^{\ensuremath{-}}$ collisions at $\sqrt{s}=10.58\text{ }\text{ }\mathrm{GeV}$. We perform the first comprehensive test of several models for deuteron production against all the existing data in this energy region. We fit the free parameters of the models to reproduce the observed cross sections, and we predict the deuteron spectrum and production and the cross section for the ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}d\overline{d}+X$ process both at the $\mathrm{\ensuremath{\Upsilon}}(1,2,3S)$ resonances and at $\sqrt{s}=10.58\text{ }\text{ }\mathrm{GeV}$. The predicted spectra show differences but are all compatible with the uncertainties of the existing data. These differences could be addressed if larger datasets are collected by the Belle II experiment. Fixing the source size parameter to reproduce the deuteron data, we then predict the production rates for $H$ dibaryon and hypertriton in this energy region using a simple coalescence model. Our prediction on the $H$ dibaryon production rate is below the limits set by the direct search at the Belle experiment, but in the range accessible to the Belle II experiment. The systematic effect due to the MC modeling of quarks and gluon fragmentation into baryons is reduced, deriving a new tuning of the pythia 8 Monte Carlo generator using the available measurement of single- and double-particle spectra in $\mathrm{\ensuremath{\Upsilon}}$ decays.

Exponentially Decreasing Critical Detection Efficiency for Any Bell Inequality.

We address the problem of closing the detection efficiency loophole in Bell experiments, which is crucial for real-world applications. Every Bell inequality has a critical detection efficiency η that must be surpassed to avoid the detection loophole. Here, we propose a general method for reducing the critical detection efficiency of any Bell inequality to arbitrary low values. This is accomplished by entangling two particles in N orthogonal subspaces (e.g., N degrees of freedom) and conducting N Bell tests in parallel. Furthermore, the proposed method is based on the introduction of penalized N-product (PNP) Bell inequalities, for which the so-called simultaneous measurement loophole is closed, and the maximum value for local hidden-variable theories is simply the Nth power of the one of the Bell inequality initially considered. We show that, for the PNP Bell inequalities, the critical detection efficiency decays exponentially with N. The strength of our method is illustrated with a detailed study of the PNP Bell inequalities resulting from the Clauser-Horne-Shimony-Holt inequality.

Belle II status and prospect

The Belle II experiment at the SuperKEKB accelerator is the upgraded successor of one of the original B factories, the Belle experiment and KEKB accelerator. The instantaneous luminosity is designed to reach 6.5×1035cm−2s−1, which is 30 times higher than KEKB. We aim to accumulate 50ab−1 of the data by the early 2030s to discover new physics beyond the Standard Model. The current integrated luminosity has so far reached 213fb−1 by summer 2021. Belle II can also study various physics subjects: beauty, charm, τ-lepton, dark sector and hadron physics. We confirm the detector performance is as expected. Several physics results have already appeared. We briefly report the status and prospects of the Belle II experiment.

The possibility of X(4014) as a D^*{bar{D}}^* molecular state

Within the framework of the local hidden gauge approach, we have studied the near-threshold D^* {bar{D}}^* interaction with quantum numbers I(J^{PC}) = 0(0^{++}), 0(2^{++}), 1(0^{++}), and 1(2^{++}), respectively. The contact term and vector meson exchange term in coupled channels are taken into account in this work. One pole, which is found in the case of the quantum numbers I(J^{PC}) = 0(0^{++}), could be associated to the X(4014) recently observed by the Belle Collaboration. Thus, we suggest that the X(4014) may be an D^* {bar{D}}^* molecular state with I(J^{PC}) = 0(0^{++}), and more precise information about X(4014), such as resonance parameters and decay properties, could be useful to shed light on its structure.

Double-heavy tetraquarks with strangeness in the chiral quark model* *Supported partly by Natural Science Foundation of Jiangsu Province, China (BK20221166), and the National Natural Science Foundation of China (12205125, 847145, 12205249, 1865019)

Recently, some progress has been made in the experiments on double-heavy tetraquarks, such as reported by the LHCb Collaboration and reported by the Belle Collaboration. Coming on the heels of our previous work about and , we present a study on the bound and resonance states of their companions, () tetraquarks with strange flavor in the chiral quark model. Two pictures, meson-meson and diquark-antidiquark ones, and their couplings were considered in our calculations. Isospin violation was neglected herein. Our numerical analysis indicated that the states with and with are the most promising stable states against strong interactions. Besides, we found several resonance states for the double-heavy strange tetraquarks with the real scaling method.

Transverse momentum dependent fragmentation functions from recent BELLE data

A new formalism for the factorization of the cross section for single hadron production in $e^+e^-$ annihilations, differential in $z_h$, $P_T$ and thrust, is applied to the phenomenological analysis of data recently measured by the BELLE Collaboration. Within this scheme the $e^+e^- \to hX$ cross section can be recast in the convolution of a perturbatively calculable coefficient and a universal transverse momentum dependent fragmentation function. While performing a next-to-leading order calculation of the perturbative part of the process to next-to-leading logarithmic accuracy, we examine and thoroughly discuss the suitability of a number of possible ansatz to model the non-perturbative part of this universal transverse momentum dependent fragmentation function, showing the extent to which present experimental data can actually constrain its shape and functional form in terms of $z_h$, $P_T$ and thrust.

Interpretation of the Lambda _c(2910)^+ baryon newly seen by Belle Collaboration and its possible bottom partner

The developments in the experimental facilities and analyses techniques have recently lead to the observation of many hadronic states ranging from excitations of conventional hadrons to various exotic states. The baryons with single heavy quark are among these states providing an attractive field of research to get a better understanding of the nonperturbative nature of the strong interaction. Recently, the Belle Collaboration announced observation of the state Lambda _c(2910)^+ with a mass 2913.8pm 5.6pm 3.8~textrm{MeV}/c^2 and width 51.8pm 20.0pm 18.8~textrm{MeV}. In the present study, by the mass analyses of different excitations at Lambda _c channel and their comparison with existing experimental information, we find that the spin-parity of this newly found excited state is J^P= frac{1}{2}^- and it is a 2P state denoting by Lambda _c(frac{1}{2}^-,2P). We predict its current coupling as well, which can be served as one of the main input parameters to investigate different decays and interactions of this particle. We also determine the mass and current coupling of Lambda _b(frac{1}{2}^-,2P) as possible bottom counterpart of the new Lambda _c(2910)^+ state, which may be in agenda of different experiments in near future.

Analysis of Ω(2012) as a molecule in the chiral quark model

Inspired by the updated information on $\Omega(2012)$ by the Belle Collaboration, we conduct a study of all possible $S$-wave pentaquark systems with quark contents $sssq\bar{q},q=u,d$ in a chiral quark model with the help of Gaussian expansion method. Channel coupling is also considered. The real-scaling method (stabilization method) is employed to identify and check the bound states and the genuine resonances. In addition, the decay widths of all resonances are given. The results show that $\Omega(2012)$ can be interpreted as a $\Xi^*K$ molecular state with quantum number of $IJ^P=0(\frac{3}{2})^-$. Other resonances are obtained: $\Xi^* K^*$ with $IJ^P=0(\frac{1}{2})^-$ and$0(\frac{3}{2})^-$, $\Omega\pi$ with $IJ^P=1(\frac{3}{2})^-$. These pentaquark states is expected to be further verified in future experiments.

Higher-Order QCD Corrections to ϒ Decay into Double Charmonia

In this Letter, we study the exclusive decay of ϒ into J/ψ in association with η_{c} (χ_{c0,1,2}). The decay widths for different helicity configurations are evaluated up to QCD next-to-leading order within the nonrelativistic QCD framework. We find that the QCD corrections notably mitigate the renormalization scale dependence of the decay widths for all the processes. The branching fraction of ϒ→J/ψ+χ_{c1} is obtained as 3.73_{-2.06-1.19}^{+5.10+0.10}×10^{-6}, which agrees well with the Belle measurement, i.e., Br(ϒ→J/ψ+χ_{c1})=(3.90±1.21±0.23)×10^{-6}. For the other processes, our results of the branching fractions are compatible with the upper limits given by the Belle experiments, except for ϒ(2S)→J/ψ+χ_{c1}, where some tension exists between theory and experiment. Having the polarized decay widths, we study the J/ψ polarization, which turns out to be independent of any nonperturbative parameters. Further, according to our calculation, it is promising to measure all the processes at Super B factory thanks to the high luminosity.

Exclusive semileptonic B_c-meson decays to radially excited charmonium and charm meson states

In the wake of recent measurements of ratios of semileptonic branching fractions: {mathscr {R}}_{J/psi }, {mathscr {R}}_D and {mathscr {R}}_{D^{*}} reported by the LHCb, BELLE and HFLAV Collaborations, we calculate invariant form factors for the exclusive semileptonic B_c-meson decays to radially excited charmonium and charm meson states in the full kinematical region within the framework of relativistic independent quark (RIQ) model. We evaluate the lepton mass effect in the decay processes induced by brightarrow c,u transition at the quark level. Our predictions on branching fractions for B_crightarrow eta _c/psi (nS) are found sim 10^{-2}-10^{-4} and that for B_crightarrow D^{*}(nS) are sim 10^{-4} in their e^{-} decay modes, which lie within the detection accuracy of current experiment. Our predictions on branching fractions, forward backward asymmetry and asymmetry parameter are found in reasonable agreement with other model predictions; which can hopefully be tested in future experiments at LHC and Tevatron. Our predicted observable {mathscr {R}} in this sector are found comparable to other standard model (SM) predictions that violate the lepton flavor universality hinting at new physics beyond SM.

Naturally restricted subsets of nonsignaling correlations: typicality and convergence

It is well-known that in a Bell experiment, the observed correlation between measurement outcomes – as predicted by quantum theory – can be stronger than that allowed by local causality, yet not fully constrained by the principle of relativistic causality. In practice, the characterization of the set Q of quantum correlations is carried out, often, through a converging hierarchy of outer approximations. On the other hand, some subsets of Q arising from additional constraints [e.g., originating from quantum states having positive-partial-transposition (PPT) or being finite-dimensional maximally entangled (MES)] turn out to be also amenable to similar numerical characterizations. How, then, at a quantitative level, are all these naturally restricted subsets of nonsignaling correlations different? Here, we consider several bipartite Bell scenarios and numerically estimate their volume relative to that of the set of nonsignaling correlations. Within the number of cases investigated, we have observed that (1) for a given number of inputs ns (outputs no), the relative volume of both the Bell-local set and the quantum set increases (decreases) rapidly with increasing no (ns) (2) although the so-called macroscopically local set Q1 may approximate Q well in the two-input scenarios, it can be a very poor approximation of the quantum set when ns>no (3) the almost-quantum set Q~1 is an exceptionally-good approximation to the quantum set (4) the difference between Q and the set of correlations originating from MES is most significant when no=2, whereas (5) the difference between the Bell-local set and the PPT set generally becomes more significant with increasing no. This last comparison, in particular, allows us to identify Bell scenarios where there is little hope of realizing the Bell violation by PPT states and those that deserve further exploration.

$\Lambda$ Polarizing Fragmentation Function from Belle $e^+ e^-$ data

Experimental data from Belle Collaboration for the transverse polarization of \LambdaΛ’s measured in e^+ e^-e+e− annihilation processes are used to extract the polarizing fragmentation function (FF) within a TMD approach. We consider both associated and inclusive \LambdaΛ production, showing a quite consistent scenario. Good separation in flavor is obtained, leading to four independent FFs. Predictions for SIDIS processes at the EIC, crucial for understanding their universality and evolution properties, are also presented.

Search for Z′→μ+μ− in the Lμ−Lτ gauge-symmetric model at Belle

We search for a new gauge boson $Z'$ that couples only to heavy leptons and their corresponding neutrinos in the process $e^{+} e^{-} \rightarrow Z'(\rightarrow \mu^{+}\mu^{-}) \mu^{+}\mu^{-}$, using a 643 fb$^{-1}$ data sample collected by the Belle experiment at or near the $\Upsilon(1S,2S,3S,4S,5S)$ resonances at the KEKB collider. For the first time, effects due to initial state radiation are used in estimating the detection efficiency. No signal is observed in the mass range of 0.212 \ -- 10 GeV/${\it c}^2$ and we set an upper limit on the coupling strengh, $g'$, constraining $Z'$ as a possible contributor to the anomalous magnetic dipole moment of muon.

The pseudoscalar meson and baryon octet interaction with strangeness S = −2 in the unitary coupled-channel approximation

The interaction of the pseudoscalar meson and the baryon octet with strangeness and isospin is investigated by solving the Bethe–Salpeter equation in the infinite and finite volume respectively. It is found that there is a resonance state generated dynamically, which owns a mass of about 1550 MeV and a large decay width of 120–200 MeV. This resonance state couples strongly to the π channel. Therefore, it might not correspond to the particle announced by Belle collaboration. At the same time, this problem is studied in the finite volume, and an energy level at 1570 MeV is obtained, which is between the and thresholds and independent of the cubic box size.