arXiv subjects

Zhen-Xing Zhao

Publications and source records attributed to Zhen-Xing Zhao.

At least 19 recordsLinked to original sources

arXiv2026

From QCD sum rules to HQET sum rules: Heavy-quark limit of four-quark operator matrix elements

Heavy quark expansion theory provides the standard theoretical framework for understanding the lifetimes of weakly decaying heavy-flavor hadrons. Within this framework, the matrix elements of four-quark operators play a crucial role in explaining the lifetime differences among hadrons containing the same heavy quark. In this work, we calculate these matrix elements at leading order using full QCD sum rules, with particular emphasis on deriving the corresponding HQET sum rules by taking the heavy-quark limit. While this limit is straightforward for most contributions, it turns out to be rather nontrivial for certain ones. Numerical analyses show that the results obtained from the two approaches are consistent with each other. We further clarify the origin of the large discrepancies reported in the literature between full QCD sum rule and HQET sum rule results. This work contributes to a deeper understanding of the relationship between the two sum-rule approaches and is expected to facilitate future applications of QCD and HQET sum rules in the study of heavy-flavor hadrons. The findings presented here may be of interest to both practitioners of QCD sum rules and researchers working on effective field theories.

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arXiv2025

Semileptonic $s\to u$ decays of singly heavy baryons

$s\to u$ weak decays of heavy flavor hadrons play a unique role in the field of heavy flavor physics. In this work, we investigate semileptonic $s\to u$ decays of singly heavy baryons in the light-front approach under the three-quark picture. Firstly, we provide all the form factors using this quark model, especially for $f_{3}$ and $g_{3}$, which are usually considered non-extractable in recent literature. We also discuss the heavy quark limit for the form factors, and some of our results differ from those in the literature. We find that, when considering the heavy quark limit, the $m_{s}$ correction may not be negligible. Secondly, we apply the obtained form factors to predict some observables in semileptonic decays. It is worth noting that, due to the extremely small phase space, lepton flavor universality (LFU) is sensitive to the masses of leptons, and precise measurement of LFU is expected to be an important tool for testing the standard model.

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arXiv2025

Weak decays of singly heavy baryons: the $1/2\to3/2$ case

This work is devoted to investigating the $1/2\to3/2$ weak decays of singly heavy baryons. Due to the orthogonality between the spin wavefunctions of antitriplet baryons and spin-3/2 baryons, the weak decay amplitude for such processes vanishes at the leading order of QCD. Consequently, this study exclusively examines the weak decays of $Ω_{Q}$. Using the light-front approach under the three-quark picture, we first extract the relevant form factors, and then apply them to investigate corresponding semileptonic and nonleptonic decays. Finally, we compare our phenomenological predictions with existing results in the literature. Our findings are expected to be helpful in experimentally establishing these decay channels.

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arXiv2025

Semileptonic and nonleptonic $\bar{B}_{s}\to D_{sJ}$ decays in covariant light-front approach

In this work, we investigate the $\bar{B}_{s}\to D_{sJ}$ transitions in covariant light-front approach, where $D_{sJ}$ denotes an s-wave or p-wave $c\bar{s}$ meson state. We first obtain the transition form factors within the framework of the quark model, and then apply the obtained form factors to obtain the branching fractions of semileptonic and nonleptonic decays. We also compare our results with experimental data and other theoretical predictions. We find that some branching fractions are sizable and might be accessible at the LHC and future $e^{+}$-$e^{-}$ colliders. Our work is expected to be of great value for establishing corresponding decay channels, and also be helpful in understanding the non-perturbative QCD dynamics.

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arXiv2024

Implications on CP violation of charmless three body decays of bottom baryon from the U-spin analysis

Motivated by recent LHCb measurements of CP violation in $Λ_b$ three-body decays, we conduct an analysis of CP asymmetry in three-body decays of bottom baryons utilizing U-spin symmetry. We first develop a convenient representation that facilitates the incorporation of U-spin symmetry into our analysis. By integrating weak and strong phases into the derived amplitude, we obtain the CP asymmetry and establish relationships between CP asymmetries in U-spin related decay channels. With the help of experimental measurements, we provide numerical predictions for the CP asymmetries for other decay channels, particularly $Λ_b \to Σ^0 K^+ K^-$, $Ξ^0_b \to Λπ^+ π^-$, $Λ_b \to Σ^0 K^+ π^-$, and $Ξ^0_b \to ΣK^- π^+$. Furthermore, we provide a quantity that can be used as a null test of standard model and deviations from 0 will reflect the possible new physics. These results are valuable for CPV measurements in baryon decays, and can be tested in future experiments.

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arXiv2024

Weak decays of triply heavy baryons in the light-front approach

In this work, we investigate the weak decays of ground-state triply heavy baryons. We first obtain the form factors using the light-front quark model in the three-quark picture, and then apply them to arrive at some phenomenological predictions, including the decay widths of semileptonic decays and nonleptonic decays. Our results are expected to be helpful for the experimental search for triply heavy baryons.

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arXiv2024

Light-cone sum rules study on the purely non-factorizable $Λ_{c}^{+}\toΞ^{0}K^{+}$ decay

We investigate the purely non-factorizable $Λ_{c}^{+}\toΞ^{0}K^{+}$ decay using light-cone sum rules. To extract the decay amplitudes, a three-point correlation function is defined and calculated at hadron and quark-gluon level, respectively. Both the W-exchange and the W-inward emission diagrams are considered in the quark-gluon level calculation, where the two-particle light-cone distribution amplitudes (LCDAs) of kaon are used as non-perturbative input. We obtain the decay amplitudes contributed from the twist-2 and twist-3 kaon LCDAs, respectively. The obtained P-wave amplitude is consistent with those predicted in the literature, while the S-wave one is much smaller. This significant difference between the S- and P- wave amplitudes leads to small up-down spin asymmetry, closing to the experimental measurement.

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arXiv2024

A progress in inverse matrix method in QCD sum rules

In traditional QCD sum rules, the simple hadron spectral density model of ``delta-function-type ground state + theta-function-type continuous spectrum" determines that there is no perfect parameter selection. In recent years, inverse problem methods, especially the inverse matrix method, have shown better handling of QCD sum rules. This work continues to develop the inverse matrix method. Considering that the narrow-width approximation may still be a good approximation, we separate the contribution of the ground state from the spectral density. Then follow the general steps of the inverse matrix method to extract physical quantities such as decay constants that we are sometimes more interested in.

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arXiv2024

Light baryon in three quark picture light front approach and its application: hyperon weak radiative decays

Motivated by recent experimental data on $Σ^+\to pγ$ at BESIII, we investigate a class of hyperon weak radiative decays. To estimate these processes, in our research, we employ a new type of light-front quark model with a three-quark picture for octet baryons. In the three-quark picture, with the use of $SU(3)_f$ and spin symmetries, we present a general form of the light front wave function for each octet baryon. By including contributions from the penguin diagram and W exchange diagram, we perform a complete calculation on the branching ratios ($Br$) and the asymmetry parameter ($α$) for hyperon weak radiative decay processes. Our results are helpful for discovering additional hyperon weak radiative decay processes in experimental facilities, and our research will promote the theoretical study of baryons.

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arXiv2023

On the four-quark operator matrix elements for the lifetime of $Λ_{b}$

Heavy quark expansion can nicely explain the lifetime of $Λ_{b}$. However, there still exist sizable uncertainties from the four-quark operator matrix elements of $Λ_{b}$ in $1/m_{b}^{3}$ corrections, which describe the spectator effects. In this work, these four-quark operator matrix elements are investigated using full QCD sum rules for the first time. At the QCD level, contributions from up to dimension-6 four-quark operators are considered. Our method of calculating high-dimensional operator matrix elements is promising to be used to resolve the $Ω_{c}$ lifetime puzzle.

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arXiv2023

Semi-leptonic form factors of $Ξ_{c}\toΞ$ in QCD sum rules

There exists a significant deviation between the most recent Lattice QCD simulation and experimental measurement by Belle for $Ξ_{c}^{0}\toΞ^{-}\ell^{+}ν_{\ell}$. In this work, we investigate the $Ξ_{c}\toΞ$ form factors in QCD sum rules. To this end, the two-point correlation functions of $Ξ_{c}$ and $Ξ$, and the three-point correlation functions of $Ξ_{c}\toΞ$ are calculated. At the QCD level, contributions from up to dimension-6 four-quark operators are considered, and the leading order results of the Wilson coefficients are obtained. For the form factors, relatively stable Borel windows can be found. Our form factors are comparable with those of Lattice QCD, except for $f_{\perp}$. The obtained form factors are then used to predict the branching ratios of $Ξ_{c}\toΞ\ell^{+}ν_{\ell}$, and our predictions are consistent with the most recent data of ALICE and Belle, and those of Lattice QCD within error. Given that the branching ratios only contain limited information, we suggest the experimentalists directly measure the form factors of $Ξ_{c}\toΞ$.

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arXiv2023

Revisiting $Ξ_{Q}-Ξ_{Q}^{\prime}$ mixing in QCD sum rules

In this work, we perform a QCD sum rules analysis on the $Ξ_{Q}-Ξ_{Q}^{\prime}$ mixing. Contributions from up to dimension-6 four-quark operators are considered. However, it turns out that, only dimension-4 and dimension-5 operators contribute, which reveals the non-perturbative nature of mixing. Especially we notice that only the diagrams with the two light quarks participating in gluon exchange contribute to the mixing. Our results indicate that the mixing angle $θ_{c}=(1.2\sim2.8)^{\circ}$ for the $Q=c$ case and $θ_{b}=(0.28\sim0.34)^{\circ}$ for the $Q=b$ case. Our prediction of $θ_{c}$ is consistent with the most recent Lattice QCD result within error. Such a small mixing angle seems unlikely to resolve the tension between the recent experimental measurement from Belle and Lattice QCD calculation for the semileptonic decay $Ξ_{c}^{0}\toΞ^{-} e^{+}ν_{e}$.

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arXiv2023

Baryons in the light-front approach: The three-quark picture

In this work, a three-quark picture is constructed using a bottom-up approach for baryons in light-front quark model. The shape parameters, which characterize the momentum distribution inside a baryon, are determined with the help of the pole residue of the baryon. The relation between the three-quark picture and the diquark picture is clarified. When building the model, we find that Lorentz boost plays a crucial role, and the bottom-up modeling approach can be generalized to multiquark states. Based on this, a unified theoretical framework for describing multiquark states may be established. As a by-product of model construction, we can easily obtain a newly improved definition of baryon interpolating current. The hadron interpolating currents are the starting point of Lattice QCD and QCD sum rules, and therefore are of great importance.

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arXiv2023

Analysis of the interpolating currents of baryons: anomalous dimension

The anomalous dimensions for the interpolating currents of baryons are indispensable inputs in a serious QCD analysis of baryon. However, the results in the literature are vague. In view of this, in this work, we investigate the one-loop anomalous dimensions for some interpolating currents such as those of $Λ_{Q}$ and proton. Under the requirement of precise testing the Standard Model, this study is essential and significant for the QCD analysis in the future.

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arXiv2022

W-exchange contribution to the decays $Ξ_{cc}^{++}\toΞ_{c}^{+(\prime)}π^{+}$ using light-cone sum rules

We calculate the W-exchange contribution to the $Ξ_{cc}^{++}\toΞ_{c}^{+(\prime)}π^{+}$ decay using light-cone sum rules. The two-particle light-cone distribution amplitudes of the pion are used as non-perturbative input for the sum rules calculation, and the perturbative kernel is calculated at the leading order. We obtain the corresponding decay branching fractions by combining our W-exchange amplitudes with the factorizable amplitudes given by various theoretical methods from the literature. It is shown that with the factorizable amplitudes from heavy quark effective theory, we obtain the branching fraction ratio ${\cal B}(Ξ_{cc}^{++}\toΞ_{c}^{+\prime}π^{+})/{\cal B}(Ξ_{cc}^{++}\toΞ_{c}^{+}π^{+})= 1.42\pm 0.78$, which is consistent with the experimental value of $1.41\pm 0.17\pm 0.1$.

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arXiv2021

QCD sum rules analysis of weak decays of doubly heavy baryons: the $b\to c$ processes

A comprehensive study of $b\to c$ weak decays of doubly heavy baryons is presented in this paper. The transition form factors as well as the pole residues of the initial and final states are respectively obtained by investigating the three-point and two-point correlation functions in QCD sum rules. Contributions from up to dimension-6 operators are respectively considered for the two-point and three-point correlation functions. The obtained form factors are then applied to a phenomenological analysis of semi-leptonic decays.

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arXiv2021

Resonance contributions in $B^-\to K^+K^-π^-$ within the light-come sum rule approach

In this work, we study the resonance contributions to the decay $B^-\to K^+K^-π^-$, which is dominated by the scalar $f_0(980), K_0^*(1430)$, vector $ρ(1450), ϕ(1020), K^*(892)$ and tensor $f_2(1270)$ resonances. The three-body decay is reduced to various quasi two-body decays, where the $B$ meson firstly decays into a resonance and a pion or a kaon, subsequently the resonance decays into the other two final-state mesons. The quasi two-body decays are calculated within the light-cone sum rule approach utilizing the leading twist $B$ meson light-cone distribution amplitudes. Finally, the decay branching fraction contribution from each resonance are calculated. Some of them are compatible with experiment or previous theoretical works. Including the effects of non-resonant and final-state interactions, we also evaluate the total branching fraction.

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arXiv2020

SU(3) analysis of fully-light tetraquarks in heavy meson weak decays

We perform a SU(3) analysis for both semi-leptonic and non-leptonic heavy meson weak decays into a pseudoscalar meson and a fully-light tetraquark in 10 or 27 representation. A reduction of the SU(3) representation tensor for the fully-light tetraquarks is produced and all the flavor components for each representation tensor are listed. The decay channels we analysis include $B/D \to U/T~P~lν$, $B/D \to U/T~P $ and $B_c \to U/T~P/D$, with $U/T$ represents a fully-light tetraquark in 10 or 27 representation and $P$ is a pseudoscalar meson. Finally, among these results we list all the golden decay channels which are expected to have more possibilities to be observed in experiments.

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