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Zhu-Feng Zhang

Publications and source records attributed to Zhu-Feng Zhang.

13 recordsLinked to original sources

Possible Bound States in the $D^\ast\bar D^\ast$/$B^\ast\bar B^\ast$ and $D^\ast D^\ast$/$\bar B^\ast\bar B^\ast$ Systems within the Bethe-Salpeter Formalism

We investigate possible $S$-wave bound states in the $D^\ast\bar D^\ast$, $B^\ast\bar B^\ast$, $D^\ast D^\ast$, and $\bar B^\ast\bar B^\ast$ systems within the Bethe-Salpeter formalism using one-boson-exchange interactions. Bound state solutions are obtained in the isoscalar hidden-heavy systems with $J^{PC}=0^{++}$, $1^{+-}$, and $2^{++}$, whereas no isovector solutions are found within the parameter range considered. For the doubly heavy systems, solutions are obtained in the allowed $I(J^P)=0(1^+)$, $1(0^+)$, and $1(2^+)$ systems, although the $1(0^+)$ solution requires a comparatively large cutoff parameter. The bottom systems are bounded more favorably than their charmed counterparts because of their larger reduced masses.

hep-ph

The properties of the $S$-wave $D_s\bar{D}_s$ bound state

In this work, we investigate possible bound states of the $D_s\bar{D}_s$ system in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. By numerically solving the Bethe-Salpeter equation with a kernel that includes the contributions from $ϕ$ and $J/ψ$ exchanges, we confirm the existence of a bound state in the $D_s\bar{D}_s$ system. We further investigate the partial decay widths of the $D_s\bar{D}_s$ bound state into $D\bar{D}$, $η_cη$, and $J/ψω$, finding that these partial widths are sensitive to the parameter $α$ in our model. Notably, we observe that the dominant decay channel for the $D_s\bar{D}_s$ bound state is that into $D\bar{D}$.

hep-ph

Investigating $S$-wave bound states composed of two pseudoscalar mesons

In this work, we systematically investigate the two-pseudoscalar meson systems with the Bethe-Salpeter equation in the ladder and instantaneous approximations. By solving the Bethe-Salpeter equation numerically with the kernel containing the one-particle exchange diagrams, we find that the $K\bar{K}$, $DK$, $B\bar{K}$, $D\bar{D}$, $B\bar{B}$, $BD$, $D\bar{K}$, $BK$, and $B\bar{D}$ systems with $I=0$ can exist as bound states. We also study the contributions from heavy meson ($J/ψ$ and $Υ$) exchanges, and we find that the contribution from heavy meson exchange can not be ignored.

hep-ph

Mixing of X and Y states from QCD Sum Rules analysis

We study $\bar{Q}Q\bar{q}q$ and $\bar{Q}qQ\bar{q}$ states as mixed states in QCD sum rules. By calculating the two-point correlation functions of pure states of their corresponding currents, we review the mass and coupling constant predictions of $J^{PC}=1^{++}$, $1^{--}$, $1^{-+}$ states. By calculating the two-point mixed correlation functions of $\bar{Q}Q\bar{q}q$ and $\bar{Q}qQ\bar{q}$ currents, and we estimate the mass and coupling constants of the corresponding `"physical state" that couples to both $\bar{Q}Q\bar{q}q$ and $\bar{Q}qQ\bar{q}$ currents. Our results suggest that $1^{++}$ states are more likely mixing from $\bar{Q}Q\bar{q}q$ and $\bar{Q}qQ\bar{q}$ components, while for $1^{--}$ and $1^{-+}$ states, there is less mixing between $\bar{Q}Q\bar{q}q$ and $\bar{Q}qQ\bar{q}$. Our results suggest the $Y$ series of states have more complicated components.

hep-ph

Studying the $\bar{D}_1K$ molecule in the Bethe-Salpeter equation approach

We interpret the $X_1(2900)$ as an $S$-wave $\bar{D}_1K$ molecular state in the Bethe-Salpeter equation approach with the ladder and instantaneous approximations for the kernel. By solving the Bethe-Salpeter equation numerically with the kernel containing one-particle-exchange diagrams and introducing three different form factors (monopole, dipole, and exponential form factors) in the verties, we find the bound state exists. We also study the decay width of the decay $X_1(2900)$ to $D^-K^+$.

hep-ph

Phenomenological studies on the $\bar{B}^0\rightarrow [K^-π^+]_{S/V}[π^+π^-]_{V/S} \rightarrow K^-π^+π^+π^-$ decay

Within the quasi-two-body decay model, we study the localized $CP$ violation and branching fraction of the four-body decay $\bar{B}^0\rightarrow [K^-π^+]_{S/V}[π^+π^-]_{V/S} \rightarrow K^-π^+π^-π^+$ when $K^-π^+$ and $π^-π^+$ pair invariant masses are $0.35<m_{K^-π^+}<2.04 \, \mathrm{GeV}$ and $0<m_{π^-π^+}<1.06\, \mathrm{GeV}$, with the pairs being dominated by the $\bar{K}^*_0(700)^0$, $\bar{K}^*(892)^0$, $\bar{K}^*(1410)^0$, $\bar{K}^*_0(1430)$ and $\bar{K}^*(1680)^0$, and $f_0(500)$, $ρ^0(770)$ , $ω(782)$ and $f_0(980)$ resonances, respectively. When dealing with the dynamical functions of these resonances, $f_0(500)$, $ρ^0(770)$, $f_0(980)$ and $\bar{K}^*_0(1430)$ are modeled with the Bugg model, Gounaris-Sakurai function, Flatt$\acute{\mathrm{e}}$ formalism and LASS lineshape, respectively, while others are described by the relativistic Breit-Wigner function. Adopting the end point divergence parameters $ρ_A\in[0,0.5]$ and $ϕ_A\in[0,2π]$, our predicted results are $\mathcal{A_{CP}}(\bar{B}^0\rightarrow K^-π^+π^+π^-)\in[-0.383,0.421]$ and $\mathcal{B}(\bar{B}^0\rightarrow K^-π^+π^+π^-)\in[7.36,199.69]\times10^{-8}$ based on the hypothetical $q\bar{q}$ structures for the scalar mesons in the QCD factorization approach. Meanwhile, we calculate the $CP$ violating asymmetries and branching fractions of the two-body decays $\bar{B}^0\rightarrow SV(VS)$ and all the individual four-body decays $\bar{B}^0\rightarrow SV(VS) \rightarrow K^-π^+π^-π^+$, respectively. Our theoretical results for the two-body decays $\bar{B}^0\rightarrow \bar{K}^*(892)^0$$f_0(980)$, $\bar{B}^0\rightarrow \bar{K}^*_0(1430)^0$$ω(782)$, $\bar{B}^0\rightarrow \bar{K}^*(892)^0f_0(980)$, $\bar{B}^0\rightarrow\bar{K}^*_0(1430)^0ρ$,

hep-ph

Vector and Scalar Mesons' Mixing from QCD Sum Rules

We study $\bar qq$-hybrid mixing for the light vector mesons and $\bar qq$-glueball mixing for the light scalar mesons in Monte-Carlo based QCD Laplace sum rules. By calculating the two-point correlation function of a vector $\bar qγ_μq$ (scalar $\bar q q$) current and a hybrid (glueball) current we are able to estimate the mass and the decay constants of the corresponding mixed "physical state" that couples to both currents. Our results do not support strong quark/gluonic mixing for either the $1^{--}$ or the $0^{++}$ states.

hep-ph

Exotic tetraquark states with $J^{PC}=0^{+-}$

We use the Laplace/Borel sum rules (LSR) and the finite energy/local duality sum rules (FESR) to investigate the non-strange $ud\bar u\bar d$ and hidden-strange $us\bar u\bar s$ tetraquark states with exotic quantum numbers $J^{PC}=0^{+-}$ . We systematically construct all eight possible tetraquark currents in this channel without covariant derivative operator. Our analyses show that the $ud\bar u\bar d$ systems have good behaviour of sum rule stability and expansion series convergence in both the LSR and FESR analyses, while the LSR for the $us\bar u\bar s$ states do not associate with convergent OPE series in the stability regions and only the FESR can provide valid results. We give the mass predictions $1.43\pm0.09$ GeV and $1.54\pm0.12$ GeV for the $ud\bar u\bar d$ and $us\bar u\bar s$ tetraquark states, respectively. Our results indicate that the $0^{+-}$ isovector $us\bar u\bar s$ tetraquark may only decay via weak interaction mechanism, e.g. $X_{us\bar{u}\bar{s}}\to Kππ$, since its strong decays are forbidden by kinematics and the symmetry constraints on the exotic quantum numbers. It is predicted to be very narrow, if it does exist. The $0^{+-}$ isoscalar $us\bar u\bar s$ tetraquark is also predicted to be not very wide because its dominate decay mode $X_{us\bar{u}\bar{s}}\toϕππ$ is in $P$-wave.

hep-ph

The Mass and Decay Properties of the $1^{-+}$ Light Hybrid Meson

We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the ($1^{-+}$,$0^{++}$) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of $\langle g^3G^3\rangle$ increase the QCD sum rule mass prediction for the $1^{-+}$ light hybrid. The obtained conservative mass range 1.72--2.60 GeV does not favor the $π_1(1400)$ and the $π_1(1600)$ to be pure hybrid states and suggests the $π_1(2015)$ observed by E852 is more likely to have much of a hybrid constituent. We also study the $b_1π$ and $ρπ$ decay patterns of the $1^{-+}$ light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the $b_1π$ mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the $ρπ$ mode is small due to the absence of the leading twist contribution in the light-cone expansion of the correlation function.

hep-ph

Constraint on the light quark mass $m_q$ from QCD Sum Rules in the $I=0$ scalar channel

In this paper, we reanalyze the $I=0$ scalar channel with the improved Monte-Carlo based QCD sum rules, which combines the rigorous Hölder-inequality-determined sum rule window and a two Breit-Wigner type resonances parametrization for the phenomenological spectral density that satisfies the the low-energy theorem for the scalar form factor. Considering the uncertainties of the QCD parameters and the experimental masses and widths of the scalar resonances $σ$ and $f_0(980)$, we obtain a prediction for light quark mass $m_q(2\,\textrm{GeV})$ = $\frac{1}{2}(m_u(2\,\textrm{GeV})$ + $m_d(2\,\textrm{GeV}))$ = $4.7^{+0.8}_{-0.7}\,\textrm{MeV}$, which is consistent with the PDG (Particle Data Group) value and QCD sum rule determinations in the pseudoscalar channel. This agreement provides a consistent framework connecting QCD sum rules and low-energy hadronic physics. We also obtain the decay constants of $σ$ and $f_0(980)$ at 2 GeV, which are approximately $0.64-0.83$ GeV and $0.40-0.48$ GeV respectively.

hep-ph

A comprehensive revisit of the $ρ$ meson with improved Monte-Carlo based QCD sum rules

We improve the Monte-Carlo based QCD sum rules by introducing the rigorous Hölder-inequality-determined sum rule window and a Breit-Wigner type parametrization for the phenomenological spectral function. In this improved sum rule analysis methodology, the sum rule analysis window can be determined without any assumptions on OPE convergence or the QCD continuum.Therefore an unbiased prediction can be obtained for the phenomenological parameters (the hadronic mass and width etc.). We test the new approach in the $ρ$ meson channel with re-examination and inclusion of $α_s$ corrections to dimension-4 condensates in the OPE. We obtain results highly consistent with experimental values. We also discuss the possible extension of this method to some other channels.

hep-ph

Investigation of the light four-quark states with exotic $J^{PC}=0^{--}$

We study the exotic $J^{PC}=0^{--}$ four-quark states in Laplace sum rules (LSR) and finite energy sum rules (FESR). We use the vector tetraquark-like currents as interpolating currents in the correlator, from which the $1^{+-}$ states are also studied. In the mass extraction, we use the standard stability criterion with respect to the Borel parameters and the QCD continuum thresholds and consider the effect of the violation of factorization in estimating the high dimensional condensates as a source of uncertainties. The obtained mass prediction $1.66\pm0.14$ GeV is much lower than the previous sum rule predictions obtained using the scalar currents. Our result favours the four-quark interpretation of the possible $ρπ$ dominance in the $D^0$ decay. We also discuss the possible decay patterns of these exotic four-quark states.

hep-ph

New predictions on the mass of the $1^{-+}$ light hybrid meson from QCD sum rules

We calculate the coefficients of the dimension-8 quark and gluon condensates in the current-current correlator of $1^{-+}$ light hybrid current $g\bar{q}(x)γ_νiG_{μν}(x)q{(x)}$. With inclusion of these higher-power corrections and updating the input parameters, we re-analyze the mass of the $1^{-+}$ light hybrid meson from Monte-Carlo based QCD sum rules. Considering the possible violation of factorization of higher dimensional condensates and variation of $\langle g^3G^3\rangle$, we obtain a conservative mass range 1.72--2.60\,GeV, which favors $π_{1}(2015)$ as a better hybrid candidate compared with $π_{1}(1600)$ and $π_{1}(1400)$.

hep-ph