arXiv subjects

Zu-Xin Cai

Publications and source records attributed to Zu-Xin Cai.

6 recordsLinked to original sources

arXiv2026

Study of the $e^+e^- \to ϕK^+K^-$ reaction within triangle dynamics and its implications for the $ϕ(2170)$

We revisit the $e^+e^- \to ϕπ^+π^-$ reaction within the $K_1$-$\bar{K}$-$K$ triangle dynamics framework, in which the $e^+e^-$ pair annihilates through one-photon exchange approximation to produce a $K_1\bar{K}$ pair, followed by the $K_1 \toϕK$ decay and the final-state $K\bar{K} \to π^+π^-$ rescattering. With the same theoretical formalism and model parameters, the $e^+e^- \to ϕK^+K^-$ reaction is investigated, and it is found that the predicted total cross sections for the $e^+ e^- \to ϕK^+ K^-$ reaction are in good agreement with the existing BESIII measurements. Our study shows that the triangle singularity in the $ϕK^+K^-$ channel is strongly suppressed, because the higher $K^+K^-$ mass threshold shifts the kinematics away from the triangle singularity condition and the phase space near the $K_1\bar{K}$ threshold is very limited. Moreover, the interference between the tree-level and loop amplitudes eliminates the remaining signal. These combined effects naturally explain the absence of a distinct $ϕ(2170)$ signal in the $e^+ e^- \to ϕK^+ K^-$ reaction, provide a strong test of the model, and reinforce the picture that both reactions are governed by the same underlying mechanism, in which the $ϕ(2170)$ state is produced in the $e^+ e^-$ annihilation from the $K_1$-$\bar{K}$-$K$ triangle loop.

hep-ph↗

arXiv2026

Final-state rescattering mechanism of the $Δ(1232)^{++}$ production in $Λ^+_c \to K^- π^+ p$ decay

We investigate the production of the $Δ(1232)^{++}$ resonance in the charmed baryon weak decay $Λ^+_c \to K^- π^+ p$, focusing on the $π^+ p$ final-state rescattering mechanism. The direct $W^+$ exchange diagram is expected to be suppressed, hence we adopt the $W^+$ internal emission process $Λ^+_c \to p \bar K^{*0}(892)$ followed by the subsequent decay $\bar{K}^{*0} \to K^- π^+$ as the dominant source of the final state particles. The $Δ(1232)^{++}$ resonance is then generated via $π^+ p$ rescattering within a triangle loop mechanism. Our calculations incorporate both the tree-level $\bar K^{*0}(892)$ and the dynamically generated $\bar{K}^*_0(700)$ state arising from the $S$-wave $K π$ final state interaction. We find that our theoretical results can reproduce the bump and peak structures in the $K^- π^+$ invariant mass distributions for the $\bar{K}^*_0(700)$ and $\bar{K}^{*0}(892)$, respectively. Meanwhile, the peak for the $Δ(1232)^{++}$ in the $π^+ p$ invariant mass distributions is also well described. The $Δ(1232)^{++}$ signal naturally emerges from rescattering effects, and adopting the pole parameters of $Δ(1232)$ resonance yields an improved description of the experimental data. In addition, we obtain a branching fraction ratio $\mathcal{B}[Λ_c^+ \to Δ(1232)^{++} K^-] / \mathcal{B}[Λ_c^+ \to p \bar{K}^{*0}(892)] \approx 0.5$, which is lower than the experimentally measured value. This discrepancy suggests that interference effects are likely significant in this decay process. Future high-precision measurements will further verify the proposed rescattering mechanism.

hep-ph↗

arXiv2025

Light hadronic decays of spin-0 partner of $X(3872)$

The $X(3872)$ is theoretically predicted to have a spin-0 partner state denoted as $X_0$. Assuming the $X_0$ as a $D\bar{D}$ molecular bound state, we calculate the decay widths of $X_0\to VV$ and $X_0 \to PP$ ($V$ and $P$ stand for light vector and pseudoscalar mesons, respectively) via intermediate charmed meson loops. Three different configurations of the $X_0$, i.e., pure neutral components ($θ= 0$), isospin singlet ($θ= π/4$) and pure charged components ($θ= π/2$), are investigated. Within a commonly accepted range of the model parameter $α$, the predicted decay widths of $X_0 \to VV$ are on the order of a few hundred $\mathrm{keV}$, while the decay widths of $X_0 \to PP$ can reach several $\mathrm{MeV}$. The $X_0 \to ρρ$ and $ππ$ have larger decay rates. The relative width ratios between the channels are nearly model-independent. Moreover, among those channels only with isovector or isoscalar mesons, the relevant ratios are also independent of the phase angle. The predicted ratios are helpful for searching the $X_0$ in the future experiments at BESIII and Belle II.

hep-ph↗

arXiv2024

Charmless decays of the spin-2 partner of $X(3872)$

The Belle collaboration recently reported a promising candidate for the spin-2 $D^*\bar{D}^*$ partner of the $X(3872)$, called the $X_2$ for short, having a mass of $(4014.3 \pm 4.0 \pm 1.5)~\mathrm{MeV}$ and a width of $(4 \pm 11 \pm 6)~\mathrm{MeV} $. In present work, we assume the $X_2$ as a pure molecule of the $D^*\bar{D}^*$ under three cases, i.e., pure neutral components ($θ= 0$), isospin singlet ($θ= π/4$) and neutral components dominant ($θ= π/6$), where $θ$ is a phase angle describing the proportion of neutral and charged constituents. Using an effective Lagrangian approach, we calculated the partial widths of $X_2\to VV$ and $X_2 \to PP$ ($V$ and $P$ stand for light vector and pseudoscalar mesons, respectively). The predicted decay widths of $X_2 \to VV$ can reach a few hundreds of $\mathrm{keV}$, while the decay widths of $X_2 \to PP$ are about several tens of $\mathrm{keV}$. In addition, the effects from the proportion of neutral and charged constituent on the decay widths of $X_2\to VV$ and $PP$ are also investigated. We hope that the present calculations will be checked experimentally in the future.

hep-ph↗

arXiv2024

Production of $X_b$ via radiative transition of $Υ(10753)$

We studied the radiative transitions between the $Υ(10753)$, the $S$-$D$ mixed state of the $Υ(4S)$ and $Υ_1(3\,{}^3D_1)$, and the $X_b$, the heavy quark flavor symmetry counterpart of the $X(3782)$ in the bottomonium sector. The radiative transition was assumed to occur through the intermediate bottom mesons, including $P$-wave $B_1^{(\prime)}$ mesons as well as the $S$-wave $B^{(*)}$ ones. The consideration of the $B_1^{(\prime)}$ mesons leads to the couplings to be in $S$-wave, and hence enhances the contributions of the intermediate meson loops. The radiative decay width for the $Υ(10753)\toγX_b$ is predicted to be order of $10~\mathrm{keV}$, corresponding to a branching fraction of $10^{-4}$. Based on the theoretical results, we strongly suggest to search for the $X_b$ in the $e^+e^-\toγX_b$ with $X_b\toππχ_{b1}$ near $\sqrt{s}=10.754~\mathrm{GeV}$, and it is hoped that the calculations here could be tested by the future Belle II experiments.

hep-ph↗

arXiv2023

Production of $X_b$ via $Υ(5S, 6S)$ radiative decays

We investigate the production of $X_b$ in the process $Υ(5S,6S)\to γX_b$, where $X_b$ is assumed to be a $B {\bar B}^*$ molecular state. Two kinds of meson loops of $B^{(*)}{\bar B}^{(*)}$ and $B_1^{\prime}{\bar B}^{(*)}$ were considered. To explore the rescattering mechanism, we calculated the relevant branching ratios using the effective Lagrangian based on the heavy quark symmetry. The branching ratios for the $Υ(5S\,,6S) \to γX_b$ were found to be at the orders of $10^{-7} \sim 10^{-6}$. Such sizeable branching ratios might be accessible at BelleII, which would provide important clues to the inner structures of the exotic state $X_b$.

hep-ph↗