arXiv subjects

Xiao-Hai Liu

Publications and source records attributed to Xiao-Hai Liu.

At least 19 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.

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arXiv2026

Construction of the $a_4$ family

The COMPASS Collaboration recently reported a new broad $J^{PC}=4^{++}$ structure, denoted as $a_4(2610)$, which has sparked our interest in studying the $a_4$ family with $I^GJ^{PC}=1^{-}4^{++}$. In this work, we investigate the mass spectra and Okubo-Zweig-Iizuka-allowed two-body strong decays of the $a_4$ family using the modified Godfrey-Isgur quark model and the quark-pair creation model. We also explore the possibility of identifying $a_4(2610)$ as a $4F$ or $2H$ state, and our numerical results suggest that it could be a promising candidate for the $a_4(2H)$ state. In addition, we predict the masses and the widths of the $a_4(1H)$ and $a_4(3F)$ states.

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arXiv2026

Production of hidden-charm molecular candidates in $ψ(4660)$ decays

We investigate the production of several hidden-charm exotic candidates, including $Z_c(3900)$, $Z_c(4020)$, $Z_{cs}(3985)$, and $Z_2(4250)$, in $ψ(4660)$ decays under the assumption that these states are predominantly hadronic molecules. Treating $ψ(4660)$ as a conventional $ψ(5S)$ charmonium state, the production mechanisms are described through intermediate charmed-meson triangle loops, with its couplings to charmed-meson pairs estimated within the quark model. A systematic analysis of the processes $ψ(4660)\to Z_c(3900)π$, $ψ(4660)\to Z_c(4020)π$, $ψ(4660)\to Z_{cs}(3985)K$, and $ψ(4660)\to Z_2(4250)π$ is performed within a unified framework. The predicted branching fractions are found to be of the order of $10^{-2}$, $10^{-4}$, $10^{-3}$, and $10^{-6}$, respectively, exhibiting only a mild dependence on the cutoff parameter. We further find that the contributions from the $SHH$ intermediate loops dominate over those from the $THH$ and $HHH$ loops in most channels. The sizable production rates obtained in this work indicate that $ψ(4660)$ decays provide a promising platform for probing the molecular nature of charged hidden-charm exotic states and testing their underlying production mechanisms.

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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.

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arXiv2026

Probing the nature of $D_1 K$ and $D_2 K$ molecules through $D_s^{(*)}ππ$ and $D_{s0(s1)}π$ decays

We study the two- and three-body decays of the $I=0$ $D_1K$ and $D_2K$ molecular states $T_{c\bar{s}1}^*$ and $T_{c\bar{s}2}^*$ into $D_s^{(*)}$ mesons and pions. Triangle singularities produce narrow peaks in the $D_s^*π$ and $D_sπ$ invariant mass spectra near the $D^*K$ and $DK$ thresholds. The isospin-violating two-body decays $T_{c\bar{s}1}^*\to D_{s1}(2460)π^0$, $T_{c\bar{s}2}^*\to D_{s1}(2460)π^0$, and $T_{c\bar{s}2}^*\to D_{s0}^*(2317)π^0$ exhibit large partial widths, reflecting the strong couplings inherent to molecular states. These predictions, obtained within heavy hadron chiral perturbation theory and the chiral unitary approach, provide complementary signatures for identifying $D_1K$ and $D_2K$ molecules at experiments.

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arXiv2025

New spectrum of charm-strange meson with constituent quark model $c\bar{s}$ contributions

We systematically investigate the $S$-wave interactions between Nambu-Goldstone bosons (NGBs) and charmed mesons in the $(S,I)=(1,0)$ sector using the chiral unitary approach. The scattering amplitudes incorporate both the Weinberg-Tomozawa term and additional contributions from $s$- and $u$-channel exchanges of $c\bar{s}$ states predicted by the constituent quark model (CQM). Through analytic continuation of the unitarized amplitudes to the complex energy plane, we identify multiple poles corresponding to bound states and resonances. Our analysis reveals a rich spectrum of $D_{sJ}$ states across $J^P = 0^+, 1^+, 1^-$, and $2^-$ sectors, providing new insights into the nature of established resonances like $D_{s0}^*(2317)$ and $D_{s1}(2460)$, while predicting several new states that could be observed in future experiments.

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arXiv2025

High spin kaons

The COMPASS Collaboration recently reported the observation of strange-meson spectra in the reaction $K^- + p \to K^- π^- π^+ + p$ and found $K_3$ and $K_4$ states, with masses of $2119 \pm 13 ^{+45}_{-12}$ MeV and $2210 \pm 40 ^{+80}_{-30}$ MeV, respectively. This discovery has significantly renewed interest, prompting a detailed and systematic study of high-spin kaons. In this work, we analyze the mass spectrum and the Okubo-Zweig-Iizuka-allowed two-body strong decay properties of high-spin kaons having $J^P=3^{\pm}, 4^{\pm}$, and $5^{\pm}$ within the framework of the modified Godfrey-Isgur model and the $^3P_0$ model. Moreover, we identify critical decay channels, which may serve as useful guidance for future experimental studies.

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arXiv2025

Threshold effects as the origin of $Y(4500)$ observed in $e^+e^-\to J/ψK^+K^-$

The BESIII collaboration has recently observed a resonant structure $Y(4500)$ in $e^{+}e^{-}\to J/ψK^{+}K^{-}$, whose origin remains unresolved. In this study, we analyze the cross section line shape of $e^{+}e^{-}\to J/ψK^{+}K^{-}$ by taking into account the $ψ(4415)$ state and intermediate charmed meson loops. By treating $ψ(4415)$ as both a pure $S$-wave state and $S$-$D$ mixed states, and introducing the $Z_{cs}^{(\prime)}$ resonance, we find that the $Y(4500)$ peak at $\sqrt{s}=4.5~\text{GeV}$ arises from the triangle singularity mechanism in the $Z_{cs}^{(\prime)}$-mediated rescattering processes, supporting its interpretation as a threshold effect rather than a conventional resonance.

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arXiv2025

Shedding light on the nature of $ϕ(2170)$ state in the $e^+e^- \to ϕπ^+π^-$ reaction

We investigate the production of $ϕ(2170)$ state in the $e^+e^- \to ϕπ^+π^-$ reaction with the effective Lagrangian approach. In addition to the tree level contributions from the $ϕ(1680)$ meson and a possible X(1750) state, we consider also the $K_1$-$K$-$\bar{K}$ intermediate state process from the perspective of triangular singularity. Based on the one-photon exchange approximation, a pair of $K_1 \bar{K}$ mesons was firstly produced, and then the $K_1$ meson subsequently decays into $ϕ$ and $K$, and the $K\bar{K}$ pair produce the $π^+ π^-$ through the final state interactions, in which the scalar meson $f_0(980)$ is dynamically generated. We show that the inclusion of the triangle loop diagrams leads to a good description of the new BESIII measurements, especially for the structure of $ϕ(2170)$. This provides a novel interpretation of the $ϕ(2170)$ state, offering new insights into its fundamental nature which is still unclear. Furthermore, it is found that these measurements on the $e^+e^- \to ϕπ^+π^-$ reaction can be used to determine some of the properties of two $K_1$ mesons with masses around 1610 MeV and 1895 MeV, which are crucial to reproduce the experimental data.

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arXiv2025

The new states $X(1910)$ and $X(2300)$ and higher light excited $J^{PC}=1^{+-}$ mesons

The BESIII Collaboration recently reported the observation of two new resonances, $X(1910)$ and $X(2300)$, which have sparked our interest in studying the light hadron family with $J^{PC}=1^{+-}$ . In this work, we investigate the mass spectra and OZI-allowed two-body strong decays of $b_1$, $h_1$, and $h_1^\prime$ using the MGI model and QPC model with newly fitted parameters. We also explore the possibility of identifying $X(1910)$ and $X(2300)$ as $h_1$ or $h_1^\prime$ states. Our numerical results suggest that $X(1910)$ could be a promising candidate for the $h_1^\prime(2^1P_1)$ state with quark content $s\bar{s}$, while the structure of $X(2300)$ remains uncertain.

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arXiv2025

Production and decay of anticharmed pentaquark state with quark content $\bar{c}sudd$

We used an effective Lagrangian approach to investigate the production of the anticharmed pentaquark state $P_{\bar{c}s}^{(*)-}$ with the minimal quark content $\bar{c}sudd$ in the $Λ_b^0$ decay and its decay into the $ΛD^{(\ast)-}$ and $ΣD^{(\ast)-}$. In our calculation, the $P_{\bar{c}s}^{(*)-}$ is considered as the molecule state of the $nD_{s0(s1)}^{-}$ in an $S$ wave, and its production and decay occur via triangle loops at the hadron level. The predicted branching fractions for the processes $Λ_b^0\to P_{\bar{c}s}^{(*)-} D^+ $ are around $10^{-4}\sim 10^{-3}$. The partial decay widths of the $ P_{\bar{c}s}^{(*)-} \to ΛD^{(\ast)-}$ are between $0.1$ and $\sim 10~\mathrm{MeV}$, whereas the decay widths of the $ P_{\bar{c}s}^{(*)-} \to ΣD^{(\ast)-}$ are about one order of magnitude smaller. It is found that the width ratios for the $P_{\bar{c}s}^{(*)-}$ decays are nearly independent of the model parameter $α$. It is hoped that these predictions could be helpful in searching for the anticharmed-strange pentaquark candidates in future LHCb experiments.

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arXiv2024

Pionic transitions of the spin-2 partner of $X(3872)$ to $χ_{cJ}$

We investigated the pionic transitions between the $X_2$ [spin-2 partner of the $X(3872)$] and $χ_{c1,2}$ using a nonrelativistic effective field theory. The $X_2$ is assumed to be a bound state of the $D^{*}$ and $\bar{D}^*$ mesons and to decay through several kinds of loops, including the bubble, triangle and box loops. Within the present model, the widths for the single-pion decays $X_2\toπ^0χ_{cJ}$ are predicted to be about $3$--$30$ keV. For the dipion decays, the widths are a few keVs. These widths yield a branching fraction of $10^{-3}$--$10^{-2}$. The ratio $R_{\mathrm{c}0}=Γ(X_2\toπ^+π^-χ_{cJ})/Γ(X_2\toπ^0π^0χ_{cJ}) \simeq 1.6$, which is a bit smaller than the expected value of $2$, and $R_{21}=Γ(X_2\toππχ_{c2})/Γ(X_2\toππχ_{c1}) \simeq 0.85$. These ratios are nearly independent of the $X_2$ mass and the coupling constants, which might be a good quantity for the experiments. Moreover, the invariant mass spectra of the $π^0χ_{cJ}$ final state for the dipion processes are presented, showing a cusp structure at the $D {\bar D}^*$ threshold enhanced and narrowed by the nearby triangle singularity.

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arXiv2024

Identifying the two-pole structure of the $Λ(1405)$ using an SU(3) flavor filter

We propose a novel method to identify the two-pole structure of the $Λ(1405)$. The two poles owe their origin to different quark flavor irreducible representations in the meson-baryon coupled-channel interactions, thus they should be individually manifested in reactions that provide good flavor eigenstate sources. Hadronic decays of charmonia into $\barΛΣπ$ and $\barΛ(1520)Σπ$ are such reactions, and the flavor octet and singlet poles can be approximately singled out in these two decay modes. This SU(3) flavor filter works even considering the flavor symmetry breaking. With the huge charmonium data sets collected, it is therefore promising to solve the long-standing $Λ(1405)$ puzzle employing the proposed flavor filter.

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arXiv2024

Weak decays of the triply heavy baryons in the three-quark picture with the light-front quark model

We investigate the weak decays of the triply heavy baryon $Ω_{QQQ}$ in the light-front quark model. Since $Ω_{QQQ}$ consists of three indistinguishable identical heavy quarks, the commonly adopted quark-diquark picture does not seem to be valid anymore. Instead, we employ the three-quark picture for baryons where the three quarks are regarded as individual quarks. We calculate the hadronic form factors for the transitions and give predictions for the decay widths of the semi-leptonic decay modes $Ω_{ccc}\to Ξ_{cc}/ Ω_{cc}+ l\barν_l$, $Ω_{bbb}\to Ξ_{bb}+ l \barν_l$ and the non-leptonic decay modes $Ω_{ccc}\to Ξ_{cc}/Ω_{cc}+ M$, $Ω_{bbb}\to Ξ_{bb}+ M$. Our study can be a guide for future experiments to discover the triply heavy baryons.

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arXiv2023

Study on the possible molecular states composed of $Λ_c\bar D^$, $Σ_c\bar D^$, $Ξ_c\bar D^$ and $Ξ_c'\bar D^$ in the Bethe-Salpeter frame based on the pentaquark states $P_c(4440)$, $P_c(4457)$ and $P_{cs}(4459)$

The measurements on a few pentaquarks states $P_c(4440)$, $P_c(4457)$ and $P_{cs}(4459)$ excite our new interests about their structures. Since the masses of $P_c(4440)$ and $P_c(4457)$ are close to the threshold of $Σ_c\bar D^*$, in the earlier works, they were regarded as molecular states of $Σ_c\bar D^*$ with quantum numbers $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$ and $\frac{1}{2}(\frac{3}{2}^-)$, respectively. In a similar way $P_{cs}(4459)$ is naturally considered as a $Ξ_c\bar D^*$ bound state with $I=0$. Within the Bethe-Salpeter (B-S) framework we systematically study the possible bound states of $Λ_c\bar D^*$, $Σ_c\bar D^*$, $Ξ_c\bar D^*$ and $Ξ_c'\bar D^*$. Our results indicate that $Σ_c\bar D^*$ can form a bound state with $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$, which corresponds to $P_c(4440)$. However for the $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$ system the attraction between $Σ_c$ and $\bar D^*$ is too weak to constitute a molecule, so $P_{c}(4457)$ may not be a bound state of $Σ_c\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$. As $Ξ_c\bar D^*$ and $Ξ_c'\bar D^*$ systems we take into account of the mixing between $Ξ_c$ and $Ξ'_c$ and the eigenstets should include two normal bound states $Ξ_c\bar D^*$ and $Ξ_c'\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$ and a loosely bound state $Ξ_c\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$. The conclusion that two $Ξ_c\bar D^*$ bound states exist, supports the suggestion that the observed peak of $P_{cs}(4459)$ may hide two states $P_{cs}(4455)$ and $P_{cs}(4468)$. Based on the computations we predict a bound state $Ξ_c'\bar D^*$ with $I(J^P)=\frac{1}{2}(\frac{1}{2}^-)$ but not that with $I(J^P)=\frac{1}{2}(\frac{3}{2}^-)$. Further more accurate experiments will test our approach and results.

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arXiv2023

Study on the weak decay between two heavy baryons $ \mathcal{B}_i(\frac{1}{2}^+)\to \mathcal{B}_f(\frac{3}{2}^+)$ in the light-front quark model

In this work, we study the weak decay between two heavy baryons $ \mathcal{B}_i(\frac{1}{2}^+)\to \mathcal{B}_f(\frac{3}{2}^+)$ in the light-front quark model where three-quark picture is employed for baryon. We derive general form of transition amplitude of $ \mathcal{B}_i(\frac{1}{2}^+)\to \mathcal{B}_f(\frac{3}{2}^+)$, and analyze two specific cases of transitions: the weak decays of single heavy baryon $Σ_{b} \to Σ_{c}^*$ and the decays of double-charmed baryon $Ξ_{cc}\to Σ_{c}^*(Ξ_{c}^*)$. We compute the hadronic form factors for the transitions and apply them to study the decay widths of the semi-leptonic $\mathcal B_i(\frac{1}{2}^+)\to\mathcal B_f(\frac{3}{2}^+) l\barν_l$ and non-leptonic $\mathcal B_i(\frac{1}{2}^+)\to\mathcal B_f(\frac{3}{2}^+)M$. Previously we studied the transition $Σ_{b} \to Σ_{c}^*$ with the quark-diquark picture of baryon in the light-front quark model. Here we revisit this transition with three-quark picture of baryon. At the quark level, the transition $Σ_{b} \to Σ_{c}^*$ is induced by the $b\rightarrow c$ transition.The subsystem of the two unchanged light quarks which possesses definite and same spin in initial and final state can be viewed as a spectator, so the spectator approximation can be applied directly. For the weak decay of doubly charmed baryon $Ξ_{cc}$, a $c$ quark decays to a light quark $q_1$, so both the initial state $cc$ and final state $q_1q_2$ ($q_1$ and the original $q_2$ in initial state may be the same flavor quarks) which possess definite spin are no longer spectators. A rearrangement of quarks for initial and final states is adopted to isolate the unchanged subsystem $cq_2$ which can be viewed as the spectator approximately. Future measurements on these channels will constrain the nonperturbative parameter in the wavefunctions and test the model predictions.

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arXiv2023

Searching for doubly charmed tetraquark candidates $T_{cc}$ and $T_{cc\bar{s}}$ in $B_c$ decays

In this work, we propose to search for the exotic doubly charmed meson $T_{cc}^+$ and its analog $T_{cc\bar{s}}^+$ in $B_c^+$ decays, which provide a good environment for the formation of the exotic state containing double charm quarks. Within the molecular scheme, the production of $T_{cc}^+$ and $T_{cc\bar{s}}^+$ through various rescattering processes with different intermediate states are investigated. For the moderate values of model parameters, the branching ratios of $B_c^+$ decaying into $T_{cc}^+ \bar{D}^{0}$, $T_{cc}^+ \bar{D}^{*0}$, $T_{cc\bar{s}}^+ \bar{D}^{0}$ and $T_{cc\bar{s}}^+ \bar{D}^{*0}$ are estimated to be of the order of $10^{-7}$, $10^{-5}$, $10^{-6}$ and $10^{-4}$, respectively, which may be tested by future experiments.

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arXiv2022

Possible molecular states of $\bar D^{}K^{}$ ($ D^{}K^{}$) and the new exotic states $X_0(2900)$ and $X_1(2900)$ ($T^a_{cs0}(2900)^0$ and $T^a_{cs0}(2900)^{++}$)

Two iso-singlet hadron states $X_0(2900)$ and $X_1(2900)$ with $J=0$ and 1 respectively, discovered by the LHCb collaboration in 2020, were identified as molecular bound states of $\bar D^*K^*$. Recently two structures $T^a_{cs0}(2900)^0$ and $T^a_{cs0}(2900)^{++}$ have been observed at the hadron spectra, one would suspect if they also are molecular states of $D^*$ and $K^*$. As long as they were of the molecular structures of $D^*K^*$, the hadron states must be in an iso-vector, namely $T^a_{cs0}(2900)^0$ and $T^a_{cs0}(2900)^{++}$ were $I_3=-1, 1$ components of the iso-vector. If it is the case, the corresponding $T^a_{cs0}(2900)^+$ of ($I=1,I_3=0$) and $T^{'a}_{cs0}(2900)^{+}$ of $I=0,I_3=0$ so far evade experimental observation, but should be found by the future experiments. To testify this ansatz, in this paper we study the possible molecular structures of $\bar D^{*}K^{*}$ and $D^{*}K^{*}$ within the Bethe-Salpeter (B-S) framework. With reasonable input parameters it is found that $\bar D^{*}K^{*}$ iso-scalar systems with $J^P=0^+$ and $1^+$ are solutions. The result supports the ansatz of $X_0(2900)$ ($X_1(2900)$) being molecular states of $\bar D^*K^{*}$. Whereas for the system of $ D^{*}K^{*}$ with $I=1$ the corresponding B-S equation has no solution. Thus we can draw a clear conclusion that $T^a_{cs0}(2900)^0$ and $T^a_{cs0}(2900)^{++}$ should not be bound states of $ D^{*}$ and $K^{*}$. The two structures observed by the LHCb collaboration may be caused by dynamics, such as the well-recognized triangle anomalies or other mechanisms.

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