arXiv subjects

Wei-Hong Liang

Publications and source records attributed to Wei-Hong Liang.

At least 55 records · Page 3Linked to original sources

arXiv2021

Analysis of the $ \boldsymbol{γγ\to D\bar D}$ reaction and the $D\bar{D}$ bound state

In this work, we investigate the reaction of $γγ\to D\bar{D}$, taking into account the s-wave $D\bar{D}$ final state interaction. By fitting to the $D\bar{D}$ invariant mass distributions measured by the Belle and BaBar Collaborations, we obtain a good reproduction of the data by means of a $D\bar{D}$ amplitude that produces a bound $D\bar{D}$ state with $I=0$ close to threshold. The error bands of the fits indicate, however, that more precise data on this reaction are needed to be more assertive about the position and width of such state.

hep-ph↗

arXiv2021

Analysis of the $ \boldsymbol{e^+ e^- \to J/ψD\bar D}$ reaction close to the threshold concerning claims of a $χ_{c0}(2P)$ state

We analyze the $D\bar{D}$ mass distribution from a recent Belle experiment on the $e^+e^- \to J/ψD\bar{D}$ reaction, and show that the mass distribution divided by phase space does not have a clear peak above the $D\bar{D}$ threshold that justifies the experimental claim of a $χ_{c0}(2P)$ state from those data. Then we use a unitary formalism with coupled channels $D^+D^-$, $D^0\bar{D}^0$, $D_s\bar{D}_s$, and $ηη$, with some of the interactions taken from a theoretical model, and use the data to fix other parameters. We then show that, given the poor quality of the data, we can get different fits leading to very different $D\bar{D}$ amplitudes, some of them supporting a $D\bar{D}$ bound state and others not. The main conclusion is that the claim for the $χ_{c0}(2P)$ state, already included in the PDG, is premature, but refined data can provide very valuable information on the $D\bar{D}$ scattering amplitude. As side effects, we warn about the use of a Breit-Wigner amplitude parameterization close to threshold, and show that the $D_s\bar{D}_s$ channel plays an important role in this reaction.

hep-ph↗

arXiv2020

$Ξ_{bb}$ and $Ω_{bbb}$ molecular states

Using the vector-exchange interaction in the local hidden gauge approach, which in the light quark sector generates the chiral Lagrangian, and has produced realistic results for $Ω_c, Ξ_c, Ξ_b$ and the hidden charm pentaquark states, we study the meson-baryon interactions in the coupled channels that lead to the $Ξ_{bb}$ and $Ω_{bbb}$ excited states of the molecular type. We obtain seven states of the $Ξ_{bb}$ type with energies between $10408$ and $10869$ MeV and one $Ω_{bbb}$ state at $15212$ MeV.

hep-ph↗

arXiv2020

Observed $Ω_b$ spectrum and meson-baryon molecular states

We observe that four peaks seen in the high energy part of the $Ω_b$ spectrum of the recent LHCb experiment are in remarkable agreement with predictions made for molecular $Ω_b$ states stemming from the meson-baryon interaction, with an approach that applied to the $Ω_c$ states gave rise to three states in good agreement with experiment in masses and widths. While the statistical significance of the peaks prevents us from claims of states at the present time, the agreement found should be an incentive to look at this experiment with increased statistics to give an answer to this suggestive idea.

hep-ph↗

arXiv2020

$Υ(nl)$ decay into $ B^{()} \bar B^{()}$

We have evaluated the decay modes of the $Υ(4s), Υ(3d), Υ(5s), Υ(6s)$ states into $B\bar B, B\bar B^*+c.c., B^* \bar B^*, B_s \bar B_s, B_s \bar B^*_s +c.c., B^*_s \bar B_s^* $ using the $^3P_0$ model to hadronize the $b\bar b$ vector seed, fitting some parameters to the data. We observe that the $Υ(4s)$ state has an abnormally large amount of meson-meson components in the wave function, while the other states are largely $b\bar b$. We predict branching ratios for the different decay channels which can be contrasted with experiment for the case of the $Υ(5s)$ state. While globally the agreement is fair, we call the attention to some disagreement that could be a warning for the existence of more elaborate components in the state.

hep-ph↗

arXiv2020

Signatures of the two $K_1(1270)$ poles in $D^+\to νe^+ V P$ decay

We analyze theoretically the $D^+\to νe^+ ρ\bar K$ and $D^+\to νe^+ \bar K^* π$ decays to see the feasibility to check the double pole nature of the axial-vector resonance $K_1(1270)$ predicted by the unitary extensions of chiral perturbation theory (UChPT). Indeed, within UChPT the $K_1(1270)$ is dynamically generated from the interaction of a vector and a pseudoscalar meson, and two poles are obtained for the quantum numbers of this resonance. The lower mass pole couples dominantly to $K^*π$ and the higher mass pole to $ρK$, therefore we can expect that different reactions weighing differently these channels in the production mechanisms enhance one or the other pole. We show that the different final $VP$ channels in $D^+\to νe^+ V P$ weigh differently both poles, and this is reflected in the shape of the final vector-pseudoscalar invariant mass distributions. Therefore, we conclude that these decays are suitable to distinguish experimentally the predicted double pole of the $K_1(1270)$ resonance.

hep-ph↗

arXiv2020

Theoretical interpretation of the $D^+_s \to π^+ π^0 η$ decay and the nature of $a_0(980)$

In a recent paper \cite{Ablikim:2019pit}, the BESIII collaboration reported the so-called first observation of pure $W$-annihilation decays $D^+_s \to a^+_0(980) π^0$ and $D_s^+ \to a^0_0(980)π^+$. The measured absolute branching fractions are, however, puzzlingly larger than those of other measured pure $W$-annihilation decays by at least one order of magnitude. In addition, the relative phase between the two decay modes is found to be about 180 degrees. In this letter, we show that all these can be easily understood if the $a_0(980)$ is a dynamically generated state from $\bar{K} K$ and $πη$ interactions in coupled channels. In such a scenario, the $D^+_s$ decay proceeds via internal $W$ emission instead of $W$-annihilation, which has a larger decay rate than $W$-annihilation. The proposed decay mechanism and the molecular nature of the $a_0(980)$ also provide a natural explanation to the measured negative interference between the two decay modes.

hep-ph↗

arXiv2020

$J/ψ\to γππ$, $γπ^0η$ reactions and the $f_0(980)$ and $a_0(980)$ resonances

We study the $J/ψ\to γπ^+ π^-$, $γπ^0 η$ reactions from the perspective that they come from the $J/ψ\to ϕ(ω) π^+ π^-, ρ^0π^0 η$ reactions, where the $ρ^0$, $ω$, and $ϕ$ get converted into a photon via vector meson dominance. Using models successfully used previously to study the $J/ψ\to ω(ϕ) ππ$ reactions, we make determinations of the invariant mass distributions for $π^+ π^-$ in the regions of the $f_0(500)$, $f_0(980)$, and for $π^0 η$ in the region of the $a_0(980)$. The integrated differential widths lead to branching ratios below present upper bounds, but they are sufficiently large for future check in updated facilities.

hep-ph↗

arXiv2020

Testing the origin of the "$f_1(1420)$" with the $\bar K p \to Λ(Σ) K\bar K π$ reaction

We study the $\bar K p \to Y K\bar K π$ reactions with $\bar K = \bar K^0, K^-$ and $Y=Σ^0, Σ^+, Λ$, in the region of $K\bar K π$ invariant masses of $1200-1550$ MeV. The strong coupling of the $f_1(1285)$ resonance to $K^* \bar K$ makes the mechanism based on $K^*$ exchange very efficient to produce this resonance observed in the $K\bar K π$ invariant mass distribution. In addition, in all the reactions one observes an associated peak at $1420$ MeV which comes from the $K^* \bar K$ decay mode of the $f_1(1285)$ when the $K^*$ is placed off shell at higher invariant masses. We claim this to be the reason for the peak of the $K^* \bar K$ distribution seen in the experiments which has been associated to the "$f_1(1420)$" resonance.

hep-ph↗

arXiv2019

Molecular $Ξ_{bc}$ states from meson-baryon interaction

We have studied the meson-baryon interaction in coupled channels with the same quantum numbers of $Ξ_{bc}$. The interaction is attractive in some channels and of sufficient intensity to lead to bound states or resonances. We use a model describing the meson-baryon interaction based on an extrapolation of the local hidden gauge approach to the heavy sector, which has been successfully used in predicting $Ω_c$ and hidden charm states. We obtain many states, some of them narrow or with zero width, as a consequence of the interaction, which qualify as molecular states in those channels. The success in related sectors of the picture used should encourage the experimental search for such states.

hep-ph↗

arXiv2019

$χ_{c1}$ decays into a pseudoscalar meson and a vector-vector molecule

We evaluate ratios of the $χ_{c1}$ decay rates to $η$ ($η', K^-$) and one of the $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f_2'(1525)$, $K^{*}_2(1430)$ resonances, which in the local hidden gauge approach are dynamically generated from the vector-vector interaction. With the simple assumption that the $χ_{c1}$ is a singlet of SU(3), and the input from the study of these resonances as vector-vector molecular states, we describe the experimental ratio $\mathcal{B}(χ_{c1} \rightarrow ηf_2(1270))/ \mathcal{B}(χ_{c1} \rightarrow η' f_2'(1525))$ and make predictions for six more ratios that can be tested in future experiments.

hep-ph↗

arXiv2019

The $χ_{cJ}$ decay to $ϕK^* \bar K, ϕh_1(1380)$ testing the nature of axial vector meson resonances

We perform a theoretical study of the $χ_{cJ} \to ϕK^* \bar K \to ϕKπ\bar K$ reaction taking into account the $K^* \bar K$ final state interaction, which in the chiral unitary approach is responsible, together with its coupled channels, for the formation of the low lying axial vector mesons, in this case the $h_1(1380)$ given the selection of quantum numbers. Based on this picture we can easily explain why in the $χ_{c0}$ decay the $h_1(1380)$ resonance is not produced, and, in the case of $χ_{c1}$ and $χ_{c2}$ decay, why a dip in the $K^+ π^0 K^-$ mass distribution appears in the 1550-1600 MeV region, that in our picture comes from a destructive interference between the tree level mechanism and the rescattering that generates the $h_1(1380)$ state. Such a dip is not reproduced in pictures where the nominal $h_1(1380)$ signal is added incoherently to a background, which provides support to the picture where the resonance appears from rescattering of vector-pseudoscalar components.

hep-ph↗

arXiv2019

Triangle singularity in the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ decays

We study the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ reaction and find that the mechanism to produce this decay develops a triangle singularity around $M_{\rm inv}(K^- f_0/K^- a_0) \approx 1515$~MeV. The differential width $dΓ/ dM_{\rm inv}(K^- f_0/K^- a_0)$ shows a rapid growth around the invariant mass being 1515~MeV as a consequence of the triangle singularity of this mechanism, which is directly tied to the nature of the $f_0(980)$ and $a_0(980)$ as dynamically generated resonances from the interaction of pseudoscalar mesons. The branching ratios obtained for the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ decays are of the order of $10^{-5}$, accessible in present facilities, and we argue that their observation should provide relevant information concerning the nature of the low-lying scalar mesons.

hep-ph↗

arXiv2019

Theoretical description of the $\boldsymbol{J/ψ\to η(η') h_1(1380)}$, $\boldsymbol{J/ψ\to η(η') h_1(1170)}$ and $\boldsymbol{J/ψ\to π^0 b_1(1235)^0}$ reactions

We have made a study of the $J/ψ\to η' h_1, ηh_1$ (with $h_1$ being $h_1(1170)$ and $h_1(1380)$) and $J/ψ\to π^0 b_1(1235)^0$ assuming the axial vector mesons to be dynamically generated from the pseudoscalar-vector meson interaction. We have taken the needed input from previous studies of the $J/ψ\to ϕππ, ωππ$ reactions. We obtain fair agreement with experimental data and provide an explanation on why the recent experiment on $J/ψ\to η' h_1(1380), h_1(1380) \to K^{*+} K^- +c.c.$ observed in the $K^+ K^- π^0$ mode observes the peak of the $h_1(1380)$ at a higher energy than its nominal mass.

hep-ph↗

arXiv2018

$\boldsymbolη$-$\boldsymbol{^4{\rm He}}$ interaction from the $\boldsymbol{d d \to η^4{\rm He}}$ reaction near threshold

We analyze the data on the total cross sections for the $dd \to η^4{\rm He}$ reaction close to threshold and look for possible $η^4 {\rm He}$ bound states. We develop a framework in which the $η^4{\rm He}$ optical potential is the key ingredient, rather than parameterizing the scattering matrix, as is usually done. The strength of this potential, together with some production parameters, are fitted to the available experimental data. The relationship of the scattering matrix to the optical potential is established using the Bethe-Salpeter equation and the $η^4{\rm He}$ loop function incorporates the range of the interaction given by the experimental $^4 {\rm He}$ density. However, when we look for poles of the scattering matrix, we get poles in the bound region, poles in the positive energy region or no poles at all. If we further restrict the results with constraints from a theoretical model with all its uncertainties the bound states are not allowed. However, we find a bump structure in $|T|^2$ of the $η^4{\rm He} \to η^4{\rm He}$ amplitude below threshold for the remaining solutions.

nucl-th↗

arXiv2018

Pseudoscalar or vector meson production in non-leptonic decays of heavy hadrons

We have addressed the study of non-leptonic weak decays of heavy hadrons ($Λ_b, Λ_c, B$ and $D$), with external and internal emission to give two final hadrons, taking into account the spin-angular momentum structure of the mesons and baryons produced. A detailed angular momentum formulation is developed which leads to easy final formulas. By means of them we have made predictions for a large amount of reactions, up to a global factor, common to many of them, that we take from some particular data. Comparing the theoretical predictions with the experimental data, the agreement found is quite good in general and the discrepancies should give valuable information on intrinsic form factors, independent of the spin structure studied here. The formulas obtained are also useful in order to evaluate meson-meson or meson-baryon loops, for instance of $B$ decays, in which one has PP, PV, VP or VV intermediate states, with P for pseudoscalar mesons and V for vector meson and lay the grounds for studies of decays into three final particles.

hep-ph↗

arXiv2018

Dynamical Hadrons

In this talk I briefly review the theory of resonances dynamically generated from hadron-hadron scattering, sometimes referred to as "molecules"S. I give some classical examples of meson-meson and meson-baryon systems, as well as a few examples of different approaches to describe the interaction between hadrons. To conclude, I comment on a few recent works that suggest that some of the five new narrow $Ω_c$ states, recently discovered by the LHCb collaboration, can be interpreted as meson-baryon molecules.

hep-ph↗

arXiv2018

Molecular $Ω_b$ states

Motivated by the recent finding of five $Ω_c$ states by the LHCb collaboration, and the successful reproduction of three of them in a recent approach searching for molecular states of meson-baryon with the quantum numbers of $Ω_c$, we extend these ideas and make predictions for the interaction of meson-baryon in the beauty sector, searching for poles in the scattering matrix that correspond to physical states. We find several $Ω_b$ states: two states with masses 6405~MeV and 6465~MeV for $J^P= \frac{1}{2}^-$; two more states with masses 6427~MeV and 6665~MeV for $\frac{3}{2}^-$; and three states between 6500 and 6820~MeV, degenerate with $J^P=\frac{1}{2}^-,\,\frac{3}{2}^-$, stemming from the interaction of vector-baryon in the beauty sector.

hep-ph↗