arXiv subjects

W. H. Liang

Publications and source records attributed to W. H. Liang.

16 recordsLinked to original sources

arXiv2024

Triangle singularity in the $J/ψ\to ϕπ^+ a_0^-(π^- η),\; ϕπ^- a_0^+(π^+ η)$ decays

We study the $J/ψ\to ϕπ^+ a_0(980)^- (a_0^- \to π^- η)$ decay, evaluating the double mass distribution in terms of the $π^- η$ and $π^+ a^-_0$ invariant masses. We show that the $π^- η$ mass distribution exhibits the typical cusp structure of the $a_0(980)$ seen in recent high statistics experiments, and the $π^+ a^-_0$ spectrum shows clearly a peak around $M_{\rm inv}(π^+ a^-_0)=1420 \,{\rm MeV}$, corresponding to a triangle singularity. When integrating over the two invariant masses we find a branching ratio for this decay of the order of $10^{-5}$, which is easily accessible in present laboratories. We also call attention to the fact that the signal obtained is compatible with a bump experimentally observed in the $ηπ^+π^-$ mass distribution in the $J/ψ\to ϕηπ^+π^-$ decay and encourage further analysis to extract from there the $ϕπ^+ a_0^-$ and $ϕπ^- a_0^+$ decay modes.

hep-ph↗

arXiv2021

$D^0 D^0 π^+$ mass distribution in the production of the $T_{cc}$ exotic state

We perform a unitary coupled channel study of the interaction of the $D^{*+} D^0, D^{*0} D^+$ channels and find a state barely bound, very close to isospin $I=0$. We take the experimental mass as input and obtain the width of the state and the $D^0 D^0 π^+$ mass distribution. When the mass of the $T_{cc}$ state quoted in the experimental paper from raw data is used, the width obtained is of the order of the $80 \;{\rm keV}$, small compared to the value given in that work. Yet, when the mass obtained in an analysis of the data considering the experimental resolution is taken, the width obtained is about $43 \;{\rm keV}$ and both the width and the $D^0 D^0 π^+$ mass distribution are in remarkable agreement with the results obtained in that latter analysis.

hep-ph↗

arXiv2021

The $πf_0(500)$ decay of the $a_1(1260)$

We evaluate the $a_1(1260) \to πσ(f_0(500))$ decay width from the perspective that the $a_1(1260)$ resonance is dynamically generated from the pseudoscalar-vector interaction and the $σ$ arises from the pseudoscalar-pseudoscalar interaction. A triangle mechanism with $a_1(1260) \to ρπ$ followed by $ρ\to ππ$ and a fusion of two pions within the loop to produce the $σ$ provides the mechanism for this decay under these assumptions for the nature of the two resonances. We obtain widths of the order of $13-22$ MeV. Present experimental results differ substantially from each other, suggesting that extra efforts should be devoted to the precise extraction of this important partial decay width, which should provide valuable information on the nature of the axial vector and scalar meson resonances and help clarify the role of the $πσ$ channel in recent lattice QCD calculations of the $a_1$.

hep-ph↗

arXiv2021

Inconsistency of the data on the $K_1(1270) \to πK^*_0(1430)$ decay width

We show, using the same Lagrangian for the $K_1(1270) \to πK^*_0(1430)$ and $K^*_0(1430) \to K_1(1270) π$ decays, that the present PDG data on the partial decay width of $K_1(1270) \to πK^*_0(1430)$ implies a width for $K^*_0(1430) \to K_1(1270) π$ decay which is about ten times larger than the total $K^*_0(1430)$ width. A discussion on this inconsistency is done, stressing its relationship to the existence of two $K_1(1270)$ states obtained with the chiral unitary theory, which are not considered in the experimental analyses of $Kππ$ data.

hep-ph↗

arXiv2019

Line shape and $D^{(\ast)}\bar D^{(\ast)}$ probabilities of $ψ(3770)$ from the $e^+e^-\to D\bar D$ reaction

We have performed a calculation of the $D\bar D$, $D\bar D^\ast$, $D^\ast\bar D$, $D^\ast\bar D^\ast$ components in the wave function of the $ψ(3770)$. For this we make use of the $^3P_0$ model to find the coupling of $ψ(3770)$ to these components, that with an elaborate angular momentum algebra can be obtained with only one parameter. Then we use data for the $e^+e^-\to D\bar D$ reaction, from where we determine a form factor needed in the theoretical frame work, as well as other parameters needed to evaluate the meson-meson selfenergy of the $ψ(3770)$. Once this is done we determine the $Z$ probability to still have a vector core and the probability to have the different meson components. We find $Z$ about $80\sim85\%$, and the individual meson-meson components are rather small, providing new empirical information to support the largely $q\bar q$ component of vector mesons, and the $ψ(3770)$ in particular.

hep-ph↗

arXiv2018

Molecular $Ω_c$ states generated from coupled meson-baryon channels

We have investigated $Ω_c$ states that are dynamically generated from the meson-baryon interaction. We use an extension of the local hidden gauge to obtain the interaction from the exchange of vector mesons. We show that the dominant terms come from the exchange of light vectors, where the heavy quarks are spectators. This has as a consequence that heavy quark symmetry is preserved for the dominant terms in the $(1/m_Q)$ counting, and also that the interaction in this case can be obtained from the $\textrm{SU(3)}$ chiral Lagrangians. We show that for a standard value for the cutoff regulating the loop, we obtain two states with $J^{P}={1/2}^{-}$ and two more with $J^{P}={3/2}^{-}$, three of them in remarkable agreement with three experimental states in mass and width. We also make predictions at higher energies for states of vector-baryon nature.

hep-ph↗

arXiv2017

Abnormal isospin violation and $a_0 -f_0$ mixing in the $D_s^+ \to π^+ π^0 a_0(980) (f_0(980))$ reactions

We have chosen the reactions $D_s^+ \to π^+ π^0 a_0(980) (f_0(980))$ investigating the isospin violating channel $D_s^+ \to π^+ π^0 f_0(980)$. The reaction was chosen because by varying the $π^0 a_0(980) (f_0(980))$ invariant mass one goes through the peak of a triangle singularity emerging from $D_s^+ \to π^+\bar K^* K$, followed by $\bar K^* \to \bar K π^0$ and the further merging of $K \bar K$ to produce the $a_0(980)$ or $f_0(980)$. We found that the amount of isospin violation had its peak precisely at the value of the $π^0 a_0(980) (f_0(980))$ invariant mass where the singularity has its maximum, stressing the role of the triangle singularities as a factor to enhance the mixing of the $f_0(980)$ and $a_0(980)$ resonances. We calculate absolute rates for the reactions and show that they are within present measurable range. The measurement of these reactions would bring further information into the role of triangle singularities in isospin violation and the $a_0 -f_0$ mixing in particular and shed further light into the nature of the low energy scalar mesons.

hep-ph↗

arXiv2017

Predictions for $Ξ_b^- \rightarrow π^- \left(D_s^- \right) \ Ξ_c^0 (2790) \left(Ξ_c^0 (2815) \right)$ and $Ξ_b^- \rightarrow \barν_l l \ Ξ_c^0 (2790) \left(Ξ_c^0 (2815) \right)$

We have performed the calculations for the nonleptonic $Ξ_b^- \rightarrow π^- \ Ξ_c^0 (2790) \left(J=\frac{1}{2}\right)$ and $Ξ_b^- \rightarrow π^- \ Ξ_c^0 (2815) \left(J=\frac{3}{2}\right)$ and the same reactions replacing the $π^-$ by a $D_s^-$. At the same time we evaluate the semileptonic rates for $Ξ_b^- \rightarrow \barν_l l \ Ξ_c^0 (2790)$ and $Ξ_b^- \rightarrow \barν_l l \ Ξ_c^0 (2815)$. We look at the reactions from the perspective that the $Ξ_c^0 (2790)$ and $Ξ_c^0 (2815)$ resonances are dynamically generated from the pseudoscalar-baryon and vector-baryon interactions. We evaluate ratios of the rates of these reactions and make predictions that can be tested in future experiments. We also find that the results are rather sensitive to the coupling of the $Ξ_c^*$ resonances to the $D^* Σ$ and $D^* Λ$ components.

hep-ph↗

arXiv2015

Two, three, many body systems involving mesons. Multimeson condensates

In this talk we review results from studies with unconventional many hadron systems containing mesons: systems with two mesons and one baryon, three mesons, some novel systems with two baryons and one meson, and finally systems with many vector mesons, up to six, with their spins aligned forming states of increasing spin. We show that in many cases one has experimental counterparts for the states found, while in some other cases they remain as predictions, which we suggest to be searched in BESIII, Belle, LHCb, FAIR and other facilities.

hep-ph↗

arXiv2015

Baryon states with open charm in the extended local hidden gauge approach

In this paper we examine the interaction of $D N$ and $D^* N$ states, together with their coupled channels, by using an extension of the local hidden gauge formalism from the light meson sector, which is based on heavy quark spin symmetry. The scheme is based on the use of the impulse approximation at the quark level, with the heavy quarks acting as spectators, which occurs for the dominant terms where there is the exchange of a light meson. The pion exchange and the Weinberg-Tomozawa interactions are generalized and with this dynamics we look for states generated from the interaction, with a unitary coupled channels approach that mixes the pseudoscalar-baryon and vector-baryon states. We find two states with nearly zero width which are associated to the $Λ_c(2595)$ and $Λ_c(2625)$. The lower state, with $J^P = 1/2^-$, couples to $D N$ and $D^* N$, and the second one, with $J^P = 3/2^-$, to $D^* N$. In addition to these two $Λ_c$ states, we find four more states with $I=0$, one of them nearly degenerate in two states of $J=1/2,\ 3/2$. Furthermore we find three states in $I=1$, two of them degenerate in $J=1/2, 3/2$.

hep-ph↗

arXiv2014

$B^0$ and $B^0_s$ decays into $J/ψ$ plus a scalar or vector meson

We extend a recent approach to describe the $B^0$ and $B^0_s$ decays into $J/ψ$ $f_0(500)$ and $J/ψ$ $f_0(980)$, relating it to the $B^0$ and $B^0_s$ decays into $J/ψ$ and a vector meson, $ϕ$, $ρ$, $K^*$. In addition the $B^0$ and $B^0_s$ decays into $J/ψ$ and $κ(800)$ are evaluated and compared to the $K^*$ vector production. The rates obtained are in agreement with available experiment while predictions are made for the $J/ψ$ plus $κ(800)$ decay.

hep-ph↗

arXiv2014

Signature of an $h_1$ state from $J/ψ\to ηK^{0}\bar{K}^{0}$ and theoretical description of the $Z_c(3900)$ and $Z_c(4020)$ as $D \bar D^$ and $D^ \bar D^*$ molecular states

In this talk we address two topics: The first one is an empirical explanation in terms of a new state $h_1$ of the peak in the $K^{*0}\bar{K}^{*0}$ invariant mass distribution close to threshold of this channel in the $J/ψ\to ηK^{*0}\bar{K}^{*0}$ decay. The second one is a theoretical description of the isospin $I=1$ $Z_c(3900)$ and $Z_c(4020)$ states in terms of molecular states of $D \bar D^*+ cc$ and $D^* \bar D^*$.

hep-ph↗

arXiv2014

$B^0$ and $B^0_s$ decays into $J/ψ$ $f_0(980)$ and $J/ψ$ $f_0(500)$ and the nature of the scalar resonances

We describe the $B^0$ and $B^0_s$ decays into $J/ψ$ $f_0(500)$ and $J/ψ$ $f_0(980)$ by taking into account the dominant process for the weak decay of $B^0$ and $B^0_s$ into $J/ψ$ and a $q \bar q$ component. After hadronization of this $q \bar q$ component into pairs of pseudoscalar mesons we obtain certain weights for the meson-meson components and allow them to interact among themselves. The final state interaction of the meson-meson components, described in terms of chiral unitary theory, gives rise to the $f_0(980)$ and $f_0(500)$ resonances and we can obtain the $π^+ π^- $ invariant mass distributions after the decay of the resonances, which allows us to compare directly to the experiments. We obtain ratios of $J/ψ$ $f_0(980)$ and $J/ψ$ $f_0(500)$ for each of the $B$ decays in quantitative agreement with experiment, with the $f_0(980)$ clearly dominant in the $B^0_s$ decay and the $f_0(500)$ in the $B^0$ decay.

hep-ph↗

arXiv2014

Baryon states with open beauty in the extended local hidden gauge approach

In this paper we examine the interaction of \bar B N, \bar B Δ, \bar B^* N and \bar B^* Δstates, together with their coupled channels, using a mapping from the light meson sector. The assumption that the heavy quarks act as spectators at the quark level automatically leads us to the results of the heavy quark spin symmetry for pion exchange and reproduces the results of the Weinberg Tomozawa term, coming from light vector exchanges in the extended local hidden gauge approach. With this dynamics we look for states dynamically generated from the interaction and find two states with nearly zero width, which we associate to the Λ_b(5912) and Λ_b(5920) states. The states couple mostly to \bar B^* N, which are degenerate with the Weinberg Tomozawa interaction. The difference of masses between these two states, with J=1/2, 3/2 respectively, is due to pion exchange connecting these states to intermediate \bar B N states. In addition to these two Λ_b states, we find three more states with I=0, one of them nearly degenerate in two states of J=1/2,3/2. Furthermore we also find eight more states in $I=1$, two of them degenerate in J=1/2, 3/2, and other two degenerate in J=1/2, 3/2, 5/2.

hep-ph↗

arXiv2013

Description of $ρ(1700)$ as a $ρK \bar{K}$ system with the fixed center approximation

We study the $ρK\bar{K}$ system with an aim to describe the $ρ(1700)$ resonance. The chiral unitary approach has achieved success in a description of systems of the light hadron sector. With this method, the $K \bar{K}$ system in the isospin sector $I=0$, is found to be a dominant component of the $f_0 (980)$ resonance. Therefore, by regarding the $K\bar{K}$ system as a cluster, the $f_0 (980)$ resonance, we evaluate the $ρK\bar{K}$ system applying the fixed center approximation to the Faddeev equations. We construct the $ρK$ unitarized amplitude using the chiral unitary approach. As a result, we find a peak in the three-body amplitude around 1739 MeV and a width of about 227 MeV. The effect of the width of $ρ$ and $f_0 (980)$ is also discussed. We associate this peak to the $ρ(1700)$ which has a mass of $1720 \pm 20$ MeV and a width of $250 \pm 100$ MeV.

hep-ph↗

arXiv2012

Isospin breaking and $f_0(980)$-$a_0(980)$ mixing in the $η(1405) \to π^{0} f_0(980)$ reaction

We make a theoretical study of the $η(1405) \to π^{0} f_0(980)$ and $η(1405) \to π^{0} a_0(980)$ reactions with an aim to determine the isospin violation and the mixing of the $f_0(980)$ and $a_0(980)$ resonances. We make use of the chiral unitary approach where these two resonances appear as composite states of two mesons, dynamically generated by the meson-meson interaction provided by chiral Lagrangians. We obtain a very narrow shape for the $f_0(980)$ production in agreement with a BES experiment. As to the amount of isospin violation, or $f_0(980)$ and $a_0(980)$ mixing, assuming constant vertices for the primary $η(1405)\rightarrow π^{0}K\bar{K}$ and $η(1405)\rightarrow π^{0}π^{0}η$ production, we find results which are much smaller than found in the recent experimental BES paper, but consistent with results found in two other related BES experiments. We have tried to understand this anomaly by assuming an I=1 mixture in the $η(1405)$ wave function, but this leads to a much bigger width of the $f_0(980)$ mass distribution than observed experimentally. The problem is solved by using the primary production driven by $η' \to K^* \bar K$ followed by $K^* \to K π$, which induces an extra singularity in the loop functions needed to produce the $f_0(980)$ and $a_0(980)$ resonances. Improving upon earlier work along the same lines, and using the chiral unitary approach, we can now predict absolute values for the ratio $Γ(π^0, π^+ π^-)/Γ(π^0, π^0 η)$ which are in fair agreement with experiment. We also show that the same results hold if we had the $η(1475)$ resonance or a mixture of these two states, as seems to be the case in the BES experiment.

hep-ph↗