Search

In the past two decades, one of the most puzzling phenomena discovered in hadron physics is that a nominal hadronic state can actually correspond to two poles on the complex energy plane. This phenomenon was first noticed for the $\Lambda(1405)$, and then for $K_1(1270)$ and to a less extent for $D_0^*(2300)$. In this Letter, we show explicitly how the two-pole structures emerge from the underlying chiral dynamics describing the coupled-channel interactions between heavy matter particles and Nambu-Goldstone bosons. In particular, the fact that two poles appear between the two dominant coupled channels can be attributed to the particular form of the leading order chiral potentials of the Weinberg-Tomozawa form. Their lineshapes overlap with each other because the degeneracy of the two coupled channels is only broken by explicit chiral symmetry breaking of higher order. We predict that for light-quark~(pion) masses heavier than their physical values, the two-pole structures disappear, which can be easily verified by future lattice QCD simulations. Furthermore, we anticipate similar two-pole structures in other systems, such as the isopin $1/2$ $\bar{K}\Sigma_c-\pi\Xi'_c$ coupled channel, which await for experimental discoveries., Comment: 5 pages, 4 figures

In hadron spectrum physics, the partial wave analysis is a primary method used to extract properties of hadronic resonances. The covariant orbital-spin coupling scheme holds unique advantages over other partial wave methods due to its Lorentz covariant form and determined orbital-spin quantum numbers. This paper presents a general form of the covariant orbital-spin coupling scheme based on the irreducible tensor of the homogeneous proper Lorentz group and its little groups. A systematic procedure for constructing partial wave amplitude in a Lorentz covariant way is provided, which can be applied to both massive and massless particles. Specific examples are also included., Comment: 38 pages and 2 figures

We propose a chiral quark model including the $\omega$ and $\rho$ meson contributions in addition to the $\pi$ and $\sigma$ meson contributions. We show that the masses of the ground state baryons such as the nucleon, $\Lambda_c$ and $\Lambda_b$ are dramatically improved in the model with the vector mesons compared with the one without them. The study of the tetraquark $T_{cc}$ is also performed in a coupled channel calculation and the resultant mass is much closer to its experimental value than the result without vector meson contribution. This approach can be applied to the future study of multi-quark systems., Comment: 6 pages, 4 figures

Based on the high statistical data of the CLAS Collaboration on $γp \to ϕp$ reaction in the center-of-mass energy range of 2.2 GeV to 2.8 GeV, we investigate the possible existence of strange molecular partners of $P_c$ states, i.e., $N^*(2080)$ and $N^*(2270)$ as $K^*Σ$ and $K^*Σ^*$ molecular states. In addition to the t-channel Pomeron exchange, t-channel meson exchange including pseudo-scalar meson $(π,η)$, scalar meson $(σ, a_0(980), f_0(980))$, axial-vector meson $f_1(1285)$, tensor meson $f_2(1270)$, as well as s- and u-channel proton exchange, including s-channel $N^*(2080)$ and $N^*(2270)$ states can fit the data very well. The fitted coupling constants of these $N^*$ molecular states to $pϕ$ and $γp$ are consistent with the results directly calculated from the relevant hadronic triangle diagrams of the molecular picture., 17 pages, 9 figures, 4 tables

The possible hadronic molecules in $D_s^{(*)+}Ξ_c^{(',*)}$ systems with $J^P=1/2^-,3/2^-$ and $5/2^-$ are investigated with interactions described by light meson exchanges. By varying the cutoff in a phenomenologically reasonable range of $1\sim2.5$ GeV, we find ten near-threshold (bound or virtual) states in the single-channel case. After introducing the coupled-channel dynamics of $D_s^{+}Ξ_c$-$D_s^{+}Ξ_c^{'}$-$D_s^{*+}Ξ_c$-$D_s^{+}Ξ_c^{*}$-$D_s^{*+}Ξ_c^{'}$-$D_s^{*+}Ξ_c^{*}$ systems, these states, except those below the lowest channels in each $J^{P}$ sector, move into the complex energy plane and become resonances in the mass range of $4.43\sim4.76$ GeV. Their spin-parities and nearby thresholds are $1/2^-(D_s^{+}Ξ_c)$, $1/2^-(D_s^{+}Ξ_c^{'})$, $1/2^-(D_s^{*+}Ξ_c)$,$1/2^-(D_s^{*+}Ξ_c^{'})$, $1/2^-(D_s^{*+}Ξ_c^{*})$ , $3/2^-(D_s^{*+}Ξ_c)$, $3/2^-(D_s^{+}Ξ_c)$, $3/2^-(D_s^{*+}Ξ_c^{'})$, $3/2^-(D_s^{*+}Ξ_c^{*})$, and $5/2^-(D_s^{*+}Ξ_c^{*})$. The impacts of the $δ(r)$-term in the one-boson-exchange model on these states are presented. Setting $Λ=1.5$ GeV as an illustrative value, it is found that $1/2^-(D_s^{+}Ξ_c)$ is a stable bound state (becoming unstable if turning on the coupling to lower channels), $1/2^-(D_s^{*+}Ξ_c)$ and $3/2^-(D_s^{*+}Ξ_c)$ are physical resonances in both cases of including or excluding the $δ(r)$-term, while the other seven states are physical resonances or ``virtual-state-like" poles near thresholds, depending on including the $δ(r)$-term or not. In addition, the partial decay widths of the physical resonances are provided. These double-charm hidden-strangeness pentaquark states, as the partners of experimentally observed $P_c$ and $P_{cs}$ states, can be searched for in the $D^{(*)}Λ_c$ final states in future., 15 pages, 6 figures, 9 tables

In our previous work, the available differential cross-section data for $γp\to K^{\ast +}Σ^0$ and $γp \to K^{\ast 0}Σ^+$ have been analyzed within an effective Lagrangian approach. It was found that one needs to introduce the $s$-channel $Δ(1905){5/2}^+$ resonance exchange besides the $t$-channel $K$, $κ$, and $K^\ast$ exchanges, the $s$-channel $N$ and $Δ$ exchanges, the $u$-channel $Λ$, $Σ$, and $Σ^\ast$ exchanges, and the generalized contact term in constructing the reaction amplitudes to describe the data. In the present work, we re-analyze the available data for $γp\to K^{\ast +}Σ^0$ and $γp \to K^{\ast 0}Σ^+$ by replacing the $Δ(1905){5/2}^+$ resonance in our previous work with the $N(2080){3/2}^-$ state which was proposed to be a $K^\ast Σ$ molecule as the strange partner of the $P_c^+(4457)$ hadronic molecular state. It turns out that in the near-threshold energy region, the available data can be well reproduced, indicating that the molecular structure of the $N(2080){3/2}^-$ state is compatible with the available cross-section data of $K^\astΣ$ photoproduction reactions. Further analysis shows that the $N(2080){3/2}^-$ exchange provides dominant contributions to the cross-sections of $γp\to K^{\ast +}Σ^0$, and significant contributions to the cross-sections of both $γp\to K^{\ast +}Σ^0$ and $γp \to K^{\ast 0}Σ^+$ reactions are also found from the $N$ and $Δ$ exchanges. Predictions of the beam asymmetry $Σ$, target asymmetry $T$, and recoil baryon asymmetry $P$ are presented and compared with those from our previous work. Measurements of the data on these observables are called on to further constrain the reaction mechanisms of $K^\astΣ$ photoproduction reactions and to verify the molecular scenario of the $N(2080){3/2}^-$ state., 8 pages, 6 figures

We propose that the $X(3915)$ observed in the $J/\psi\,\omega$ channel is the same state as the $\chi_{c2}(3930)$, and the $X(3960)$, observed in the $D_s^+D_s^-$ channel, is an $S$-wave $D_s^+ D_s^-$ hadronic molecule. In addition, the $J^{PC}=0^{++}$ {component in the $B^+\to D^+D^-K^+$} assigned to the $X(3915)$ in the current {\it Review of Particle Physics} has the same origin as the $X(3960)$, which has a mass around 3.94~GeV. To check the proposal, the available data in the $D\bar D$ and $D_s^+ D_s^-$ channels from both $ B$ decays and $\gamma\gamma$ fusion reaction are analyzed considering both the $D\bar D$-$D_s\bar D_s$-$D^*\bar D^*$-$D_s^*\bar D_s^*$ coupled channels with $0^{++}$ and a $2^{++}$ state introduced additionally. It is found that all the data in different processes can be simultaneously well reproduced, and the coupled-channel dynamics produce four hidden-charm scalar molecular states with masses around 3.73, 3.94, 3.99 and 4.23~GeV, respectively. The results may deepen our understanding of the spectrum of charmonia as well as of the interactions between charmed hadrons., Comment: 15 pages, 6 figures, 2 tables, to apear in Sci. Bull

An exotic state with $J^{PC}=1^{-+}$, denoted by $η_1(1855)$, was observed by BESIII collaboration recently in $J/ψ\to γηη'$. The fact that its mass is just below the threshold of $K\bar K_1(1400)$ stimulates us to investigate whether this exotic state can be interpreted as a $K\bar K_1(1400)+$ c.c { molecule or not}. Using the one boson exchange model, we show that it is possible for $K\bar K_1(1400)$ with $J^{PC}=1^{-+}$ to bind together by taking the momentum cutoff $Λ\gtrsim 2$ GeV and yield the same binding energy as the experimental value when $Λ\approx 2.5$ GeV. In this molecular picture, the predicted branch ratio $\mathrm{Br}(η_1(1855)\toηη') \approx 15\%$ is consistent with the experimental results, which again supports the molecular explanation of $η_1(1855)$. Relevant systems, namely $K\bar K_1(1400)$ with $J^{PC}=1^{--}$ and $K\bar K_1(1270)$ with $J^{PC}=1^{-\pm}$, are also investigated, some of which can be searched for in the future experiments., 7 pages, 5 figures

Lots of charmonium-like structures have been observed in the last two decades. Most of them have quantum numbers that can be formed by a pair of charm and anticharm quarks, thus it is difficult to unambiguously identify the exotic ones among them. In this Letter, by exploiting heavy quark spin symmetry, we present a robust prediction of the hadronic molecular scenario, where the $\psi(4230),\psi(4360)$ and $\psi(4415)$ are identified as $D\bar D_1,D^*\bar D_1$ and $D^*\bar D^*_2$ bound states, respectively. We show that a flavor-neutral charmonium-like exotic state with quantum numbers $J^{PC}=0^{--}$, denoted as $\psi_0(4360)$, should exist as a $D^*\bar D_1$ bound state. The mass and width of the $\psi_0(4360)$} are predicted to be $(4366\pm18)$ MeV and less than 10 MeV, respectively. The $\psi_0(4360)$ is significant in two folds: no $0^{--}$ hadron has been observed so far, and a study of this state will enlighten the understanding of the mysterious vector mesons between 4.2 and 4.5 GeV, as well as the nature of previously observed exotic $Z_c$ and $P_c$ states. We propose that such an exotic state can be searched for in $e^+e^-\to \eta \psi_0(4360)$ and uniquely identified by measuring the angular distribution of the outgoing $\eta$ meson., Comment: 7+3 pages, 7 figures, 2 tables; version to be appeared in PRL

We study dynamically generated $a_0$ resonances by interactions between vector mesons including their coupling to channels of pseudoscalar mesons within coupled-channel approach. Both vector and pseudoscalar mesons are considered as $t$-channel exchanged mesons for calculating interactions between vector mesons. Analogous to $a_0(980)$ as a $K\bar K-\pi\eta$ dynamically generated state, there is an $a_0(1710)$ as a coupled channel dynamically generated state near $K^*\bar{K}^*$ threshold. The channels involved are $\rho\phi,K^*\bar{K}^*,\rho\omega, K\bar{K},\pi\eta$. This $a_0$ mainly decays to $\rho\omega$, $\pi\eta$ and $K\bar{K}$. This pole is much tied to the coupled channel effect. If we turn off either $\rho\phi$ or $K^*\bar{K}^*$, the pole disappears. In addition, it is found that $a_0(1450)$ may also be dynamically generated by $\rho\omega$ interactions due to $\pi$ and $\eta$ exchange., Comment: arXiv admin note: substantial text overlap with arXiv:2107.14470

The $f_0(1710)$ was previously proposed to be dynamically generated state by interactions between vector mesons. We extend the study of $f_0(1710)$ by including its coupling to channels of pseudoscalar mesons within coupled-channel approach. The channels involved are $K^*\bar{K}^*,\rho\rho,\omega\omega,\phi\phi, \omega\phi,\pi\pi,K\bar{K},\eta\eta$. We show that the pole assigned to $f_0(1710)$ does not change much. Then we calculate the partial decay widths of $f_0(1710) \to K^*\bar{K}^* \to \pi\pi,K\bar{K},\eta\eta$ as the coupled channel dynamically generated state as well as assuming it to be pure $K^*\bar{K}^*$ molecule. In both cases the ratios of partial decay widths agree fairly with that in PDG.

By using the covariant L-S Scheme for the partial wave analysis, we deduce the ratios between the S-wave and D-wave contributions from the recent data of $��(1^-) \to B_8(1/2^+) \bar{B}_8(1/2^-)$ from the BESIII collaboration. For the $J/��\to ��\bar��$ and $J/��(��(2S))\to ��^{+}\bar��^{-}$, the ratios are fixed and the average angular momenta are computed to estimate the effective radii of these processes. The results show that the effective radii of these decays of $J/��(��(2S))$ are very small, which are around 0.04 fm. Thus, it is a nice place to search excited baryon resonances with lower spin in the decays of $J/��(��(2S))$. Furthermore, for the other $��(1^-) \to B_8(1/2^+) \bar{B}_8(1/2^-)$ reactions, we propose some methods to get such effective radius.

In a recent measurement LHCb reported pronounced structures in the $J/��J/��$ spectrum. One of the various possible explanations of those is that they emerge from non-perturbative interactions of vector charmonia. It is thus important to understand whether it is possible to form a bound state of two charmonia interacting through the exchange of gluons, which hadronise into two pions at the longest distance. In this paper, we demonstrate that, given our current understanding of hadron-hadron interactions, the exchange of correlated light mesons (pions and kaons) is able to provide sizeable attraction to the di-$J/��$ system, and it is possible for two $J/��$ mesons to form a bound state. As a side result we find from an analysis of the data for the $��(2S)\to J/������$ transition including both $����$ and $K\bar K$ final state interactions an improved value for the $��(2S)\to J/��$ transition chromo-electric polarisability: $|��_{��(2S)J/��}|= (1.8\pm 0.1)~\mbox{GeV}^{-3}$, where the uncertainty also includes the one induced by the final state interactions., 11 pages, 7 figures, version to appear in Sci. Bull

Many efforts have been made to reveal the nature of the overabundant resonant structures observed by the worldwide experiments in the last two decades. Hadronic molecules attract special attention because many of these seemingly unconventional resonances are located close to the threshold of a pair of hadrons. To give an overall feature of the spectrum of hadronic molecules composed of a pair of heavy-antiheavy hadrons, namely, which pairs are possible to form molecular states, we take charmed hadrons for example to investigate the interaction between them and search for poles by solving the Bethe-Salpeter equation. We consider all possible combinations of hadron pairs of the $S$-wave singly-charmed mesons and baryons as well as the narrow $P$-wave charmed mesons. The interactions, which are assumed to be meson-exchange saturated, are described by constant contact terms which are resummed to generate poles. It turns out that if a system is attractive near threshold by the light meson exchange, there is a pole close to threshold corresponding to a bound state or a virtual state, depending on the strength of interaction and the cutoff. In total, 229 molecular states are predicted. The observed near-threshold structures with hidden-charm, like the famous $X(3872)$ and $P_c$ states, fit into the spectrum we obtain. We also highlight a $\Lambda_c\bar \Lambda_c$ bound state that has a pole consistent with the cross section of the $e^+e^-\to\Lambda_c\bar \Lambda_c$ precisely measured by the BESIII Collaboration., Comment: Typos of the loop integral, Eq.53, corrected

The effects of the $��_c\bar{D}^*$-$��_{c}(2595)\bar{D}$ coupled-channel dynamics and various one-boson-exchange (OBE) forces for the LHCb pentaquark states, $P_c(4440)$ and $P_c(4457)$, are reinvestigated. Both the pion and $��$-meson exchanges are considered for the $��_c\bar{D}^*$-$��_{c}(2595)\bar{D}$ coupled-channel dynamics. It is found that the role of the $��_{c}(2595)\bar{D}$ channel in the descriptions of the $P_c(4440)$ and $P_c(4457)$ states is not significant with the OBE parameters constrained by other experimental sources. The naive OBE models with the short-distance $��(\vec{r})$ term of the one-pion exchange (OPE) keep failing to reproduce the $P_c(4440)$ and $P_c(4457)$ states simultaneously. The OPE potential with the full $��(\vec{r})$ term results in a too large mass splitting for the $J^P=1/2^-$ and $3/2^-$ $��_c\bar{D}^*$ bound states with total isospin $I=1/2$. The OBE model with only the OPE $��(\vec{r})$ term dropped may fit the splitting much better but somewhat underestimates the splitting. Since the $��(\vec r)$ potential is from short-distance physics, which also contains contributions from the exchange of mesons heavier than those considered explicitly, we vary the strength of the $��(\vec r)$ potential and find that the masses of the $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ can be reproduced simultaneously with the $��(\vec r)$ term in the OBE model reduced by about 80\%. While two different spin assignments are possible to produce their masses, in the preferred description, the spin parities of the $P_c(4440)$ and $P_c(4457)$ are $3/2^-$ and $1/2^-$, respectively., 34 pages, 6 figures, 8 tables

The possibility of the Y(4260) being the molecular state of $D\bar D_1(2420)+\mathrm{c.c.}$ is investigated in the one boson exchange model. It turns out that the potential of $J^{PC}=1^{--}$ state formed by $D\bar D_1(2420)+\mathrm{c.c.}$ is attractive and strong enough to bind them together when the momentum cutoff $\Lambda \gtrsim 1.4$ GeV. To produce the Y(4260) with correct binding energy, we need $\Lambda\approx 2.1$ GeV. Besides, $D\bar D_1(2420)+\mathrm{c.c.}$ can also form a state with exotic quantum numbers, $J^{PC}=1^{-+}$, and its potential similar with that of the $J^{PC}=1^{--}$ state. Therefore, an exotic state with mass around 4240 MeV (called $\eta_{c1}(4240)$) is predicted to exist. Our estimation of the mass of the $J^{PC}=1^{-+}$ state in charmonium region is in agreement with those predicted by the chiral quark model and the lattice QCD. The possible decay modes and their relative widths are estimated and the results suggest that this exotic state can be searched for in $\eta\eta_c$ and $\eta\chi_{c1}$ channels., Comment: 11 pages, 5 figures, some errors corrected

Up to now, all charge radius measurements of the proton and deuteron assumed uniform spheroidal charge distribution. We investigate the nuclear deformation effects on these charge radius measurements by assuming a uniform prolate charge distribution for the proton and deuteron. We solve the energy levels of the corresponding muonic and electric atoms with such deformed nucleus and present how the purely quadruple deformation of proton and deuteron affects their Lamb shifts. The numerical results suggest that the deformation of proton and deuteron leads to that the charge radius extracted from the electronic measurement should be smaller than the corresponding one in the muonic measurement which assumed uniform spheroidal charge distribution. If the central values of newest measurements for the proton are adopted, the proton would have a prolate structure with the 0.91 $\mathrm{fm}$ long axis and 0.73 $\mathrm{fm}$ short axis. Further improved precise charge radius measurements of the proton and deuteron will help us to pin down their shape deformation., Comment: 13pages, 4figures

The $����$ scattering has been studied by two groups which both claimed a dynamical generated scalar meson, most likely to be $f_0(1370)$. Here we investigate the influence of coupled-channels of pseudoscalar mesons, i.e., $����$ and $\bar KK$, on this dynamical generated scalar state. With the coupled channel effect included, the pole and partial decay widths are found to be more close to PDG values for $f_0(1500)$., 11 pages with 4 figures

In 2010, $��^*_{c\bar{c}}$ states were predicted as the strange number $S=-1$ partners of $N^*_{c\bar{c}}$, which are well known now as the $P_c$ states and observed experimentally by LHCb Collaboration. We analyze the decay behaviors of $��_{c\bar{c}}$ as S-wave hadronic molecules within the effective Lagrangian framework by a similar method, which has been applied on $P_c$ states successfully. With partial widths of possible decay channels calculated, we find that $��_{c\bar{c}}(4213)$ and $��_{c\bar{c}}(4403)$, which are formed as pseudoscalar meson baryon molecules, mainly decay to the $��_c ��$ channel. For the two vector meson baryon molecule states, our results show that the total decay width with $J^P=\frac12^-$ is by one order of magnitude larger than that with $J^P=\frac32^-$. The decay patterns and relative decay ratios are very different for $��_{c\bar{c}}(4370)$ being a $D_s^{* -} ��_c^+$ or $\bar{D}^{*} ��_c$ molecule state. The main decay channels of $��_{c\bar{c}}(4550)$ are $\bar{D}^{(*)} ��^{(*,\prime)}_c$ because of the pseudoscalar meson exchange mechanism. In addition, $\bar{D}^{*} ��_c$ is the dominant decay channel of $��_{c\bar{c}}(4490)$ which is assumed as a $\bar{D} ��_c^{*}$ bound state. These decay patterns of the $��^*_{c\bar{c}}$ states would provide a guidance for their future experimental searches and help us to understand their internal structures.

Up to now, the $N^*$ production from $e^+e^-$ annihilations has been studied only around charmonium region. Charmonium decays to $N^*$s are analogous to (time-like) EM form factors in that the charm quark annihilation provides a nearly pointlike (ggg) current. Complementary to other sources, such as $\pi N$, $eN$ and $\gamma N$ reactions, this new source for $N^*$ spectroscopy has a few advantages, such as an isospin filter and a low spin filter. The experimental results on $N^*$ from $e^+e^-$ annihilations and their phenomenological implications are reviewed. Possible new sources on $N^*$ production from $e^+e^-$ annihilations are discussed., Comment: 7 pages, 4 figures. Contribution to the proceedings of the 11th International Workshop on the Physics of Excited Nucleons, 20-23 August 2017, University of South Carolina, Columbia, SC, USA

Very recently, a new $��^{*}$ state was reported by the Belle Collaboration, with its mass of $2012.4 \pm 0.7\ \text{(stat)}\pm 0.6\ \text{(syst)}\ \mathrm{MeV}$, which locates just below the $K��^*$ threshold and hence hints to be a possible $K��^*$ hadronic molecule. Using the effective Lagrangian approach as the same as our previous works for other possible hadronic molecular states, we investigate the decay behavior of this new $��^*$ state within the hadronic molecular picture. The results show that the measured decay width can be reproduced well and its dominant decay channel is predicted to be the $K����$ three-body decay. This suggests that the newly observed $��^*$ may be ascribed as the $J^P={3/2}^-$ $K��^*$ hadronic molecular state and can be further checked through its $K����$ decay channel., 7pages, 6 figures

Invoked by the recent CMS observation regarding candidates of the $��_b(3P)$ multiplet, we analyze the ultrafine and mass splittings among $3P$ multiplet in our unquenched quark model (UQM) studies. The mass difference of $��_{b2}$ and $��_{b1}$ in $3P$ multiplet measured by CMS collaboration ($10.6 \pm 0.64 \pm 0.17$ MeV) is very close to our theoretical prediction ($12$ MeV). Our corresponding mass splitting of $��_{b1}$ and $��_{b0}$ enables us to predict more precisely the mass of $��_{b0}(3P)$ to be ($10490\pm 3$) MeV. Moreover, we predict ratios of the radiative decays of $��_{bJ}(nP)$ candidates, both in UQM and quark potential model. Our predicted relative branching fraction of $��_{b0}(3P)\to��(3S)��$ is one order of magnitude smaller than $��_{b2}(3P)$, this naturally explains the non-observation of $��_{b0}(3P)$ in recent CMS search. We hope these results might provide useful references for forthcoming experimental searches.

We propose a new model to create a light meson in the heavy quarkonium transition, which is inspired by the Nambu$-$Jona-Lasinio (NJL) model. Hadronic transitions of $J^{PC}=1^{--}$ higher charmonia with the emission of an $��$ meson are studied in the framework of the proposed model. The model shows its potential to reproduce the observed decay widths and make predictions for the unobserved channels. We present our predictions for the decay width of $��\to J/����$ and $��\to h_{c}(1P)��$, where $��$ are higher $S$ and $D$ wave vector charmonia, which provide useful references to search for higher charmonia and determine their properties in forthcoming experiments. The predicted branching fraction $\mathcal B(��(4415)\to h_{c}(1P)��)=4.62\times 10^{-4}$ is one order of magnitude smaller than the $J/����$ channel. Estimates of partial decay width $��(Y \to J/����)$ are given for $Y(4360)$, $Y(4390)$ and $Y(4660)$ by assuming them as $c\bar{c}$ bound states with quantum numbers $3 ^3D_1$, $3 ^3D_1$ and $5 ^3S_1$, respectively. Our results are in favor of these assignments for $Y(4360)$ and $Y(4660)$. The corresponding experimental data for these $Y$ states has large statistical errors which do not provide any constraint on the mixing angle if we introduce $S-D$ mixing. To identify $Y(4390)$, precise measurements on its hadronic branching fraction are required which are eagerly awaited from BESIII., version published in Phys. Rev. D

We study the dipion transitions $��(4S) \rightarrow ��(nS) ��^+��^-$ $(n=1,2)$. In particular, we consider the effects of the two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$ as well as bottom meson loops. The strong pion-pion final-state interactions, especially including channel coupling to $K\bar{K}$ in the $S$-wave, are taken into account model-independently by using dispersion theory. Based on a nonrelativistic effective field theory we find that the contribution from the bottom meson loops is comparable to those from the chiral contact terms and the $Z_b$-exchange terms. For the $��(4S) \rightarrow ��(2S) ��^+��^-$ decay, the result shows that including the effects of the $Z_b$-exchange and the bottom meson loops can naturally reproduce the two-hump behavior of the $����$ mass spectra. Future angular distribution data are decisive for the identification of different production mechanisms. For the $��(4S) \rightarrow ��(1S) ��^+��^-$ decay, we show that there is a narrow dip around 1 GeV in the $����$ invariant mass distribution, caused by the final-state interactions. The distribution is clearly different from that in similar transitions from lower $��$ states, and needs to be verified by future data with high statistics. Also we predict the decay width and the dikaon mass distribution of the $��(4S) \rightarrow ��(1S) K^+ K^-$ process., 25 pages, 8 figures, predictions of the decay width and the dikaon mass distribution of the $\Upsilon(4S) \rightarrow \Upsilon(1S) K^+ K^-$ process added, more discussions added

Within the framework of dispersion theory, we analyze the dipion transitions between the lightest $��$ states, $��(nS) \rightarrow ��(mS) ����$ with $m < n \leq 3$. In particular, we consider the possible effects of two intermediate bottomoniumlike exotic states $Z_b(10610)$ and $Z_b(10650)$. The $����$ rescattering effects are taken into account in a model-independent way using dispersion theory. We confirm that matching the dispersive representation to the leading chiral amplitude alone cannot reproduce the peculiar two-peak $����$ mass spectrum of the decay $��(3S) \rightarrow ��(1S) ����$. The existence of the bottomoniumlike $Z_b$ states can naturally explain this anomaly. We also point out the necessity of a proper extraction of the coupling strengths for the $Z_b$ states to $��(nS)��$, which is only possible if a Flatt��-like parametrization is used in the data analysis for the $Z_b$ states., 21 pages, 6 figures. The final version published in Phys. Rev. D 93, 034030 (2016)

The $p p \to n K^+ ��^+(1385)$ reaction is a very good isospin $3/2$ filter for studying $��^{++*}$ resonance decaying to $K^+��^+(1385)$. Within the effective Lagrangian method, we investigate the $��(1385)$ (spin-parity $J^P = 3/2^+$) hadronic production in the $��^+ p \to K^+ ��^+(1385)$ and $p p \to n K^+ ��^+(1385)$ reactions. For $��^+ p \to K^+ ��^+(1385)$ reaction, in addition to the "background" contributions from $t$-channel $K^{*0}$ exchange, $u$-channel $��(1115)$ and $��^0(1193)$ exchange, we also consider the contribution from the $s$-channel $��^*(1940)$ resonance, which has significant coupling to $K��(1385)$ channel. We show that the inclusion of the $��^*(1940)$ resonance leads to a fairly good description of the low energy experimental total cross section data of $��^+ p \to K^+ ��^+(1385)$ reaction. Basing on the study of $��^+ p \to K^+��^+(1385)$ reaction and with the assumption that the excitation of $��^*(1940)$ resonance dominant the $pp \to n K^+ ��^+(1385)$ reaction, we calculate the total and differential cross sections of $p p \to n K^+ ��^+(1385)$ reaction. It is shown that the new experimental data support the important role played by the $��^*(1940)$ resonance with a mass in the region of $1940$ MeV and a width of around $200$ MeV. We also demonstrate that the invariant mass distribution and the Dalitz Plot provide direct information of the $��^+(1385)$ production, which can be tested by future experiments., Published in Phys. Rev. C. arXiv admin note: substantial text overlap with arXiv:1302.0468

Within the framework of the effective Lagrangian approach, we perform a thorough analysis of the $J/��\to P��(��^*)$, $J/��\to VP$, $V\to P��(��^*)$, $P\to V��(��^*)$ and $P\to����(��^*)$ processes, where $V$ stand for light vector resonances, $P$ stand for light pseudoscalar mesons, and $��^*$ subsequently decays into lepton pairs. The processes with light pseudoscalar mesons $��$ and $��'$ are paid special attention to and the two-mixing-angle scheme is employed to describe their mixing. The four mixing parameters both in singlet-octet and quark-flavor bases are updated in this work. We confirm that the $J/��\to ��(��^{\prime})��^{(*)}$ processes are predominantly dominated by the $J/��\to ��_c ��^{*} \to ��(��^{\prime})��^{(*)}$ mechanism. Predictions for the $J/��\to P ��^+��^-$ are presented. A detailed discussion on the interplay between electromagnetic and strong transitions in the $J/��\to VP$ decays is given., 29 pages, 8 figures and 6 tables. References added. Accepted by Phys.Rev.D

The $��p \to ��p ��^0$ reaction near threshold is studied within an effective Lagrangian method. The production process is described by single-pion and single-kaon exchange. In addition to the role played by the $��^*(1385)$ resonance of spin-parity $J^P = 3/2^+$, the effects of a newly proposed $��^*$ ($J^P = 1/2^-$) state with mass and width around $1380$ MeV and $120$ MeV are investigated. We show that our model leads to a good description of the experimental data on the total cross section of the $��p \to ��p ��^0$ reaction by including the contributions from the possible $��^*(\frac{1}{2}^-)$ state. However, the theoretical calculations by considering only the $��^*(1385)$ resonance fail to reproduce the experimental data, especially for the enhancement close to the reaction threshold. On the other hand, it is found that the single-pion exchange is dominant. Furthermore, we also demonstrate that the angular distributions provide direct information of this reaction, hence could be useful for the investigation of the existence of the $��^*(\frac{1}{2}^-)$ state and may be tested by future experiments., 8 pages, 5 figures

By using an effective Lagrangian method, we study the effects of a newly proposed $��^*(1/2^-)$ state with mass around 1380 MeV in the initial-state polarized $��N\rightarrow K^{+} ��^*(1385) \rightarrow K^{+} ����$ process near threshold. The theoretical predictions for the helicity cross sections $��_{3/2}$, $��_{1/2}$ as well as their ratios, and the angular distributions of $��$ in the $����$ center-of-mass system are given. It is found that assuming $��^*(1/2^-)$ exists or not, these physical quantities are distinctly different. So our results could be useful for the investigation of the existence of $��^*(1/2^-)$ when the experimental data are available in the future., version published in PRC, 16 pages, 5 figures, more comments added

In the present work, we apply the one-boson-exchange potential (OBEP) model to investigate the possibility of Y(2175) and $��(2225)$ as bound states of $��\bar��(^3S_1)$ and $��\bar��(^1S_0)$ respectively. We consider the effective potential from the pseudoscalar $��$-exchange and $��^{'}$-exchange, the scalar $��$-exchange, and the vector $��$-exchange and $��$-exchange. The $��$ and $��^{'}$ meson exchange potential is repulsive force for the state $^1S_0$ and attractive for $^3S_1$. The results depend very sensitively on the cutoff parameter of the $��$-exchange ($��_��$) and least sensitively on that of the $��$-exchange ($��_��$). Our result suggests the possible interpretation of Y(2175) and $��(2225)$ as the bound states of $��\bar��(^3S_1)$ and $��\bar��(^1S_0)$ respectively.

In this work we make a systematic analysis of the correlated processes $J/��\to ����(1440)/f_1(1420)$ with $��(1440)/f_1(1420)\to K\bar{K}��$, $������$ and $3��$, where the role played by the so-called "triangle singularity mechanism" (TSM) is clarified. Our results agree well with the experimental data and suggest a small fraction of $f_1(1420)$ contributions in these processes. This study confirms our conclusion in [Phys. Rev. Lett. 108, 081803 (2012)] that the dynamic feature of the TSM can be recognized by the strong narrow peak observed in the $����$ invariant mass spectrum of $��(1440)\to 3��$ with anomalously large isospin violations. Nevertheless, we explicitly demonstrate that the TSM can produce obvious peak position shifts for the same $��(1440)$ or $f_1(1420)$ state in different decay channels. This is a strong evidence that the $��(1405)$ and $��(1475)$ are actually the same state, i.e. $��(1440)$. We also make an analysis of the radiative decays of $��(1440)\to ��V$ ($V=��$, $��^0$ or $��$) which shows that such a one-state prescription seems not to have a conflict with the so-far existing experimental data. Our analysis may shed a light on the long-standing puzzling question on the nature of $��(1405)$ and $��(1475)$., Revtex, 17 pages and 7 eps figures; revised version to appear in PRD

The resonances ($\eta_c,\chi_{c0,c2}$) contribution to two-photon exchange (TPE) effects in $e^+ e^- \leftrightarrow p \bar{p}$ is calculated in a simple hadronic model. The calculation shows the TPE contributions by resonance $\chi_{c2}$, which are dependent on the unknown phases $\phi_{E,M}$ of proton's time-like form factors $G_{E,M}$, are much larger than the TPE contributions by non-resonance and are comparable with measurement precision of coming PANDA detector at $\sqrt{s} \sim M_{\chi_{c2}}$ for most $\phi_{E,M}$., Comment: 8 pages, 6 figures; a global factor in the calculation is corrected

The BES-III Collaboration recently report the observation of anomalously large isospin violations in $J/��\to ����(1405/1475) \to ����^0 f_0(980)\to ��+3��$, where the $f_0(980)$ in the $����$ invariant mass spectrum appears to be much narrower ($\sim$ 10 MeV) than the peak width ($\sim$50 MeV) measured in other processes. We show that a mechanism, named as triangle singularity (TS), can produce a narrow enhancement between the charged and neutral $K\bar{K}$ thresholds, i.e., $2m_{K^\pm}\sim 2m_{K^0}$. It can also lead to different invariant mass spectra for $��(1405/1475)\to a_0(980)��$ and $K\bar{K}^*+c.c.$, which can possibly explain the long-standing puzzle about the need for two close states $��(1405)$ and $��(1475)$ in $������$ and $K\bar{K}��$, respectively. The TS could be a key to our understanding of the nature of $��(1405/1475)$ and advance our knowledge about the mixing between $a_0(980)$ and $f_0(980)$., 4 pages and 7 eps figures; Journal-matched version

The abundant $��'$ events have been collected at the Beijing Electron Positron Collider-II (BEPCII) that could undoubtedly provide us with a great opportunity to study the more attractive charmonium decays. As has been noticed before, in the process of $J/��$ decaying to the baryonic final states, $p K^- \bar��$, the evident $��^*$ and $N^*$ bands have been observed. Similarly, by using the product of $��_{cJ}$ from $��'$ radiative decay, we may confirm it or find some extra new resonances. $��_{c0}$'s data samples will be more than $��_{c1,2}$ taking into account the larger branching ratio of $��'\to����_{c0}$. Here, we provide explicit partial wave analysis formulae for the very interesting channel $��'\to����_{c0}\to ��p K^- \bar��$., 7 pages, 1 figure, version in Chin.Phys.C

The value of the $N^*(1535)N��$ coupling constant $g_{N^*N��}$ derived from the $N^*(1535) \to N��\to N ����$ decay is compared with that deduced from the radiative decay $N^*(1535) \to N ��$ using the vector-meson-dominance model. On the basis of an effective Lagrangian approach, we show that the value of $g_{N^*N��}$ extracted from the available experimental data on the two decays are consistent, though the error bars are rather large., 4 pages, 4 figures. To appear in Phys. Rev. C

In the framework chiral SU(3) quark model, the baryon spectra within the band of $N\leq 2$ are studied, and the effect of the confining potential in different configurations, namely the $\Delta$-mode and Y-mode are compared. In the same way, the baryon spectra in the extended chiral SU(3) quark model, in which additional vector meson exchanges are introduced, are also calculated. It is shown that a reasonable baryon spectrum in the chiral SU(3) quark model can be achieved no matter whether the $\Delta$-mode or the Y-mode confining potential is employed. In the extended chiral SU(3) quark model, several energy levels are further improved. The resultant binding energies of excited baryon states in different confining modes deviate just by a few to several tens MeV, and it is hard to justify which confining mode is the dominant one. The non-strange baryon strong decay widths are further discussed in the point-like meson emission model by using the wave-function obtained in the spectrum calculation. The resultant widths can generally explain the experimental data but still cannot distinguish which confining mode is more important in this simple decay mode., Comment: 22 pages, 12 figures

In this work, we study the isospin-violating decay of $��\to ����^0$ and quantify the electromagnetic (EM) transitions and intermediate meson exchanges as two major sources of the decay mechanisms. In the EM decays, the present datum status allows a good constraint on the EM decay form factor in the vector meson dominance (VMD) model, and it turns out that the EM transition can only account for about $1/4\sim 1/3$ of the branching ratio for $��\to ����^0$. The intermediate meson exchanges, $K\bar{K}(K^*)$ (intermediate $K\bar{K}$ interaction via $K^*$ exchanges), $K\bar{K^*}(K)$ (intermediate $K\bar{K^*}$ rescattering via kaon exchanges), and $K\bar{K^*}(K^*)$ (intermediate $K\bar{K^*}$ rescattering via $K^*$ exchanges), which evade the naive Okubo-Zweig-Iizuka (OZI) rule, serve as another important contribution to the isospin violations. They are evaluated with effective Lagrangians where explicit constraints from experiment can be applied. Combining these three contributions, we obtain results in good agreement with the experimental data. This approach is also extended to $J/��(��^\prime)\to ����^0$, where we find contributions from the $K\bar{K}(K^*)$, $K\bar{K^*}(K)$ and $K\bar{K^*}(K^*)$ loops are negligibly small, and the isospin violation is likely to be dominated by the EM transition., Revised version resubmitted to PRD; Additional loop contributions included; Conclusion unchanged

The low-energy S-wave pi N and K N scatterings are studied by the K-matrix approach within the meson exchange framework. The t-channel meson exchanges, especially rho and sigma exchanges, are found to play a very important role in these two processes. The t-channel rho exchange determines the isospin structure of the scattering amplitudes, it gives attractive force in the low isospin state but repulsive force in the high isospin state. The t-channel sigma exchange gives a very large contribution in these two processes, while it is negligible in meson-meson S-wave scatterings., Comment: 11 pages, 3 figures

We investigate the possibility of producing the enhancement observed in $J/��\to ��X$ with $X\to ����$ at BES by intermediate meson rescatterings through $f_0(1710)\to PP\to ����$, $f_0(1710)\to VV\to ����$, and $f_0(1710)\to SS\to ����$. We find that intermediate meson rescatterings can produce some enhancement near the $����$ threshold. Implications about the property of this enhancement are discussed., 12 pages, 6 figures; Version to appear in Phys. Rev. D

$K��$ $S$ wave scattering is studied using a chiral unitary approach (ChUT) taking into account coupled channels. With the amplitudes derived from the lowest order chiral Lagrangian as the kernel of a set of coupled channel Bathe-Salpeter equations, the $I=1/2$ $S$ wave $K��$ scattering phase shifts below 1.2 GeV can be fitted by one parameter, a subtraction constant, and a scalar resonance corresponding to the controversial $��$ ($K^*_0(800)$) can be generated dynamically. A good description of the $I=3/2$ $S$ wave $K��$ scattering phase shifts below 1.2 GeV can also be obtained. An artificial singularity in the conventional cut-off method of the 2-meson loop integral of the ChUT is found. The formalism is applied to deal with the $S$ wave $K��$ final state interaction (FSI) in the decay $J/��\to {\bar K}^{*0}(892)K^+��^-$, and a qualitatively good fit to the data is achieved. The role of $��$ in the decay is discussed., 23 pages, 6 figures; comparison with the results from the Roy equation analysis added. Version accepted for publication in Nucl. Phys. A

With accumulation of high statistics data at BES and CLEO-c, many new interesting channels can get enough statistics for partial wave analysis (PWA). Among them, $��\to ��p\bar p, ����\bar ��, ����\bar��, ����\bar ��$ channels provide a good place for studying baryon-antibaryon interactions; the double radiative decays $��\to����V$ with $V\equiv ��,��,��$ have a potential to provide information on the flavor content of any meson resonances (R) with positive charge parity ($C=+$) and mass above 1 GeV through $��\to��R \to����V$; $��(2S)\to����_{c0,1,2}$ with $��_{c0,1,2}\to K\bar K ��^+��^- $ and $2��^+2��^-$ decays are good processes to study $��_{cJ}$ charmonium decays. Using the covariant tensor formalism, here we provide theoretical PWA formulae for these channels., 20 pages

The double radiative decays $��\to����V$ with $V\equiv ��,��,��$ have a potential to provide information on the flavor content of any meson resonances (R) with positive charge parity ($C=+$) and mass above 1 GeV through $��\to��R \to����V$. To get the information, one needs both high statistic data and partial wave analysis (PWA). While high statistic data will be available soon at CLEO-c and BES-III, here we provide theoretical PWA formulae for these $��$ double radiative decay channels in the covariant tensor formalism., 9 pages, added references

We generalize our previous work on \pi\pi scattering to K\pi scattering, and re-analyze the experiment data of K\pi scattering below 1.6 GeV. Without any free parameter, we explain K\pi I=3/2 S-wave phase shift very well by using t-channel rho and u-channel K^* meson exchange. With the t-channel and u-channel meson exchange fixed as the background term, we fit the K\pi I=1/2 S-wave data of the LASS experiment quite well by introducing one or two s-channel resonances. It is found that there is only one s-channel resonance between K\pi threshold and 1.6 GeV, i.e., K_0^*(1430) with a mass around 1438~1486 MeV and a width about 346 MeV, while the t-channel rho exchange gives a pole at (450-480i) MeV for the amplitude., Comment: REVTeX4 file, 11 pages and 3 figures

The experimental isoscalar $\pi\pi\to\pi\pi$ S-wave amplitude squared below 1.75 GeV is characterized by a very broad structure $f_0(400-1200)$ with two narrow dips due to its destructive interference with the $f_0(980)$ and $f_0(1500)$. The $f_0(1370)$ and $f_0(1710)$ do not show up clearly in the $\pi\pi\to\pi\pi$ S-wave amplitude due to their weak coupling to $\pi\pi$. This paper is about the controversial nature of the broad $f_0(400-1200)$. We decompose it into two parts, i.e., t-channel $\rho$ meson exchange plus an additional s-channel resonance $f_0(X)$. With the t-channel $\rho$ meson exchange fixed by the isotensor $\pi\pi\to\pi\pi$ S-wave scattering, we re-fit the CERN-Munich (CM) data on $\pi\pi$ scattering to get parameters for the $f_0(X)$. We find that the $f_0(X)$ is very broad with a nearby pole at (1.67-0.26i) GeV, while the t-channel $\rho$ meson exchange part produces a pole at (0.36-0.53i) GeV. The implication of our results for the study of $\sigma$ and glueball is discussed., Comment: 11 pages, 3 figures

We carefully analyze the relative branching ratios of $4��$ final states $��^+��^-��^+��^-$, $��^+��^-��^0��^0$ and $��^0��^0��^0��^0$, from various resonances of $J^{PC}=0^{++}$, $0^{-+}$, $2^{++}$. We find that the Bose symmetry interference effects would make their ratios to obviously differ from the naive counting values without considering these effects. The results should be applied to estimate correctly various $4��$ decay branching ratios of relevant resonances.

We study the final-state interactions in $B \to ��K$ decays through $B \to VV \to ��K$ processes where the inelastic rescattering occurs via single pion exchange. The next-to-leading order low energy effective Hamiltonian and BSW model are used to evaluate the weak transition matrix elements and the final-state interactions. We found that the final-state interaction effects in $B \to ��K^* \to ��K$ processes are significant. The Fleischer-Mannel relation about the CKM angle $��$ may be significantly modified., Latex, 14 pages, with 1 figures and 2 tables

Lattice QCD and other theoretical models predict that the 0(-+), 2(++) and 2(-+) glueballs have masses in the range of 2.0 to 2.4 GeV. For resonances in such an energy range, three-body decay modes are expected to be large. The strategy for looking for these glueballs and the newest results from studying Crystal Barrel data on the three-body annihilation of proton-antiproton in flight are presented., Comment: Latex with espcrc1.sty, 10 pages, 7 figures. Invited talk at the International Conference on Low Energy Antinucleon Physics (LEAP98), Sardinia, Italy, September 1998

We propose to create a secondary beam of neutral kaons in Hall D at Jefferson Lab to be used with the GlueX experimental setup for strange hadron spectroscopy. The superior CEBAF electron beam will enable a flux on the order of $1\times 10^4~K_L/sec$, which exceeds the flux of that previously attained at SLAC by three orders of magnitude. The use of a deuteron target will provide first measurements ever with neutral kaons on neutrons. The experiment will measure both differential cross sections and self-analyzed polarizations of the produced $\Lambda$, $\Sigma$, $\Xi$, and $\Omega$ hyperons using the GlueX detector at the Jefferson Lab Hall D. The measurements will span CM $\cos\theta$ from $-0.95$ to 0.95 in the range W = 1490 MeV to 2500 MeV. The new data will significantly constrain the partial wave analyses and reduce model-dependent uncertainties in the extraction of the properties and pole positions of the strange hyperon resonances, and establish the orbitally excited multiplets in the spectra of the $\Xi$ and $\Omega$ hyperons. Comparison with the corresponding multiplets in the spectra of the charm and bottom hyperons will provide insight into he accuracy of QCD-based calculations over a large range of masses. The proposed facility will have a defining impact in the strange meson sector through measurements of the final state $K\pi$ system up to 2 GeV invariant mass. This will allow the determination of pole positions and widths of all relevant $K^\ast(K\pi)$ $S$-,$P$-,$D$-,$F$-, and $G$-wave resonances, settle the question of the existence or nonexistence of scalar meson $\kappa/K_0^\ast(700)$ and improve the constrains on their pole parameters. Subsequently improving our knowledge of the low-lying scalar nonet in general., Comment: Final version of the KLF Proposal [C12-19-001] approved by JLab PAC48. The intermediate version of the proposal was posted in arXiv:1707.05284 [hep-ex]. 103 pages, 52 figures, 8 tables, 324 references. Several typos were fixed

In recent years there has been a rapidly growing body of experimental evidence for existence of exotic, multiquark hadrons, i.e. mesons which contain additional quarks, beyond the usual quark-antiquark pair and baryons which consist of more than three quarks. In all cases with robust evidence they contain at least one heavy quark Q=c or b, the majority including two heavy quarks. Two key theoretical questions have been triggered by these discoveries: (a) how are quarks organized inside these multiquark states -- as compact objects with all quarks within one confinement volume, interacting via color forces, perhaps with an important role played by diquarks, or as deuteron-like hadronic molecules, bound by light-meson exchange? (b) what other multiquark states should we expect? The two questions are tightly intertwined. Each of the interpretations provides a natural explanation of parts of the data, but neither explains all of the data. It is quite possible that both kinds of structures appear in Nature. It may also be the case that certain states are superpositions of the compact and molecular configurations. This Whitepaper brings together contributions from many leading practitioners in the field, representing a wide spectrum of theoretical interpretations. We discuss the importance of future experimental and phenomenological work, which will lead to better understandingof multiquark phenomena in QCD., 47 pages, 10 figures. Corresponding authors: Marek Karliner, Elena Santopinto