Search

We adopt the quark pair creation model to investigate the light meson emissions of several charmonium-like states. The quark pair creation model is applied to the four-body systems, and we calculate the pion/kaon emissions of the $X(4700)$, $Z_c(4430)$, $Y(4230)$, $Y(4360)$, $Y(4390)$ and $Y(4660)$ within the compact tetraquark assumptions. It is found that the pion/kaon decay widths for the $X(4700)$ and $Z_c(4430)$ are relatively small, while the partial decay widths for the resonances $Y(4230)$, $Y(4360)$, $Y(4390)$ and $Y(4660)$ are significant. We expect that our exploration of these decay behaviors can provide useful information for future experimental searches and theoretical interpretations., 10 pages, 4 figures, to be published in Chinese Physics C

Inspired by the recent observation of a new structure, $X(4014)$, in the process $\gamma\gamma\to \gamma\psi(2S)$, we evaluate the possibility of assigning $X(4014)$ as a $D^\ast \bar{D}^\ast$ molecular state with $I(J^{PC})=0(0^{++})$ by investigating the hidden charm decays of $X(4014)$. The partial widths of $J/\psi\omega$, $ \eta_{c}\eta$ and $\eta_{c}\eta^{\prime}$ channels are evaluated to be about $(0.41\sim 5.00)$, $(2.05\sim7.49)$ and $(0.11\sim0.51)\ \mathrm{MeV}$, respectively. Considering the experimental observation and the present estimations, we proposed to search $X(4014)$ in the $\gamma \gamma \to J/\psi \omega$ process in Belle II., Comment: 7 pages, 5 figures, accepted for publication in Phys. Rev. D

In this work, we systematically investigate the mass spectra of fully-heavy hexaquarks within a constituent quark model by including the color Coulomb potential, linear confining potential, and spin-spin interactions. Our results show that all of the fully-heavy hexaquarks lie above the corresponding baryon-baryon thresholds, and thus no stable compact one exists. These states may subsist as resonances and decay into two fully-heavy baryons easily through the fall-apart mechanism, which can be searched in future experiments., Comment: 8 pages, 2 figures, comments and suggestions are welcome

Recent lattice QCD calculations showed that a $d_{N��}$ dibaryon state similar to the deuteron with small binding energy may exist. In this work we propose a hadronic molecular approach to study the dynamical properties of this exotic state. We use a phenomenological Lagrangian approach to describe the coupling of the $d_{N��}$ state to its constituents and the decays into conventional hadrons, $d_{N��} \to ����$ and $d_{N��} \to ����$. Predictions for the sum of the decay rates are in the range of a few hundred keV. In addition, we find that the $d_{N��} \to ����$ mode is dominant, preferably searched for in a future RHIC experiment.

In this work, we investigated the decays of the fully open-flavor tetraquark state $X_0(2900)$ which was observed by the LHCb Collaboration very recently. Here, the $X_0(2900)$ was assigned as a $S-$wave $\bar D^\ast K^\ast$ hadronic molecule with $I=0$, and the effective lagrangian approach was applied to estimate the partial decay widths. Moreover, we also predicted the decay behaviors of the other unobserved $X_{J(J=1,2)}$, which were the spin partners of the $X_0(2900)$ in the $S-$wave $\bar D^\ast K^\ast$ picture. It was pointed out that the $X_1$ state with $I=0$ was a broad state with the width more than one hundred MeV, while another $X_2$ state with $I=0$ was a narrow state with the width approaching half of that for the $X_0(2900)$. In addition, our results also showed that the $\bar D^\ast K$ mode was expected to be the dominant decay mode for both $X_1$ and $X_2$. Searching for those unobserved $X_{J(J=1,2)}$ in the future experiments might be helpful to understand the nature of $X_0(2900)$.

The $��$ meson gravitational form factors are studied based on a light-front constituent quark model which has been successfully employed to calculate its generalized parton distributions and some low-energy observables. The distributions of energy, spin, pressures, and shear forces inside the $��$ meson are explicitly given.

In the present work, we assign the newly observed $P_c(4312)$ as a $I(J^P)= \frac{1}{2} (\frac{1}{2})^-$ molecular state composed of $\Sigma_c \bar{D}$, while $P_c(4440)$ and $P_c(4457)$ as $\Sigma_c \bar{D}^\ast$ molecular states with $I(J^P)= \frac{1}{2} (\frac{1}{2})^-$ and $\frac{1}{2} (\frac{3}{2})^-$, respectively. In this molecular scenario, we investigate the $P_c\to J/\psi p$ process of these three states and further predict the ratios of the $\mathcal B(P_c\to J/\psi p)$ and those of $\mathcal B(\Lambda_b\to P_c K)$ between these three states, which could serve as a crucial test of the present molecular scenario., Comment: 6 pages, 5 figures

We investigate the mass spectrum of the $ss \bar s \bar s$ tetraquark states within the relativized quark model. By solving the Schr\"{o}dinger-like equation with the relativized potential, the masses of the $S-$ and $P-$wave $ss \bar s \bar s$ tetraquarks are obtained. The screening effects are also taken into account. It is found that the observed resonant structure $X(2239)$ in the $e^+e^- \to K^+K^-$ process by BESIII Collaboration can be assigned as a $P-$wave $1^{--}$ $ss \bar s \bar s$ tetraquark state. Furthermore, the radiative transition and strong decay behaviors of this structure are also estimated, which can provide helpful information for future experimental searches., Comment: 7 pages, 2 figures. Add the strong decay behaviors. Version accepted by Chinese Physics C

Recently, the BESIII Collaboration reported a new measurement of the $��_c ��$ decay mode of $Z_c^{(\prime)}$, which motivated us to study the inner structure of $Z_c^{(\prime)}$ via investigating the hidden charm decays of these two $Z_c$ states. We consider the {triangle loop mechanism} contribution in the hidden charm decays of $Z_c^{(\prime)}$. Our estimations indicate that the triangle loop mechanism plays an important role in the decays of the $Z_c^{(\prime)}$, where our results are in agreement with the experimental observations in a reasonable parameter range. Furthermore, we point out that the $Z_c^{(\prime)}$ can be interpreted as the hadronic molecules, while the tetraquark scenario is less favored.

$d^\ast(2380)$ was observed by WASA-at-COSY collaborations in the nuclear reaction recently. Its particularly narrow width may indicate the new QCD-allowed hadronic structure. To further confirm the existence of this peculiar particle in a totally different kind of reaction, we study the opportunity for searching $\bar{d}^\ast$ in the $��(nS)$ (with n=1, 2, 3) decay. As a phenomenological study, our framework is based on SU(3) chiral quark model. By virtue of the unitarity of $S$-matrix and crossing symmetry, we study the imaginary part of the forward scattering amplitudes between $��(nS)$ and $d^\ast$. The scattering process is mainly governed by the quark-meson interaction. We examine both the pseudoscalar and vector meson contribution in the intermediate state. Hopefully, our results show that it's quite possible to find $\bar{d}^\ast$ in this decay mode in the future., 7 pages, 3 figures, 1 table

In this paper, the $��$ meson impact parameter dependent parton distributions and the impact parameter dependent form factors are introduced and discussed. By employing a Gaussian form wave packet, we calculate the impact parameter distributions of $��$ meson based on a light-front constituent quark model.

The $��$ meson polarized generalized parton distribution functions, its structure functions $g_1$ and $g_2$ and its axial form factors ${\tilde G}_{1,2}$ are studied based on a light-front quark model for the first time. Comparing our obtained moments of $g_1$ to lattice QCD calculation, we find that our results are reasonably consistent to the Lattice predictions.

There are polarized structure functions $b_{1-4}$ for the spin-1 deuteron. We calculated the leading-twist tensor structure function $b_1$ by using convolution description for the deuteron. We found large differences between our theoretical functions and HERMES experimental data on $b_1$. Although higher-twist effects should be considered in obtaining experimental $b_1$, it suggests a possible existence of new hadron physics mechanism for spin-1 hadrons. Furthermore, we found that there are significant distributions at large Bjorken $x$. In future, an experimental measurement is planned at JLab for $b_1$ and there is a possibility of a proton-deuteron Drell-Yan experiment at Fermilab with the tensor-polarized deuteron, so that further theoretical studies are needed for clarifying the physics origin of tensor structure in terms of quark and gluon degrees of freedom., 4 pages, 2 eps figures, 22nd International Spin Symposium (Spin-2016), University of Illinois, Champaign, Illinois, USA, September 25-30, 2016

The structure of $d^*(2380)$ is re-studied with the single cluster structure in the chiral SU(3) quark model which has successfully been employed to explain the $N-N$ scattering data and the binding energy of deuteron. The binding behavior of such a six quark system is solved by using a variational method. The trial wave function is chosen to be a combination of a basic spherical symmetric component of $[(0s)^6]_{orb}$ in the orbital space with $0\hbar\omega$ excitation and an inner structural deformation component of $[(0s)^5(1s)]_{orb}$ and $[(0s)^4(0p)^2]_{orb}$ in the orbital space with $2\hbar\omega$ excitation, both of which are in the spatial [6] symmetry. It is shown that the mass of the system is about $2356$ MeV, which is qualitative consistent with the result both from the two-cluster configuration calculation and from the data measured by the WASA Collaborations. This result tells us that as long as the medium-range interaction due to the chiral symmetry consideration is properly introduced, the mass of system will be reduced in a rather large extent. It also implies that the observed $d^*$ is a six-quark bound state with respect to the $\Delta\Delta$ threshold, which again supports the conclusion that $d^*$ is a hexaquark dominant state., Comment: 6 pages, 3 figures.

We study $��$ meson unpolarized generalized parton distributions based on a light-front constituent quark model where the quark-antiquark-meson vertex is constructed under the symmetric loop momentum convention. The form factors and some other low-energy observables of the $��$ meson are calculated. Moreover, the contributions to the form factors and generalized parton distributions from the valence and nonvalence regimes are discussed and analyzed in detail. In the forward limit, the usual structure functions are estimated as well. In addition, by evolving the moments of the obtained structure functions to the scale of the lattice calculation, we give the factorization scale of our quark model. It is found that the present phenomenological model is reasonable to describe the general properties of $��$ meson.

We study the near-threshold incoherent $��$ photoproduction on the deuteron based on a model of $��N \to ��N$, consisting of Pomeron, $(��, ��)$ exchanges, and a $J^P = 3/2^-$ resonance, which describes the low energy $��p \to ��p$ LEPS data well, including the peak in the forward differential cross section. The calculation is done up to double rescatterings, with the spin dependence of the elementary $��N \to ��N$ amplitude retained throughout the calculation. The Fermi motion and final-state interactions (FSI) are all properly treated as prescribed by realistic nucleon-nucleon interaction. The couplings of the resonance to $��n$ and $��n$ channels are estimated with the help of a constituent quark model. The main features of the LEPS and CLAS data are described reasonably well except for some quantitative discrepancies at very low energies and low momentum transfers regions. It is found that contributions of Fermi motion, $pn$ FSI, and resonance are all indispensable in bridging the differences between the single-scattering results and the data. The off-shell rescattering is found to be important as it cancels out a large portion of the on-shell contribution. The discrepancies at low momentum transfer region might be related to the binning size of the data. No peak is found to be associated with the weak resonance as it gets smeared out by the Fermi motion and FSI with deuterium target. The problem at very low energy region hints at the possible contributions from other mechanisms and should be investigated in depth with the use of recent high statistics $��p \to ��p$ data from CLAS.

We investigate the masses of $cs \bar c \bar s$ tetraquark states in a diquark-antidiquark picture employing the relativized quark model proposed by Godfrey and Isgur. Only the antitriplet diquark states in color space are calculated. The diquark masses are obtained with the relativized potential firstly, and then the diquark and antidiquark are treated as the usual antiquark and quark, respectively, and the masses of the tetraquark states are obtained by solving the Schr\"{o}dinger equation with the relativized potential between the diquark and antidiquark. The theoretical uncertainties induced by screening effects are also taken into account. It is found that the resonance of $X(4140)$ can be regarded as the $cs \bar c \bar s$ tetraquark ground states, and the $X(4700)$ can be assigned as the $2S$ excited tetraquark state. When the internal excited diquarks are taken into account, the resonance of $X(4500)$ can be explained as the tetraquark composed of one $2S$ scalar diquark and one scalar antidiquark. In our approach, the $X(4274)$ cannot be explained as a tetraquark state, however, it can be a good candidate of the conventional $\chi_{c1}(3^3P_1)$ state. In addition, other charmonium-like states $\chi_{c0}(3915)$, $X(4350)$, $X(4630)$ and $X(4660)$, as the $cs \bar c \bar s$ tetraquark states, are also discussed., Comment: Minor changes, 8 pages, 2 figures

The electromagnetic form factors and low-energy observables of deuteron are studied with the help of the light-front approach, where the deuteron is regarded as a weekly bound state of a proton and a neutron. Both the $S-$ and $D-$wave interacting vertexes among deuteron, proton, and neutron are taken into account. Moreover, the regularization functions are also introduced. In our calculations, the vertex and the regularization functions are employed to simulate the momentum distribution inside the deuteron. Our numerical results show that the light-front approach can roughly reproduce the deuteron electromagnetic form factors, like charge $G_0$, magnetic $G_1$, and quadrupole $G_2$, in the low $Q^2$ region. The important role of the $D-$wave vertex on $G_2$ is also addressed.

We study the strong decay channels $P_c^+(4380) \to J/��p$ and $P_c^+(4450) \to J/��p$ under $��_c \bar{D}^*$ molecular state ansatz. With various spin-parity assignments, the partial decay widths of $J/��p$ final state are calculated. Our results show that all the $P$ wave $��_c {\bar D}^*$ assignments are excluded, while $S$ wave $��_c {\bar D}^*$ pictures for $P_c(4380)$ and $P_c(4450)$ are both allowed by present experimental data. The $J^P=3/2^-$ $��_c^* \bar{D}$ and $��_c^* \bar{D}^*$ molecules are also discussed in the heavy quark limit, and find that the $��_c^* \bar{D}$ system for $P_c(4380)$ is possible. More experimental information on spin-parities and partial decay widths and theoretical investigations on other decay modes are needed to clarify the nature of the two $P_c$ states., 7 pages, 6 figures, 2 tables. More discussions are added. Version accepted by Phys. Rev. D

We study the radiative decays of the $Z_c(3900)^0$ in a hadronic molecule picture, where the $Z_c(3900)$ is treated as a $D \bar{D}^\ast +c.c$ hadronic molecule. The partial widths of $\Gamma(Z_c(3900)^0 \to \gamma \eta_c(2S))$ and $\Gamma(Z_c(3900)^0 \to \gamma \chi_{c0})$ are predicted to be of order 10 keV and the cross sections for $\sigma(e^+ e^- \to \pi^0 Z_c(3900) \to \pi^0 \gamma \eta_c(2S))$ and $\sigma(e^+ e^- \to \pi^0 Z_c(3900) \to \pi^0 \gamma \chi_{c0})$ are of order 0.1 pb at 4.23 GeV, which may be accessible for the BESIII and forthcoming BelleII., Comment: 8 pages, 11 figures, Phys.Rev.D version

We report on a theoretical study of the $��^- p \to D^- D^0 p$ reaction near threshold within an effective Lagrangian approach. The production process is described by $t$ channel $D^{*0}$ meson exchange, $s$-channel nucleon pole, and $u$ channel $��^{++}_{c}$ exchange. In our work, the final $D^0 p$ results from the ground $��^+_c(2286)$ state and also dominantly from the excited $��^+_c(2940)$ state which is assumed as a $D^{*0} p$ molecular state with spin parity $J^P = \frac{1}{2}^+$ or $\frac{1}{2}^-$. We calculate the total cross section of the $��^- p \to D^- D^0 p$ reaction. It is shown that the spin parity assignment of $\frac{1}{2}^-$ for $��^+_c(2940)$ gives a sizable enhancement for the total cross section in comparison with a choice of $J^p = \frac{1}{2}^+$. However, our theoretical result of the total cross section is sensitive to the value of the cutoff parameter involved in the form factor of the exchanged off-shell particles. Moreover, we also calculate the second order differential cross section and find it can be used to determine the parity of the $��^+_c(2940)$. It is expected that our model calculations can be tested by future experiments at J-PARC in Japan., Published version. Phys. Rev. D 92, 034029 (2015)

We investigate the neutral hidden charm pentaquark states $P_c^0(4380)$ and $P_c^0(4450)$ in $��^-p \to J/��n$ reaction within an effective Lagrangian approach. The background contributions for the process mainly come from $t$-channel $��$ and $��$ meson exchanges. The contributions of $P_c^0(4380)$ and $P_c^0(4450)$ states give clear peak structures in the magnitude of 1 $��$b at center of mass energy 4.38 GeV and 4.45 GeV in the total cross sections. Hence, this reaction may provide a new good platform to search for neutral $P_c$ states. It is expected that our estimated total cross sections together with the angular distributions can be tested by future experiments at J-PARC., 9 pages, 6 figures. minor changes to text and added references

The discrepancy between the PQCD calculation and the CLEO data for $��_{c1}\to ��V$ ($V=��^0,\,��,\,��$) stimulates our interest in exploring extra mechanism of $��_{c1}$ decay. In this work, we apply an important non-perturbative QCD effect, i.e., hadronic loop mechanism, to study $��_{c1}\to ��V$ radiative decay. Our numerical result shows that the theoretical results including the hadronic loop contribution and the PQCD calculation of $��_{c1}\to ��V$ are consistent with the corresponding CLEO data of $��_{c1}\to ��V$. We expect further experimental measurement of $��_{c1}\to ��V$ at BES-III, which will be helpful to test the hadronic loop effect on $��_{c1}$ decay., 7 pages, 2 figures. Accepted for publication in Eur. Phys. J. C

The role of Poincar\'e covariant space-time translations is investigated in the case of a relativistic quantum mechanics approach to the pion charge form factor. It is shown that the related constraints are generally inconsistent with the assumption of a single-particle current, which is most often referred to. The only exception is the front-form approach with $q^+=0$. How accounting for the related constraints, as well as restoring the equivalence of different RQM approaches in estimating form factors, is discussed. Some extensions of this work and, in particular, the relationship with a dispersion-relation approach, are presented. Conclusions relative to the underlying dynamics are given., Comment: 6 pages, 2 figures, proceedings of the QNP2009 international conference (Beijing, oct. 2009), to be published in Chinese Physics C

Constraints related to transformations of currents under space-time translations have been considered for the relativistic quantum mechanics calculation of form factors of J=0 systems composed of scalar constituents with equal masses. Accounting for these constraints amounts to take into account many-body currents that restore the equality of the momentum transferred separately to the system and to the constituents, which holds in field-theory approaches but is not generally fulfilled in relativistic quantum mechanics ones. When this was done, discrepancies between results from different approaches could be found to vanish. The results are extended here to systems composed of spin-1/2 constituents with unequal masses. Moreover, as far as the equivalence of different approaches is concerned, some intermediate step could be skipped and the presentation of these results therefore slightly differs from the previous one. Due to the technical aspect of present results, this work is not aimed to be published but it could be useful for some applications like the form factors of the pion or kaon particles., 30 pages

Two-photon annihilate contributions in the process $e^+ + e^- \to p + \bar{p}$ including $N$ and $��$ intermediate are discussed in a simple hadronic model. The corrections to the unpolarized cross section and polarized observables $P_x,P_z$ are presented. The results show the two-photon annihilate correction to unpolarized cross section is small and its angle dependence becomes weak at small $s$ after considering the $N$ and $��(1232)$ contributions simultaneously, while the correction to $P_z$ is enhanced., 5 pages

The electromagnetic form factors, charge radii and decay constants of pion, K and K*(892) are calculated using the three forms of relativistic kinematics: instant form, point form and (light) front form. Simple representations of the mass operator together with single quark currents are employed with all the forms. Making use of previously fixed parameters, together with the constituent quark mass for the strange quark, a reasonable reproduction of the available data for form factors, charge radii and decay constants of pion, rho, K and K*(892) is obtained in front form. With instant form a similar description, but with a systematic underestimation of the vector meson decay constants is obtained using two different sets of parameters, one for pion and rho and another one for K and K*(892). Point form produces a poor description of the data., Accepted in Eur. Phys. Jour. A (2005)

We derive the exchange currents of pseudoscalar, vector, and scalar mesons from Feynman diagrams, and use them to calculate the magnetic form factors of nucleon and $��(1232)$. The magnetic moments and electromagnetic radii are obtained by using those form factors and the parameters determined from the masses of nucleon and $��(1232)$. We find the magnetic moments and electromagnetic radii of nucleon and $��(1232)$ can be produced very well in the extended Goldstone-boson-exchange model (GBE) in which all of pseudoscalar, vector and scalar meson nonet are included. The magnetic moments of $��(1232)$ are closer to experiment values and results from lattice calculation than the results obtained by the model without other mesons except for pion and sigma., 15 pages,5 figures

The structure of $d^*(2380)$ is re-studied with the single cluster structure in the chiral SU(3) quark model which has successfully been employed to explain the scattering and binding behaviors of baryonic systems. The mass and width are explicitly calculated with two types of trial wave functions. The result shows that the $(0s)^6 [6]_{orb}$ configuration is easy to convert to the configuration with the same $[6]_{orb}$ symmetry but $2\hbar \omega$ excitation back and forth, however, it is seldom to turn into a two-cluster configuration with a (1s) relative motion in between. The resultant mass and width are about $2394$MeV and $25$MeV, respectively, and the stable size is about $0.75fm$, which are consistent with both the results in the two-cluster configuration calculation and the data measured by the COSY collaboration. It seems that the observed $d^*$ is a six-quark dominated exotic state with a spherical shape and breath mode in the coordinate space. Moreover, if $d^*$ does have $2\hbar \omega$ excitation, the $d^* \to np\pi\pi\pi$ decay mode might be a good place to distinguish the real structure of the observed phenomenon by COSY. The masses of various isospin-spin states of six-light-quark systems are also computed. It is shown that by considering the coupling with the configurations with $2\hbar \omega$ excitations, only the mirror state with $IS$=$30$ will be lower down to the place where whose mass is slightly higher than the value of the $\Delta\Delta$ threshold., Comment: This paper has been withdrawn by the author as the further investigation is needed