arXiv subjects
Publications and source records attributed to Yu-Bing Dong.
The $ρ$ 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.
$d^\ast(2380)$ 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 $Υ(nS)$ (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 $Υ(nS)$ 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.
In this paper, the $ρ$ 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 $ρ$ meson based on a light-front constituent quark model.
Spin-1 hadrons have additional structure functions not present for spin 1/2 hadrons. These could probe novel aspects of hadron structure and QCD dynamics. For the deuteron, the tensor structure function $b_1$ inherently mixes quark and nuclear degrees of freedom. These proceedings discuss two standard convolution models applied to calculations of the deuteron $b_1$ structure functions. We find large differences with the existing HERMES data and other convolution model calculations. This leaves room for non-standard contributions to $b_1$ in the deuteron. We also discuss the influence of higher twist nuclear effects in the model calculations and data extraction at kinematics covered in HERMES and Jefferson Lab.
We study $ρ$ 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 $ρ$ 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 $ρ$ meson.
Tensor-polarized structure functions of a spin-1 hadron are additional observables which do not exist for the spin-1/2 nucleon. They could probe novel aspects of the internal hadron structure. Twist-2 tensor-polarized structure functions are $b_1$ and $b_2$, and they are related by the Callan-Gross-like relation in the Bjorken scaling limit. In this work, we theoretically calculate $b_1$ in the standard convolution description for the deuteron. Two different theoretical models, a basic convolution description and a virtual nucleon approximation, are used for calculating $b_1$ and their results are compared with the HERMES measurement. We found large differences between our theoretical results and the data. Although there is still room to improve by considering higher-twist effects and in the experimental extraction of $b_1$ from the spin asymmetry $A_{zz}$, there is a possibility that the large differences require physics beyond the standard deuteron model for their interpretation. Future $b_1$ studies could shed light on a new field of hadron physics. In particular, detailed experimental studies of $b_1$ will start soon at the Thomas Jefferson National Accelerator Facility. In addition, there are possibilities to investigate tensor-polarized parton distribution functions and $b_1$ at Fermi National Accelerator Laboratory and a future electron-ion collider. Therefore, further theoretical studies are needed for understanding the tensor structure of the spin-1 deuteron, including a new mechanism to explain the large differences between the current data and our theoretical results.
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.
We study the masses of open charm and bottom tetraquark states within the diquark-antidiquark scenario in the relativized quark model proposed by Godfrey and Isgur. The diquark and antidiquark masses are firstly solved by relativized quark potential, and then treated as the usual antiquark and quark, respectively. The masses of tetraquark states are obtained by solving the Schrödinger-type equation between the new diquark and antidiquark. We find the masses of $sq\bar b\bar q$ tetraquark configuration are much higher than that of $X(5568)$. This conclusion disfavors the possibility of $X(5568)$ as a tetraquark state within the diquark-antidiquark scenario. Further experimental searches are needed to clarify the nature of the signal observed by D0 collaboration.
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 Schrödinger 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 $χ_{c1}(3^3P_1)$ state. In addition, other charmonium-like states $χ_{c0}(3915)$, $X(4350)$, $X(4630)$ and $X(4660)$, as the $cs \bar c \bar s$ tetraquark states, are also discussed.
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 $2\hbar ω$ 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 $2\hbar ω$ excitation, the $d^* \to npπππ$ 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 $2\hbar ω$ 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 $ΔΔ$ threshold.
We study the strong decay channels $P_c^+(4380) \to J/ψp$ and $P_c^+(4450) \to J/ψp$ under $Σ_c \bar{D}^*$ molecular state ansatz. With various spin-parity assignments, the partial decay widths of $J/ψp$ final state are calculated. Our results show that all the $P$ wave $Σ_c {\bar D}^*$ assignments are excluded, while $S$ wave $Σ_c {\bar D}^*$ pictures for $P_c(4380)$ and $P_c(4450)$ are both allowed by present experimental data. The $J^P=3/2^-$ $Σ_c^* \bar{D}$ and $Σ_c^* \bar{D}^*$ molecules are also discussed in the heavy quark limit, and find that the $Σ_c^* \bar{D}$ 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.
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 $Γ(Z_c(3900)^0 \to γη_c(2S))$ and $Γ(Z_c(3900)^0 \to γχ_{c0})$ are predicted to be of order 10 keV and the cross sections for $σ(e^+ e^- \to π^0 Z_c(3900) \to π^0 γη_c(2S))$ and $σ(e^+ e^- \to π^0 Z_c(3900) \to π^0 γχ_{c0})$ are of order 0.1 pb at 4.23 GeV, which may be accessible for the BESIII and forthcoming BelleII.
We investigate the neutral hidden charm pentaquark states $P_c^0(4380)$ and $P_c^0(4450)$ in $π^-p \to J/ψn$ reaction within an effective Lagrangian approach. The background contributions for the process mainly come from $t$-channel $π$ and $ρ$ meson exchanges. The contributions of $P_c^0(4380)$ and $P_c^0(4450)$ states give clear peak structures in the magnitude of 1 $μ$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.
We report on a theoretical study of the $π^- p \to D^- D^0 p$ 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 $Σ^{++}_{c}$ exchange. In our work, the final $D^0 p$ results from the ground $Λ^+_c(2286)$ state and also dominantly from the excited $Λ^+_c(2940)$ 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 $π^- p \to D^- D^0 p$ reaction. It is shown that the spin parity assignment of $\frac{1}{2}^-$ for $Λ^+_c(2940)$ 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 $Λ^+_c(2940)$. It is expected that our model calculations can be tested by future experiments at J-PARC in Japan.
The analytical forms of the interaction potentials between one S-wave and one P-wave heavy mesons as well as the potentials between two P-wave heavy mesons are deduced based on a chiral quark model. Our results explicitly show the attractive property between two heavy mesons. Consequently, a series of possible molecular states are obtained. It is expected that our study might shed some light on the popular discussions of the newly observed XYZ states.
The role of Poincaré covariant space-time translations is investigated in the case of the pseudoscalar-meson charge form factors calculated within a relativistic quantum mechanics framework. It is shown that this role extends beyond the standard energy-momentum conservation, which is accounted for in all works based on this general approach. It implies constraints that have been largely ignored until now but should be nevertheless fulfilled to ensure the full Poincaré covariance. The violation of these constraints, which is more or less important depending on the form of relativistic quantum mechanics that is employed, points to the validity of using a single-particle current, which is generally assumed in calculations of form factors. In short, these constraints concern the relation of the momentum transferred to the constituents to the one transferred to the system, which most often differ in relativistic quantum mechanics while they are equal in field theory. How to account for the constraints, as well as restoring the equivalence of different relativistic quantum mechanics approaches in estimating form factors, is discussed. It is mentioned that the result so obtained can be identified to a dispersion-relation one. A short conclusion relative to the underlying dynamics is given in the pion case.
An effective potential in a meson-meson system is discussed based on the SU(3) chiral constituent quark model, and the analytic form of the potential is explicitly given. In addition, the effective potential is employed to study the bound state problem of $ωϕ$, which is related to the new resonance of $f_0(1810)$ observed in BESII very recently.
The discrepancy between the PQCD calculation and the CLEO data for $χ_{c1}\to γV$ ($V=ρ^0,\,ω,\,ϕ$) stimulates our interest in exploring extra mechanism of $χ_{c1}$ decay. In this work, we apply an important non-perturbative QCD effect, i.e., hadronic loop mechanism, to study $χ_{c1}\to γV$ radiative decay. Our numerical result shows that the theoretical results including the hadronic loop contribution and the PQCD calculation of $χ_{c1}\to γV$ are consistent with the corresponding CLEO data of $χ_{c1}\to γV$. We expect further experimental measurement of $χ_{c1}\to γV$ at BES-III, which will be helpful to test the hadronic loop effect on $χ_{c1}$ decay.