Search

Very recently, the LHCb Collaboration reported the doubly charmed tetraquark state $T_{cc}^+$ below the $D^{*+}D^0$ threshold about $273$ keV. As a very near-threshold state, its long-distance structure is very important. In the molecular scheme, we relate the coupling constants of $T_{cc}^+$ with $D^{*0}D^+$ and $D^{*+}D^0$ to its binding energy and mixing angle of two components with a coupled-channel effective field theory. With the coupling constants, we investigate the kinetically allowed strong decays $T_{cc}^+\to D^0D^0\pi^+$, $T_{cc}^+\to D^+D^0\pi^0$ and radiative decays $D^+D^0 \gamma$. Our results show that the decay width of $T_{cc}^+\to D^0D^0\pi^+$ is the largest one, which is just the experimental observation channel. Our theoretical total strong and radiative widths are in favor of the $T_{cc}^+$ as a $|D^{*+}D^0\rangle$ dominated bound state. The total strong and radiative width in the single channel limit and isospin singlet limit are given as $59.7^{+4.6}_{-4.4} \text{ keV}$ and $46.7^{+2.7}_{-2.9} \text{ keV}$, respectively. Our calculation is cutoff-independent and without prior isospin assignment. The absolute partial widths and ratios of the different decay channels can be used to test the structure of $T_{cc}^+$ state when the updated experimental results are available., Comment: 7 pages, 4 figures; Accepted version by Letter in Physical Review D

We systematically calculate the mass spectrum of the higher excited fully-charmed tetraquark $cc\bar c\bar c$ states including the S-wave radial excitations and the P-wave states with a nonrelativistic quark model. The quark model is composed of a vector one-gluon-exchange (OGE) and a scalar linear confinement interaction with the parameters determined by the charmonium spectrum. In the calculation, we consider both the $3_c-\bar 3_c$ and the $6_c-\bar{6}_c$ color representations. For the $cc\bar c\bar c $ state, the $6_c-\bar 6_c$ component is located lower than the $\bar 3_c-3_c$ one because of the stronger attractive interactions between the diquark and antidiquark. We focus on two excited modes and their properties for the P-wave tetraquarks. The mass splitting for the $\rho$-mode excitations with different color configurations is large. The low-lying $6_c-\bar 6_c$ $\rho$-mode component helps to explain the small mass gap between the ground S-wave and the P-wave tetraquark states. The recently observed $X(6900)$ state may be the candidate of the first radially excited tetraquarks with $J^{PC}=0^{++}$ or $2^{++}$, or the $1^{+-}$ or $2^{-+}$ P-wave states based on the mass spectrum. Moreover, the lowest $T_c$ states with the exotic $J^{PC}$ quantum numbers $0^{--}$ and $1^{-+}$ may decay into the P-wave $\eta_c J/\psi$ and di-$J/\psi$ modes, respectively. The future experimental search of these $T_c$ states will enrich the hadronic spectrum., Comment: 15 pages, 3 figures. Version published in PRD

Recently, the hidden charm tetraquark states $Z_{cs}(3985)$ and $Z_{cs}(4000)$ with strangeness were observed by the BESIII and LHCb collaborations, respectively, which are great breakthroughs for exploring exotic QCD structures. The first and foremost question is whether they are the same state. In this work, we explore the implications of the narrower state $Z_{cs}(3985)$ in BESIII and the wider one $Z_{cs}(4000)$ in LHCb as two different states. Within a solvable nonrelativistic effective field theory, we include the possible violations of heavy quark spin symmetry and SU(3) flavor symmetry in a comprehensive approach. If $Z_{cs}(3985)$ and $Z_{cs}(4000)$ are two different states, our results show that $Z_{cs}(4000)/Z_{cs}(3985)$ is the pure $(|\bar{D}_s^*D\rangle+/- |\bar{D}_sD^*\rangle)/\sqrt{2}$ state, and the SU(3) flavor partner of $Z_{c}(3900)$ is $Z_{cs}(4000)$ rather than the $Z_{cs}(3985)$. Another two important consequences are the existence of a tensor $\bar{D}_s^*D^*$ resonance with mass about 4126 MeV and width 13 MeV, and the suppression of the decay mode $Z_{cs}(3985) \to J/\psi K$. The two consequences can be tested in experiments and distinguish the two-state interpretation from the one-state scheme., Comment: 8 pages,3 figures and 1 table; Accepted version by Science Bulletin

In this work, we investigate the SU(3) flavor symmetry, heavy quark spin symmetry and their breaking effects in the di-meson systems. We prove the existence of the $[\bar{D}_{s}^{*}D_{s}^{*}]^{0^{++}}$, $[\bar{D}_{s}^{*}D_{s}/\bar{D}_{s}^{}D_{s}^*]^{1^{+-}}$, and $[\bar{D}_{s}^{*}D_{s}^{*}]^{1^{+-}}$ bound states as the consequence of two prerequisites in the SU(3) flavor symmetry and heavy quark spin symmetry. The first prerequisite, the $X(3872)$ as the weakly $\bar{D}^{*}D/\bar{D} D^{*}$ bound state is supported by its mass and decay branching ratios. The second prerequisite, the existence of the $[\bar{D}_{s}D_{s}]^{0^{++}}$ bound state is supported by the lattice QCD calculation [arXiv:2011.02542(hep-lat)] and the observation of $\chi_{c0}(3930)$ by the LHCb Collaboration[Phys.Rev.Lett.125,242001, Phys.Rev.D102,112003]. We hope the future experimental analyses can search for these bound states in the $B\to D_{(s)}^{(*)}\bar{D}^{(*)}_{(s)}h$ processes ($h$ denotes the light hadrons). The $[\bar{D}_{s}^{*}D_{s}^{*}]^{0^{++}}$ bound state is also expected to be reconstructed in the $J/\psi \phi$ final state in the $B\to J/\psi \phi K$ decay., Comment: 9 pages, 5 figures; add the coupled-channel discussions in EFT; to be published in Science Bulletin

We study the newly observed charmoniumlike state $Z_{cs}(3985)$ in the framework of chiral effective field theory. The interaction kernel of the $\bar{D}_sD^\ast/\bar{D}^\ast_sD$ system is calculated up to the next-to-leading order with the explicit chiral dynamics. With the fitted parameters extracted from the $Z_c(3900)$ data as inputs, the mass, width and event distributions of the $Z_{cs}(3985)$ are very consistent with the experimental measurements. Our studies strongly support the $Z_{cs}(3985)$ as the partner of the $Z_c(3900)$ in the SU(3)$_f$ symmetry and the $\bar{D}_sD^\ast/\bar{D}^\ast_sD$ molecular resonance with the same dynamical origin as the other charged heavy quarkoniumlike states. We precisely predict the resonance parameters of the unobserved states in $\bar{D}_s^\ast D^\ast$, $B^\ast_s \bar{B}/B_s\bar{B}^\ast$ and $B_s^\ast\bar{B}^\ast$ systems, and establish a complete spectrum of the charged charmoniumlike and bottomoniumlike states with the $I(J^P)$ quantum numbers $1(1^+)$ and $\frac{1}{2}(1^+)$, respectively., Comment: 5 pages, 3 figures and 1 table

Recently, for the first time, the BESIII Collaboration reported the strange hidden charm tetraquark states $Z_{cs}(3985)^-$ in the $K^+$ recoil-mass spectrum near the $D_{s}^{-}D^{*0}/ D_{s}^{*-}D^{0}$ mass thresholds in the processes of $e^{+}e^{-}\to K^{+}(D_{s}^{-}D^{*0}+D_{s}^{*-}D^{0})$ at $\sqrt{s}=4.681$ GeV. The significance was estimated to be 5.3 $\sigma$. We show that the newly observed $Z_{cs}(3985)^-$ state is the $U$-spin partner of $Z_c(3900)^{-}$ as a resonance within coupled-channel calculation in the $\text{SU(3)}_F$ symmetry and heavy quark spin symmetry (HQSS). In the $\text{SU(3)}_F$ symmetry, we introduce the $G_{U/V}$ parity to construct the flavor wave functions of the $Z_{cs}$ states. In a unified framework, we consider the $J/\psi\pi(K)$, $\bar{D}_{(s)}{D}^*/\bar{D}_{(s)}^*{D}$ coupled-channel effect with the contact interaction. With the masses and widths of $Z_c(3900)$ and $Z_c(4020)$, we determine all the unknown coupling constants. We obtain mass and width of $Z_{cs}(3985)$ in good agreement with the experimental results, which strongly supports the $Z_{cs}$ states as the $U/V$-spin partner states of the charged $Z_c(3900)$. We also calculate the ratio of the partial decay widths of $Z_{cs}(3985)$, which implies that the $\bar{D}_sD^*/\bar{D}^*_s D$ decay modes are dominant. We also predict the $Z_{cs}^\prime$ states with a mass around $4130$ MeV and width around $30$ MeV, which are the $U/V$-spin partner states of the charged $Z_c(4020)$ and HQSS partner states of the $Z_{cs}(3985)$. In the hidden bottom sector, we predict the strange tetraquark states $Z_{bs}$ and $Z_{bs}^\prime$ with a mass around 10700 MeV and 10750 MeV, which are the $U/V$-spin partner states of $Z_{b}(10610)^{\pm}$ and $Z_b(10650)^{\pm}$, respectively., Comment: 6 pages, 2 figures

We systematically study the mass spectrum and strong decays of the S-wave $\bar c\bar s q q$ states in the compact tetraquark scenario with the quark model. The key ingredients of the model are the Coulomb, the linear confinement, and the hyperfine interactions. The hyperfine potential leads to the mixing between different color configurations, as well as the large mass splitting between the two ground states with $I(J^P)=0(0^+)$ and $I(J^P)=1(0^+)$. We calculate their strong decay amplitudes into the $\bar D^{(*)}K^{(*)}$ channels with the wave functions from the mass spectrum calculation and the quark interchange method. We examine the interpretation of the recently observed $X_0(2900)$ as a tetraquark state. The mass and decay width of the $I(J^P)=1(0^+)$ state are $M=2941$ MeV and $\Gamma_X=26.6$ MeV, respectively, which indicates that it might be a good candidate for the $X_0(2900)$. Meanwhile, we also obtain an isospin partner state $I(J^P)=0(0^+)$ with $M=2649$ MeV and $\Gamma_{X\rightarrow \bar D K}=48.1$ MeV, respectively. Future experimental search for $X(2649)$ will be very helpful., Comment: 11 pages, 4 figures

We generalize the framework of chiral effective field theory to study the interactions of the isovector $D^\ast\bar{D}^{(\ast)}$ and $B^\ast\bar{B}^{(\ast)}$ systems up to the next-to-leading order, in which the long-, mid-, and short-range force contributions as well as the $S$-$D$ wave mixing are incorporated. Based on the Lippmann-Schwinger equation, we fit the invariant mass distributions of the elastic channels measured by the BESIII and Belle Collaborations. Our results indicate that the four charged charmoniumlike and bottomoniumlike states $Z_c(3900)$, $Z_c(4020)$ and $Z_b(10610)$, $Z_b(10650)$ can be well identified as the $D\bar{D}^{\ast},D^\ast\bar{D}^{\ast}$ and $B\bar{B}^{\ast},B^\ast\bar{B}^{\ast}$ molecular resonances. The bound state explanations are vetoed in our framework. Our study favors the $Z_c$ and $Z_b$ states are the twin partners under the heavy quark symmetry., Comment: 6 pages, 3 figures and 1 table

We study the $DN$ and $D^\ast N$ interactions to probe the inner structure of $\Sigma_c(2800)$ and $\Lambda_c(2940)$ with the chiral effective field theory to the next-to-leading order. We consider the contact term, one-pion-exchange and two-pion-exchange contributions to characterize the short-, long- and mid-range interactions of the $D^{(\ast)}N$ systems. The low energy constants of the $D^{(\ast)}N$ systems are related to those of the $N\bar{N}$ interaction with quark level Lagrangian that inspired by the resonance saturation model. The $\Delta(1232)$ degree of freedom is also included in the loop diagrams. The attractive potential in the $[DN]_{J=1/2}^{I=1}$ channel is too weak to form bound state, which indicates the explanation of $\Sigma_c(2800)$ as the compact charmed baryon is more reasonable. Meanwhile, the potentials of the isoscalar channels are deep enough to yield the molecular states. We obtain the masses of the $[DN]_{J=1/2}^{I=0}$, $[D^\ast N]_{J=1/2}^{I=0}$ and $[D^\ast N]_{J=3/2}^{I=0}$ systems to be $2792.0$ MeV, $2943.6$ MeV and $2938.4$ MeV, respectively. The $\Lambda_c(2940)$ is probably the isoscalar $D^\ast N$ molecule considering its low mass puzzle. Besides, the $\Lambda_c(2940)$ signal might contain the spin-$\frac{1}{2}$ and spin-$\frac{3}{2}$ two structures, which can qualitatively explain the significant decay ratio to $D^0p$ and $\Sigma_c\pi$. We also study the $\bar{B}^{(\ast)}N$ systems and predict the possible molecular states in the isoscalar channels. We hope experimentalists could hunt for the open charmed molecular pentaquarks in the $\Lambda_c^+\pi^+\pi^-$ final state., Comment: 11 pages, 4 figures and 4 tables

We calculate the effective potentials of the $\Xi_c\bar{D}^{(\ast)}$, $\Xi_c^\prime\bar{D}^{(\ast)}$ and $\Xi_c^\ast\bar{D}^{(\ast)}$ systems with the chiral effective field theory up to the next-to-leading order. We simultaneously consider the short-, intermediate- and long-range interactions. With the newly observed $P_c$ spectra as inputs, we construct the quark-level contact Lagrangians to relate the low energy constants to those of $\Sigma_c\bar{D}^{(\ast)}$ with the help of quark model. Our calculation indicates there are seven bound states in the $I=0$ strange hidden charm $[\Xi_c^\prime\bar{D}^{(\ast)}]_J~(J=\frac{1}{2},\frac{3}{2})$ and $[\Xi_c^\ast\bar{D}^{(\ast)}]_J~(J=\frac{1}{2},\frac{3}{2},\frac{5}{2})$ systems. Our analyses also disfavor the $\Lambda_c\bar{D}^{(\ast)}$ bound states. However, we obtain three new hadronic molecules in the isoscalar $[\Xi_c\bar{D}^{(\ast)}]_J~(J=\frac{1}{2},\frac{3}{2})$ systems. The masses of $[\Xi_c\bar{D}]_{1/2}$, $[\Xi_c\bar{D}^{\ast}]_{1/2}$ and $[\Xi_c\bar{D}^{\ast}]_{3/2}$ are predicted to be $4319.4^{+2.8}_{-3.0}$ MeV, $4456.9^{+3.2}_{-3.3}$ MeV and $4463.0^{+2.8}_{-3.0}$ MeV, respectively. We also notice the one-eta-exchange influence is rather feeble. Binding solutions in the $I=1$ channels are nonexistent. We hope the future analyses at LHCb can seek for these new $P_{cs}$s in the $J\psi\Lambda$ final states, especially near the thresholds of $\Xi_c\bar{D}^{(\ast)}$., Comment: 9 pages, 2 figures, and 4 tables

We adopt the heavy baryon chiral perturbation theory to calculate the $\Sigma_cN$ interaction to the next-to-leading order. We consider the contact interactions, one-pion-exchange contributions, two-pion-exchange diagrams, and renormalization effects of the vertices, masses and wave functions. With the pion mass dependent expression, we fit the $\Sigma_cN$ interaction from HAL QCD calculation with $m_{\pi}\approx 410$ MeV and $m_{\pi}\approx 570$ MeV, and then extrapolate it to the physical pion mass. The $^3S_1(I=1/2)$ $\Sigma_{c}N$ interaction is weakly attractive but no bound solution is found. We also propose a quark model to estimate the leading order $\Sigma_cN$ contact interaction with the $NN$ interaction as input. This approach combining the quark model and the chiral effective field theory predicts a very attractive interaction in $^1S_0(I=3/2)$ $\Sigma_{c}N$ channel and a two-body bound state., Comment: 11 pages, 9 figures