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The explanation of some exotic states in the $csbar{c}bar{s}$ tetraquark system

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 Added by Hongxia Huang
 Publication date 2021
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and research's language is English




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Inspired by the recent observation of $chi_{c0}(3930)$, $X(4685)$ and $X(4630)$ by the LHCb Collaboration and some exotic resonances such as $X(4350)$, $X(4500)$, etc. by several experiment collaborations, the $csbar{c}bar{s}$ tetraquark systems with $IJ^{P}=00^+$, $01^+$ and $02^+$ are systematically investigated in the framework of the quark delocalization color screening model(QDCSM). Two structures, the meson-meson and diquark-antidiquark structures, as well as the channel-coupling of all channels of these two configurations are considered in this work. The numerical results indicate that the molecular bound state $bar{D}_{s}D_{s}$ with $IJ^{P}=00^+$ can be supposed to explain the $chi_{c0}(3930)$. Besides, by using the stabilization method, several resonant states are obtained. There are four $IJ^{P}=00^{+}$ states around the resonance mass 4035 MeV, 4385 MeV, 4524 MeV, and 4632 MeV, respectively; one $IJ^{P}=01^{+}$ state around the resonance mass 4327 MeV; and two $IJ^{P}=02^{+}$ states around the resonance mass 4419 MeV and 4526 MeV, respectively. All of them are compact tetraquarks. Among these states, $X(4350)$, $X(4500)$ and $X(4700)$ can be explained as the compact tetraquark state with $IJ^{P}=00^{+}$, and the $X(4274)$ is possible to be a candidate of the compact tetraquark state with $IJ^{P}=01^{+}$. More experimental tests are expected to check the existence of all these possible resonance states.



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In this work, we study systematically the mass splittings of the $qqbar{Q}bar{Q}$ ($q=u$, $d$, $s$ and $Q=c$, $b$) tetraquark states with the color-magnetic interaction by considering color mixing effects and estimate roughly their masses. We find that the color mixing effect is relatively important for the $J^P=0^+$ states and possible stable tetraquarks exist in the $nnbar{Q}bar{Q}$ ($n=u$, $d$) and $nsbar{Q}bar{Q}$ systems either with $J=0$ or with $J=1$. Possible decay patterns of the tetraquarks are briefly discussed.
The new members of the charm-strange family $D_{sJ}^{*}(2317)$, $D_{sJ}(2460)$ and $D_s(2632)$, which have the surprising properties, are challenging the present models. Many theoretical interpretations have been devoted to this issue. Most of authors suggest that they are not the conventional $cbar s$ quark model states, but possibly are four-quark states, molecule states or mixtures of a P-wave $cbar s$ and a four-quark state. In this work, we follow the four-quark-state picture, and study the masses of $cnbar nbar s/csbar sbar s$ states ($n$ is $u$ or $d$ quark) in the chiral SU(3) quark model. The numerical results show that the mass of the mixed four-quark state ($cnbar nbar s/csbar sbar s$) with spin parity $J^P=0^{+}$ might not be $D_s(2632)$. At the same time, we also conclude that $D_{sJ}^{*}(2317)$ and $D_{sJ}(2460)$ cannot be explained as the pure four-quark state.
206 - Kuang-Ta Chao , Shi-Lin Zhu 2020
We give a brief comment on the possible tetraquark states $cc bar c bar c$ observed by the LHCb experiment.
We have studied the masse spectra for the $ccbar{b}bar{b}$/$bbbar{c}bar{c}$ tetraquark states with quantum numbers $J^{P}=0^{pm},1^{pm}$, and $2^{+}$. We systematically construct the interpolating currents with various spin-parity quantum numbers and calculate their two-point correlation functions in the framework of QCD moment sum rule method. Our calculations show that the masses are about $12.3-12.4$ GeV for the positive parity $ccbar{b}bar{b}$ tetraquark ground states with $J^{P}=0^+, 1^+, 2^+$, while $12.8-13.1$ GeV for the negative parity channels with $J^{P}=0^-, 1^-$. The mass predictions for the positive parity $ccbar{b}bar{b}$ ground states are lower than the $B_{c}B_{c}$ threshold, implying that these tetraquarks can only decay via weak interaction and thus are expected to be stable and narrow.
The LHCb Collaboration has reported resonant activity in the channel $D^+ K^-$, identifying two components: $X_0(2900)$ with $J^P = 0^+$ at $2866 {pm} 7$ MeV, $Gamma_0=57{pm} 13$ MeV and $X_1(2900)$ with $J^P = 1^-$ at $2904 {pm} 7$ MeV, $Gamma_1=110{pm} 12$ MeV. We interpret the $X_0(2900)$ component as a $cs bar ubar d$ isosinglet compact tetraquark, calculating its mass to be $2863 {pm} 12$ MeV. This is the first exotic hadron with open heavy flavor. The analogous $bsbar ubar d$ tetraquark is predicted at $6213 {pm} 12$ MeV. We discuss possible interpretations of the heavier and wider $X_1(2900)$ state and examine potential implications for other systems with two heavy quarks.
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