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Register a new userThe triply heavy tetraquark states
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In the framework of an extended chromomagnetic model, we systematically study the mass spectrum of the $S$-wave $qQbar{Q}bar{Q}$ tetraquarks. Their mass spectra are mainly determined by the color interaction. For the $qcbar{c}bar{c}$, $qbbar{c}bar{c}$ and $qbbar{b}bar{b}$ tetraquarks, the color interaction favors the color-sextet $ket{(qQ)^{6_{c}}(bar{Q}bar{Q})^{bar{6}_{c}}}$ configuration over the color-triplet $ket{(qQ)^{bar{3}_{c}}(bar{Q}bar{Q})^{3_{c}}}$ one. But for the $qcbar{b}bar{b}$ tetraquarks, the color-triplet configuration is favored. We find no stable states which lie below the thresholds of two pseudoscalar mesons. The lowest axial-vector states with the $qQbar{b}bar{b}$ flavor configuration may be narrow. They lie just above the thresholds of two pseudoscalar mesons, but cannot decay into these channels because of the conservation of the angular momentum and parity.
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Within the framework of QCD sum rules, we have investigated the tetraquark states with three heavy quarks. We systematically construct the interpolating currents for the possible $ccbar{c}bar{q}$, $ccbar{b}bar{q}$, $bcbar{b}bar{q}$, $bbbar{b}bar{q}$ tetraquark states with quantum numbers $J^{P}=0^{+}$ and $J^{P}=1^{+}$. Using these interpolating currents, we have calculated the two-point correlation functions and extracted the mass spectra for the above tetraquark states. We also discuss the decay patterns of these tetraquarks, and notice that the $ccbar{c}bar{q}$, $ccbar{b}bar{q}$, $bcbar{b}bar{q}$ may decay quickly with a narrow width due to their mass spectra. The $bbbar{b}bar{q}$ tetraquarks are expected to be very narrow resonances since their OZI-allowed decay modes are kinematically forbidden. These states may be searched for in the final states with a $B$ meson plus a light meson or photon.
Spectrum of the doubly heavy tetraquarks, $bbbar qbar q$, is studied in a constituent quark model. Four-body problem is solved in a variational method where the real scaling technique is used to identify resonant states above the fall-apart decay thresholds. In addition to the two bound states that were reported in the previous study we have found several narrow resonant states above the $BB^*$ and $B^*B^*$ thresholds. Their structures are studied and are interpreted by the quark dynamics. A narrow resonance with spin-parity $J^P=1^+$ is found to be a mixed state of a compact tetraquark and a $B^*B^*$ scattering state. This is driven by a strong color Coulombic attraction between the $bb$ quarks. Negative-parity excited resonances with $J^P=0^-$, $1^-$ and $2^-$ form a triplet under the heavy-quark spin symmetry. It turns out that they share a similar structure to the $lambda$-mode of a singly heavy baryon as a result of the strongly attractive correlation for the doubly heavy diquark.
We calculate the masses of the $QQbar{q}bar{q}$ ($Q=c,b$; $q=u,d,s$) tetraquark states with the aid of heavy diquark-antiquark symmetry (HDAS) and the chromomagnetic interaction (CMI) model. The masses of the highest-spin ($J=2$) tetraquarks that have only the $(QQ)_{bar{3}_c}(bar{q}bar{q})_{3_c}$ color structure are related with those of conventional hadrons using HDAS. Thereafter, the masses of their partner states are determined with the mass splittings in the CMI model. Our numerical results reveal that: (i) the lightest $ccbar{n}bar{n}$ ($n=u,d$) is an $I(J^P)=0(1^+)$ state around 3929 MeV (53 MeV above the $DD^*$ threshold) and none of the double-charm tetraquarks are stable; (ii) the stable double-bottom tetraquarks are the lowest $0(1^+)$ $bbbar{n}bar{n}$ around 10488 MeV ($approx116$ MeV below the $BB^*$ threshold) and the lowest $1/2(1^+)$ $bbbar{n}bar{s}$ around 10671 MeV ($approx20$ MeV below the $BB_s^*/B_sB^*$ threshold); and (iii) the two lowest $bcbar{n}bar{n}$ tetraquarks, namely the lowest $0(0^+)$ around 7167 MeV and the lowest $0(1^+)$ around 7223 MeV, are near-threshold states. Moreover, we discuss the constraints on the masses of double-heavy hadrons. Specifically, for the lowest nonstrange tetraquarks, we obtain $T_{cc}<3965$ MeV, $T_{bb}<10627$ MeV, and $T_{bc}<7199$ MeV.
Open-heavy tetraquark states, especially those contain four different quarks have drawn much attention in both theoretical and experimental fields. In the framework of the improved chromomagnetic interaction (ICMI) model, we complete a systematic study on the mass spectra and possible strong decay channels of the $S$-wave open-heavy tetraquark states, $qqbar{q}bar{Q}$ ($q=u,d,s$ and $Q=c,b$), with different quantum number $J^P=0^+$, $1^+$, and $2^+$. The parameters in the ICMI model are extracted from the conventional hadron spectra and used directly to predict the mass of tetraquark states. Several compact bound states and narrow resonances are found in both charm-strange and bottom-strange tetraquark sectors, most of them as a product of the strong coupling between the different channels. Our results show the recently discovered four different flavors tetraquark candidates $X_0(2900)$ is probably compact $udbar{s}bar{c}$ state with quantum number $J^P=0^+$. The predictions about $X_0(2900)$ and its partners are expected to be better checked with other theories and future experiments.
In the framework of the color-magnetic interaction, we systematically investigate the mass spectrum of the tetraquark states composed of four heavy quarks with the $QQbar Qbar Q$ configuration in this work. We also show their strong decay patterns. Stable or narrow states in the $bbbar{b}bar{c}$ and $bcbar{b}bar{c}$ systems are found to be possible. We hope the studies shall be helpful to the experimental search for heavy-full exotic tetraquark states.
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