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Register a new userThe doubly heavies: (Qbar Q qbar q), (Q Q qbar qbar) tetraquarks and (Q Q q) baryons
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Recent discoveries by Belle and BESIII of charged exotic quarkonium-like resonances provide fresh impetus for study of heavy exotic hadrons. In the limit N_c --> infinity, M_Q --> infinity, the (Qbar Q qbar q) tetraquarks (TQ-s) are expected to be narrow and slightly below or above the (Qbar q) and (Q qbar) two-meson threshold. The isoscalar TQ-s manifest themselves by decay to (Qbar Q) pi pi, and the ~30 MeV heavier charged isotriplet TQ-s by decays into (Qbar Q) pi. The new data strongly suggest that the real world with N_c=3, Q=c,b and q,q = u,d is qualitatively described by the above limit. We discuss the relevant theoretical estimates and suggest new signatures for TQ-s in light of the recent discoveries. We also consider baryon-like states (Q Q qbar qbar), which if found will be direct evidence not just for near-threshold binding of two heavy mesons, but for genuine tetraquarks with novel color networks. We stress the importance of experimental search for doubly-heavy baryons in this context.
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We have systematically calculated the mass spectra for S-wave and P-wave fully-charm $cbar{c}cbar{c}$ and fully-bottom $bbar{b}bbar{b}$ tetraquark states in the $mathbf{8}_{[Qbar{Q}]}otimes mathbf{8}_{[Qbar{Q}]}$ color configuration, by using the moment QCD sum rule method. The masses for the fully-charm $cbar ccbar c$ tetraquark states are predicted about $6.3-6.5$ GeV for S-wave channels and $7.0-7.2$ GeV for P-wave channels. These results suggest the possibility that there are some $mathbf{8}_{[cbar{c}]}otimes mathbf{8}_{[cbar{c}]}$ components in LHCbs di-$J/psi$ structures. For the fully-bottom $bbar{b}bbar{b}$ system, their masses are calculated around 18.2 GeV for S-wave tetraquark states while 18.4-18.6 GeV for P-wave ones, which are below the $eta_beta_b$ and $Upsilon(1S)Upsilon(1S)$ two-meson decay thresholds.
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.
We show how it is possible to define and compute the potential between $q$ and $bar q$ external sources in the singlet and octet (adjoint) representation of the colour group.
The compact tetraquark states with fully heavy quark contents $QQbar Qbar Q$ are studied as the bound states of the diquark-antidiquark within the Bethe-Salpeter framework. The (anti)diquark masses and form factors used are the same as we calculated the doubly heavy baryons in a previous work. Under the instantaneous approximation, the three-dimensional (Bethe-)Salpeter equation of the tetraquarks is derived and solved numerically to obtain the corresponding mass spectra and wave functions of the tetraquarks with $J^{PC}=0^{++}$, $1^{+-}$, and $2^{++}$. Our results show that the three ground states of $ccbar cbar c$ locate in the mass range of $6.4sim6.5$GeV, and the $bbbar bbar b$ states in mass range of $19.2sim19.3$GeV. The obtained relativistic wave functions naturally include the mixing effects from the possible $D$,(or $G$) partial waves, and then can be further used to do precise calculations of the tetraquark decays. Based on the obtained results, the LHCbs observation $X(6900)$ is less likely to be the ground states of compact $ccbar cbar c$ tetraquarks but might be the first or second excited states. In addition, a widely used propagator-like form factor is also investigated and discussed.
The mass spectra and decay properties of heavy quarkonia are computed in nonrelativistic quark-antiquark Cornell potential model. We have employed the numerical solution of Schrodinger equation to obtain their mass spectra using only four parameters namely quark mass ($m_c$, $m_b$) and confinement strength ($A_{cbar c}$, $A_{bbar b}$). The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are computed perturbatively to determine the mass spectra of excited $S$, $P$, $D$ and $F$ states. Digamma, digluon and dilepton decays of these mesons are computed using the model parameters and numerical wave functions. The predicted spectroscopy and decay properties for quarkonia are found to be consistent with available experimental observations and results from other theoretical models. We also compute mass spectra and life time of the $B_c$ meson without additional parameters. The computed electromagnetic transition widths of heavy quarkonia and $B_c$ mesons are in tune with available experimental data and other theoretical approaches.
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