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Discovery potentials of double-charm tetraquarks

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 Added by Qin Qin
 Publication date 2020
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and research's language is English




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In this study, we investigate the discovery potential of double-charm tetraquarks $T^{{cc}}_{[bar{q}bar{q}]}$. We find that their production cross sections at the LHCb with $sqrt{s} = 13$ TeV reach $mathcal{O}(10^4)$ pb, which indicates that the LHCb has collected $mathcal{O}(10^8)$ such particles. Through the decay channels of $T^{{cc}}_{[bar{u}bar{d}]}to D^{+}K^{-}pi^{+}$ or $D^0D^+gamma$ (if stable) or $T^{{cc}}_{[bar{u}bar{d}]}to D^0D^{*+}to D^0D^0pi^+$ (if unstable), it is highly expected that they get discovered at the LHCb in the near future. We also discuss the productions and decays of the double-charm tetraquarks at future Tera-$Z$ factories.



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With the spin rearrangement, we have performed a comprehensive investigation of the decay patterns of the S-wave tetraquarks and P-wave tetraquarks where the P-wave excitation exists either between the diquark and anti-diquark pair or inside the diquark. Especially, we compare the decay patterns of $Y(4260)$ with different inner structures such as the conventional charmonium, the molecule, the P-wave tetraquark and the hybrid charmonium. We notice the $J/psi pipi$ mode is suppressed in the heavy quark symmetry limit if $Y(4260)$ is a molecular state. Moreover the hybrid charmonium and hidden-charm tetraquark have very similar decay patterns. Both of them decay into the $J/psi pipi$ and open charm modes easily. We also discuss the decay patterns of $X(3872)$, $Y(4360)$, and several charged states such as $Z_c(4020)$. The $h_cpi^{pm}$ decay mode disfavors the tetraquark assumption of $Z_c(4020)$.
We study strong decays of the possible fully-charm tetraquarks recently observed by LHCb, and calculate their relative branching ratios through the Fierz rearrangement. Together with our previous QCD sum rule study [Phys. Lett. B 773, 247 (2017)], our results suggest that the broad structure around $6.2$-$6.8$ GeV can be interpreted as an $S$-wave $ccbar c bar c$ tetraquark state with $J^{PC} = 0^{++}$ or $2^{++}$, and the narrow structure around 6.9 GeV can be interpreted as a $P$-wave one with $J^{PC} = 0^{-+}$ or $1^{-+}$. These structures were observed in the di-$J/psi$ invariant mass spectrum, and we propose to confirm them in the di-$eta_c$, $J/psi h_c$, $eta_c chi_{c0}$, and $eta_c chi_{c1}$ channels. We also propose to search for their partner states having the negative charge-conjugation parity in the $J/psi eta_c$, $J/psi chi_{c0}$, $J/psi chi_{c1}$, and $eta_c h_c$ channels.
The spectroscopic parameters and decay channels of the axial-vector tetraquark $T_{bb;overline{u}overline{s}}^{-}$ (in what follows, $T_{b: overline{s}}^{mathrm{AV}}$) are explored using the quantum chromodynamics (QCD) sum rule method. The mass and coupling of this state are calculated using two-point sum rules by taking into account various vacuum condensates, up to 10 dimensions. Our prediction for the mass of this state $m=(10215pm 250)~ mathrm{MeV}$ confirms that it is stable with respect to strong and electromagnetic decays and can dissociate to conventional mesons only via weak transformations. We investigate the dominant semileptonic $T_{b:overline{s} }^{mathrm{AV}} to mathcal{Z}_{b:overline{s}}^{0}loverline{ u}_l$ and nonleptonic $T_{b:overline{s}}^{mathrm{AV}} to mathcal{Z}_{b:overline{s} }^{0}M$ decays of $T_{b:overline{s}}^{mathrm{AV}}$. In these processes, $ mathcal{Z}_{b:overline{s}}^{0}$ is a scalar tetraquark $[bc][overline{u} overline{s}]$ built of a color-triplet diquark and an antidiquark, whereas $M$ is one of the vector mesons $rho ^{-}$, $K^{ast}(892)$, $D^{ast }(2010)^{-}$, and $D_{s}^{ast -}$. To calculate the partial widths of these decays, we use the QCD three-point sum rule approach and evaluate the weak transition form factors $G_{i}$ $(i=0,1,2,3)$, which govern these processes. The full width $Gamma _{mathrm{full}} =(12.9pm 2.1)times 10^{-8}~mathrm{MeV}$ and the mean lifetime $ tau=5.1_{-0.71}^{+0.99}~mathrm{fs}$ of the tetraquark $T_{b:overline{s}}^{ mathrm{AV}}$ are computed using the aforementioned weak decays. The obtained information about the parameters of $T_{b:overline{s}}^{mathrm{AV}}$ and $ mathcal{Z}_{b:overline{s}}^{0}$ is useful for experimental investigations of these double-heavy exotic mesons.
In this work we study the mass spectra of the fully-heavy tetraquark systems, i.e. $ccbar{c}bar{c}$, $bbbar{b}bar{b}$, $bbbar{c}bar{c}/ccbar{b}bar{b}$, $bcbar{c}bar{c}/ccbar{b}bar{c}$, $bcbar{b}bar{b}/bbbar{b}bar{c}$, and $bcbar{b}bar{c}$, within a potential model by including the linear confining potential, Coulomb potential, and spin-spin interactions. It shows that the linear confining potential has important contributions to the masses and is crucial for our understanding of the mass spectra of the fully-heavy tetraquark systems. For the fully-heavy tetraquarks $Q_1Q_2bar{Q}_3bar{Q}_4$ our explicit calculations suggest that no bound states can be formed below the thresholds of any meson pairs $(Q_1bar{Q}_3)$-$(Q_2bar{Q}_4)$ or $(Q_1bar{Q}_4)$-$(Q_2bar{Q}_3)$. Thus, we do not expect narrow fully-heavy tetraquark states to be existing in experiments.
In this work, we systematically study the mass spectrum of the fully heavy tetraquark in an extended chromomagnetic model, which includes both color and chromomagnetic interactions. Numerical results indicate that the energy level is mainly determined by the color interaction, which 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. The chromomagnetic interaction mixes the two color configurations and gives small splitting. The ground state is always dominated by the color-sextet configuration. We find no stable state below the lowest heavy quarkonium pair thresholds. Most states may be wide since they have at least one $S$-wave decay channel into two $S$-wave mesons. One possible narrow state is the $1^{+}$ $bbbar{b}bar{c}$ state with a mass $15719.1~text{MeV}$. It is just above the $eta_{b}bar{B}_{c}$ threshold. But this channel is forbidden because of the conservation of the angular momentum and parity.
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