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Register a new userDiscovery potential for the LHCb fully-charm tetraquark $X(6900)$ state via $bar{p}p$ annihilation reaction
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Inspired by the observation of the fully-charm tetraquark $X(6900)$ state at LHCb, the production of $X(6900)$ in $bar{p}prightarrow J/psi J/psi $ reaction is studied within an effective Lagrangian approach and Breit-Wigner formula. The numerical results show that the cross section of $X(6900)$ at the c.m. energy of 6.9 GeV is much larger than that from the background contribution. Moreover, we estimate dozens of signal events can be detected by D0 experiment, which indicates that searching for the $X(6900)$ via antiproton-proton scattering may be a very important and promising way. Therefore, related experiments are suggested to be carried out.
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The recently discovered fully charmed tetraquark candidate $X(6900)$ is analyzed within the frameworks of effective-range expansion, compositeness relation and width saturation, and a coupled multichannel dynamical study. By taking into account constraints from heavy-quark spin symmetry, the coupled-channel amplitude including the $J/psi J/psi,~ chi_{c0}chi_{c0}$ and $chi_{c1}chi_{c1}$ is constructed to fit the experimental di-$J/psi$ event distributions around the energy region near $6.9$ GeV. Another dynamical two-coupled-channel amplitude with the $J/psi J/psi$ and $psi(3770) J/psi$ is also considered to describe the same datasets. The three different theoretical approaches lead to similar conclusions that the two-meson components do not play dominant roles in the $X(6900)$. Our determinations of the resonance poles in the complex energy plane from the refined coupled-channel study are found to be consistent with the experimental analyses. The coupled-channel amplitudes also have another pole corresponding to a narrow resonance $X(6825)$ that we predict sitting below the $chi_{c0}chi_{c0}$ threshold and of molecular origin. We give predictions to the line shapes of the $chi_{c0}chi_{c0}$ and $chi_{c1}chi_{c1}$ channels, which could provide a useful guide for future experimental measurements.
Recently LHCb declared a new structure $X(6900)$ in the final state di-$J/psi$ which is popularly regarded as a $cc$-$bar cbar c$ tetraquark state. %popularly. Within the Bethe-Salpeter (B-S) frame we study the possible $cc$-$bar cbar c$ bound states and the interaction between diquark ($cc$) and antidiquark ($bar cbar c$). In this work $cc$ ($bar cbar c$) is treated as a color anti-triplet (triplet) axial-vector so the quantum numbers of $cc$-$bar cbar c$ bound state are $0^+$, $1^+$ and $2^+$. Learning from the interaction in meson case and using the effective coupling we suggest the interaction kernel for diquark and antidiquark system. Then we deduce the B-S equations for different quantum numbers. Solving these equations numerically we find the spectra of some excited states can be close to the mass of $X(6900)$ when we assign appropriate values for parameter $kappa$ introduced in the interaction (kernel).We also briefly calculate the spectra of $bb$-$bar bbar b$ bound states. Future measurement of $bb$-$bar bbar b$ state will help us to determine the exact form of effective interaction.
We have studied the masses for fully open-flavor tetraquark states $bcbar{q}bar{s}$ and $scbar{q}bar{b}$ with quantum numbers $J^{P}=0^{+},1^{+}$. We systematically construct all diquark-antiquark interpolating currents and calculate the two-point correlation functions and spectral densities in the framework of QCD sum rule method. Our calculations show that the masses are about $7.1-7.2$ GeV for the $bcbar{q}bar{s}$ tetraquark states and $7.0-7.1$ GeV for the $scbar{q}bar{b}$ tetraquarks. The masses of $bcbar{q}bar{s}$ tetraquarks are below the thresholds of $bar{B}_{s}D$ and $bar{B}_{s}^{*}D$ final states for the scalar and axial-vector channels respectively. The $scbar{q}bar{b}$ tetraquark states with $J^{P}=1^{+}$ lie below the $B_{c}^{+}K^{*}$ and $B_{s}^{*}D$ thresholds. Such low masses for these possible tetraquark states indicate that they can only decay via weak interaction and thus are very narrow and stable.
The s-channel annihilation of proton and antiproton into a neutral pion and a real or virtual photon followed by lepton pair emission is studied. Such mechanism is expected to play a role at moderate values of the total energy $sqrt{s}$, when the pion is emitted around $90^{circ}$ in the center of mass. A fair comparison with the existing data is obtained taking into account scattering and annihilation channels. The cross section is calculated and numerical results are given in the kinematical range accessible in the PANDA experiment at FAIR.
In the present work, we take the scalar, pseudoscalar, axialvector, vector and tensor (anti)diquark operators as the elementary constituents to construct vector four-quark currents without introducing explicit P-waves, and explore the mass spectrum of the vector hidden-charm tetraquark states via the QCD sum rules comprehensively, and revisit the assignments of the $Y$ states in the scenario of tetraquark states. The predicted vector hidden-charm tetraquark states can be confronted to the experimental data in the future.
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