Coupled-channel interpretation of the LHCb double-$J/\psi$ spectrum and hints of a new state near the $J/\psi J/\psi$ threshold

Abstract

Recently, the LHCb Collaboration reported pronounced structures in the invariant mass spectrum of $J/\psi$-pairs produced in proton-proton collisions at the Large Hadron Collider. In this Letter, we argue that the data can be very well described within two variants of a coupled-channel approach employing $T$-matrices consistent with unitarity: (i) with just two channels, $J/\psi J/\psi$ and $\psi (2S)J/\psi$, as long as energy-dependent interactions in these channels are allowed, or (ii) with three channels $J/\psi J/\psi$, $\psi (2S)J/\psi$ and $\psi (3770)J/\psi$ with just constant contact interactions. Both formulations hint at the existence of a near-threshold state in the $J/\psi J/\psi$ system with the quantum numbers $J^{PC}=0^{++}$ or $2^{++}$, which we refer to as $X(6200)$. We suggest experimental tests to check the existence of this state and discuss what additional channels need to be studied experimentally to allow for distinctive tests between the two mechanisms proposed. If the molecular nature of the $X(6200)$, as hinted by the three-channel approach, is confirmed, many other double-quarkonium states should exist driven by the same binding mechanism. In particular, there should be an ${\eta }_c{\eta }_c$ molecule with a similar binding energy.

7 pages, 7 figures; typos corrected, results not affected

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• Some remarks on $X(6900)$
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• All-charm tetraquark in front form dynamics
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• Spectroscopy of all charm tetraquark states
• Going in quest of potential tetraquark interpretations for the newly observed $T_{\psi \psi }$ states in light of the diquark-antidiquark scenarios
• Hunting for tetraquarks in ultra-pheripheral heavy ion collisions
• Model independent analysis of coupled-channel scattering: a deep learning approach
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• Fully heavy pentaquark states in constituent quark model
• Triply-heavy tetraquarks in an extended relativized quark model
• The two-photon decay of X(6900) from light-by-light scattering at the LHC
• Improved understanding of the peaking phenomenon existing in the new di-$J/\psi$ invariant mass spectrum from the CMS Collaboration
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• Inclusive production of fully-charmed $1^{+-}$ tetraquark at $\mathbf{B}$ factory
• Pseudoscalar charmonium pair interactions via the Pomeron exchange mechanism
• Nature of the $X(6900)$ in partial wave decomposition of $J/\psi J/\psi$ scattering
• Perturbative QCD Evidence for Spin-2 Particles in the Di-$J/\psi$ Resonances
• Towards a precision determination of the $X(6200)$ parameters from data
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• Fully charmed P-wave tetraquark resonant states in the quark model
• Classification of Coupled-Channel Near-Threshold Structures
• Two-photon decay of fully-charmed tetraquarks from light-by-light scattering at the LHC
• Charmoniumlike Channels $1^{+}$ with Isospin $1$ from Lattice and Effective Field Theory
• Experimental Review of the Quarkonium Physics at the LHC
• Discovering an Unquenched Dynamics Mechanism for Charmonium Scattering
• Fully heavy tetraquark states with a diquark-antidiquark configuration
• ${\eta }_c{\eta }_c$ and $J/\psi J/\psi$ scatterings from lattice QCD
• All Heavy Tetraquarks: The Dynamical Diquark Model and Other Approaches
• Possible bound states in the triple-${\eta }_c$ and triple-$J/\psi$ systems
• Four-Charm-Quark Matter from the CMS Collaboration as a Witness of the Development of High-Precision Hadron Spectroscopy
• Hadronic molecules and multiquark states
• Decoding the near-threshold $X_{0,1}(4140)$ and $X_1(4685)$ states via OZI-suppressed coupled-channel scattering
• Systematic study of fully heavy-flavored tetraquarks $Q_1{Q}_2{\bar{Q}}_1{\bar{Q}}_2(Q_{1;2}\in \left\{b;c\right\})$: Mass spectra, threshold analysis, and confrontation with LHC data