The two-photon decay of X(6900) from light-by-light scattering at the LHC

Abstract

The LHCb Collaboration has recently discovered a structure around 6.9 GeV in the double-$J/\psi$ mass distribution, possibly a first fully-charmed tetraquark state $X(6900)$. Based on vector-meson dominance (VMD) such a state should have a significant branching ratio for decaying into two photons. We show that the recorded LHC data for the light-by-light scattering may indeed accommodate for such a state, with a $\gamma \gamma$ branching ratio of order of $10^{-4}$, which is larger even than the value inferred by the VMD. The spin-parity assignment $0^{-+}$ is in better agreement with the VMD prediction than $0^{++}$, albeit not significantly at the current precision. Further light-by-light scattering data in this region, clarifying the nature of this state, should be obtained in the Run 3 and probably in the high-luminosity phase of the LHC (Run 4 etc.).

arXiv comment6 pages, 4 figures

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• Going in quest of potential tetraquark interpretations for the newly observed $T_{\psi \psi }$ states in light of the diquark-antidiquark scenarios
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• Exciting Ions: a Systematic Treatment of Ultraperipheral Heavy Ion Collisions with Nuclear Breakup
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