Two-photon decay of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>X</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>6900</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math> from light-by-light scattering at the LHC

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