Lattice calculation of $χ_{c0} \rightarrow 2γ$ decay width

We perform a lattice QCD calculation of the $χ_{c0} \rightarrow 2γ$ decay width using a model-independent method which does not require a momentum extrapolation of the corresponding off-shell form factors. The simulation is performed on ensembles of $N_f=2$ twisted mass lattice QCD gauge configurations with three different lattice spacings. After a continuum extrapolation, the decay width is obtained to be $Γ_{γγ}(χ_{c0})=3.65(83)_{\mathrm{stat}}(21)_{\mathrm{lat.syst}}(66)_{\mathrm{syst}}\, \textrm{keV}$. Albeit this large statistical error, our result is compatible with the experimental results within 1.3$σ$. Potential improvements of the lattice calculation in the future are also discussed.

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