Lattice calculation of $\chi_{c0} \rightarrow 2\gamma$ decay width

TL;DR

This paper presents a lattice QCD calculation of the decay width of the $ ext{chi}_{c0}$ meson into two photons, using a model-independent approach across multiple lattice spacings, achieving results compatible with experimental data.

Contribution

The study introduces a novel, model-independent lattice QCD method to compute the $ ext{chi}_{c0} ightarrow 2 ext{gamma}$ decay width without momentum extrapolation, improving accuracy over previous approaches.

Findings

Decay width $ ightarrow$ 3.65 keV with uncertainties

Results agree with experimental data within 1.3$\sigma$

Method reduces systematic errors from momentum extrapolation

Abstract

We perform a lattice QCD calculation of the $\chi_{c0} \rightarrow 2\gamma$ 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 $\Gamma_{\gamma\gamma}(\chi_{c0})=3.65(83)_{\mathrm{stat}}(21)_{\mathrm{lat.syst}}(66)_{\mathrm{syst}}\, \textrm{keV}$. Albeit this large statistical error, our result is compatible with the experimental results within 1.3$\sigma$. Potential improvements of the lattice calculation in the future are also discussed.