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arXiv · 2109.09381

First-principle calculation of $\eta_c\rightarrow 2\gamma$ decay width from lattice QCD

Yu Meng·Xu Feng·Chuan Liu·Teng Wang·Zuoheng Zou
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Abstract

We perform a lattice QCD calculation of the $\eta_c\to2\gamma$ decay width using a model-independent method that requires no momentum extrapolation of the off-shell form factors. This method also provides a straightforward and simple way to examine the finite-volume effects. The calculation is accomplished using $N_f=2$ twisted mass fermion ensembles. The statistically significant excited-state effects are observed and eliminated using a multi-state fit.The impact of fine-tuning the charm quark mass is also examined and confirmed to be well-controlled. Finally, using three lattice spacings for the continuum extrapolation, we obtain the decay width $\Gamma_{\eta_c\gamma\gamma}=6.67(16)_{\mathrm{stat}}(6)_{\mathrm{syst}}$ keV, which differs significantly from the Particle Data Group's reported value of $\Gamma_{\eta_c\gamma\gamma}=5.4(4)$ keV (2.9~$\sigma$ tension). We provide insight into the comparison between our findings, previous theoretical predictions, and experimental measurements.

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Yu Meng, Xu Feng, Chuan Liu, Teng Wang, Zuoheng Zou. 2021-09-20. First-principle calculation of $\eta_c\rightarrow 2\gamma$ decay width from lattice QCD. https://doi.org/10.1016/j.scib.2023.07.041

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