First-principle calculation of the gc! 2c decay width from lattice QCD

We perform a lattice QCD calculation of the gc! 2c 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 Nf 1/4 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 Cgccc 1/4 6.67o16 thorn stato6 thorn syst keV, which differs significantly from the Particle Data Group's reported value of Cgccc 1/4 5.4o4 thorn keV (2.9r tension). We provide insight into the comparison between our findings, previous theoretical predictions, and experimental measurements.(c) 2023 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.