Two-photon decays of $\eta _c$ from lattice QCD 后印本

摘要: We present an exploratory lattice study for the two-photon decay of ηc using Nf=2 twisted mass lattice QCD gauge configurations generated by the European Twisted Mass Collaboration. Two different lattice spacings of a=0.067fm and a=0.085fm are used in the study, both of which are of physical size of 2fm. The decay widths are found to be 1.025(5)KeV for the coarser lattice and 1.062(5)KeV for the finer lattice respectively where the errors are purely statistical. A naive extrapolation towards the continuum limit yields Γ≃1.122(14)KeV which is smaller than the previous quenched result and most of the current experimental results. Possible reasons are discussed.