Two Photon Decays of $\eta_c$ from Lattice QCD

TL;DR

This study uses lattice QCD to calculate the two-photon decay width of the eta_c meson, providing results that are smaller than previous quenched calculations and experimental data, with implications for understanding charmonium decays.

Contribution

First lattice QCD calculation of eta_c two-photon decay width using dynamical twisted mass fermions at multiple lattice spacings.

Findings

Decay width approximately 1.12 KeV in continuum limit

Results are smaller than previous quenched and experimental values

Errors are purely statistical

Abstract

We present an exploratory lattice study for the two-photon decay of $\eta_c$ using $N_f=2$ twisted mass lattice QCD gauge configurations generated by the European Twisted Mass Collaboration. Two different lattice spacings of $a=0.067$fm and $a=0.085$fm are used in the study, both of which are of physical size of 2$fm$. 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 $\Gamma\simeq 1.122(14)$KeV which is smaller than the previous quenched result and most of the current experimental results. Possible reasons are discussed.