Two Photon Decays of Charmonia from Lattice QCD

Abstract

We make the first calculation in lattice QCD of two-photon decays of mesons. Working in the charmonium sector, using the LSZ reduction to relate a photon to a sum of hadronic vector eigenstates, we compute form-factors in both the space-like and time-like domains for the transitions ${\eta }_c\to {\gamma }^{\ast }{\gamma }^{\ast }$ and ${\chi }_{c0}\to {\gamma }^{\ast }{\gamma }^{\ast }$. At the on-shell point we find approximate agreement with experimental world-average values.

Comments: Replaced with version to be published in PRL. Expanded discussion of possible systematic errors