Speaker
Description
We study $gg\to\gamma\gamma$ amplitudes by including $t\bar t$ bound-state effects near their mass threshold. In terms of the non-relativistic expansion of the amplitude, the LO contribution is an energy-independent term in the one-loop amplitude, and a part of the NLO contribution is described by the non-relativistic Green function. We find that due to the interference of these terms, the diphoton mass spectrum shows a characteristic dip-and-bump shape near the threshold. In addition, the position of the dip and the bump is determined by the 1S mass of the $t\bar t$ resonance which is well predicted in terms of the short-distance mass of top-quark in NRQCD. Thanks to the simple and clean nature in its experimental measurement, it can give a superior method to determine the top-quark short-distance mass at hadron colliders.
