Top-quark effects in diphoton production through gluon fusion at NLO in QCD

Abstract

Diphoton production is one important channel at hadron colliders. Gluon fusion into diphoton via quark loops provide a substantial contribution. When the top quark mediated contribution is negligible below the top pair threshold, it becomes important at the threshold and above. We present the first complete computation of the next-to-leading order(NLO) corrections to this pro- cess, including contributions from the top quark. The analytical expression for relevant two-loop diagrams are unknown and we developed a numerical algorithm to compute them. We found that NLO corrections is large over all kinematic regions. The top quark contribution leads to change of slope below and above the top pair threshold, and it is more visible at NLO. We further find that above the top quark threshold, NLO corrections is larger after including the top quark contribution.