Photon pair production in gluon fusion: top quark effects at NLO with threshold matching

Long Chen,Stephan Jahn,Stephen P. Jones,Johannes Schlenk,Matthias Kerner,Gudrun Heinrich,Hiroshi Yokoya

doi:10.1007/jhep04(2020)115

Abstract

We present a calculation of the NLO QCD corrections to the loop-induced production of a photon pair through gluon fusion, including massive top quarks at two loops, where the two-loop integrals are calculated numerically. Matching the fixed-order NLO results to a threshold expansion, we obtain accurate results around the top quark pair production threshold. We analyse how the top quark threshold corrections affect distributions of the photon pair invariant mass and comment on the possibility of determining the top quark mass from precision measurements of the diphoton invariant mass spectrum.

Highlights

The loop induced gg → γγ process enters as a next-to-next-to-leading order (NNLO) QCD correction to the pp → γγ cross section
We present a calculation of the NLO QCD corrections to the loop-induced production of a photon pair through gluon fusion, including massive top quarks at two loops, where the two-loop integrals are calculated numerically
The NNLO QCD corrections to pp → γγ have been calculated and implemented in MCFM in ref. [31], supplemented by the gg initiated loops proportional to nf at LO and NLO for five massless quark flavours, and at LO for massive top quark loops

Summary

Introduction

The loop induced gg → γγ process enters as a next-to-next-to-leading order (NNLO) QCD (order αs2) correction to the pp → γγ cross section. The process gg → γγ has been calculated at LO including both massless and massive quark loops in ref. The NLO QCD corrections to the gluon-fusion channel including massive top quark loops have become available [20], where the master integrals have been calculated numerically based on the numerical solution of differential equations [21, 22]. The NNLO QCD corrections to pp → γγ have been calculated and implemented in MCFM in ref. We provide an independent calculation of the QCD corrections to the process gg → γγ including massive top quark loops, confirming the results of ref.

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Results

Conclusion