Photon Fragmentation in the Antenna Subtraction Formalism

TL;DR

This paper extends the antenna subtraction method to include photon fragmentation processes at NNLO in QCD, enabling more precise theoretical predictions for photon production at colliders.

Contribution

It introduces fragmentation antenna functions and phase space mappings for NNLO calculations involving photon fragmentation, advancing the antenna subtraction formalism.

Findings

Derived integrated forms of fragmentation antenna functions

Outlined construction principles for NNLO antenna subtraction with photons

Enabled application to various collider photon production processes

Abstract

The theoretical description of photon production at particle colliders combines direct photon radiation and fragmentation processes, which can not be separated from each other for definitions of photon isolation used in experimental measurements. The theoretical description of these processes must account for collinear parton-photon configurations, retaining the dependence on the photon momentum fraction, and includes the parton-to-photon fragmentation functions. We extend the antenna subtraction method to include photon fragmentation processes up to next-to-next-to-leading order (NNLO) in QCD. Collinear photon radiation is handled using newly introduced fragmentation antenna functions and associated phase space mappings. We derive the integrated forms of the fragmentation antenna functions and describe their interplay with the mass factorisation of the photon fragmentation functions. The construction principles of antenna subtraction terms up to NNLO for identified photons are outlined, thereby enabling the application of the method to different photon production processes at colliders.