Final-state QED Multipole Radiation in Antenna Parton Showers

TL;DR

This paper develops a coherent QED parton shower formalism incorporating multipole photon radiation, maintaining a consistent 2 to 3 kinematic structure, and introduces a weighted spectator selection method to improve simulation performance.

Contribution

It presents a novel formalism for a fully coherent QED shower with multipole radiation, integrating a sector-based phase space division and a modified Sudakov algorithm.

Findings

Enhanced performance with weighted event generation

Formalism handles photon splitting similar to gluon splitting

Maintains on-shell 2 to 3 kinematic structure

Abstract

We present a formalism for a fully coherent QED parton shower. The complete multipole structure of photonic radiation is incorporated in a single branching kernel. The regular on-shell 2 to 3 kinematic picture is kept intact by dividing the radiative phase space into sectors, allowing for a definition of the ordering variable that is similar to QCD antenna showers. A modified version of the Sudakov veto algorithm is discussed that increases performance at the cost of the introduction of weighted events. Due to the absence of a soft singularity, the formalism for photon splitting is very similar to the QCD analogon of gluon splitting. However, since no color structure is available to guide the selection of a spectator, a weighted selection procedure from all available spectators is introduced.