Generation of central exclusive final states

TL;DR

This paper introduces a new scheme in Pythia 8 for generating central exclusive final states, enabling the study of higher order corrections and the impact of parton showers on such processes.

Contribution

The implementation of spin and colour decomposition in the initial-state shower allows for more accurate modeling of exclusive processes in Pythia 8.

Findings

Significant effects of parton showers on di-jet production.

Minor effects on central exclusive Higgs production.

Enhanced understanding of higher order corrections in exclusive processes.

Abstract

We present a scheme for the generation of central exclusive final states in the Pythia 8 program. The implementation allows for the investigation of higher order corrections to such exclusive processes as approximated by the initial-state parton shower in Pythia 8. To achieve this, the spin and colour decomposition of the initial-state shower has been worked out, in order to determine the probability that a partonic state generated from an inclusive sub-process followed by a series of initial-state parton splittings can be considered as an approximation of an exclusive colour- and spin-singlet process. We use our implementation to investigate effects of parton showers on some examples of central exclusive processes, and find sizeable effects on di-jet production, while the effects on e.g. central exclusive Higgs production are minor.