Some Dipole Shower Studies

TL;DR

This paper introduces a dipole-based initial-state parton shower model in PYTHIA, compares it with the traditional global-recoil approach, and demonstrates its excellent agreement with Deeply Inelastic Scattering data and matrix element calculations.

Contribution

It presents the first implementation of a dipole picture for initial-state radiation in PYTHIA, offering an alternative to the global-recoil strategy.

Findings

Dipole shower for initial-state radiation matches data well.

The dipole model agrees with matrix element calculations for the first branching.

Provides a viable alternative to the global-recoil approach in PYTHIA.

Abstract

Parton showers have become a standard component in the description of high-energy collisions. Nowadays most final-state ones are of the dipole character, wherein a pair of partons branches into three, with energy and momentum preserved inside this subsystem. For initial-state showers a dipole picture is also possible and commonly used, but the older global-recoil strategy remains a valid alternative, wherein larger groups of partons share the energy--momentum preservation task. In this article we introduce and implement a dipole picture also for initial-state radiation in PYTHIA, and compare with the existing global-recoil one, and with data. For the case of Deeply Inelastic Scattering we can directly compare with matrix element expressions and show that the dipole picture gives a very good description over the whole phase space, at least for the first branching.