The midpoint between dipole and parton showers

TL;DR

This paper introduces a new parton-shower algorithm that combines ideas from dipole cascades and parton showers, featuring a simple evolution structure and a weighting method for negative splitting functions, with implementations in Pythia and Sherpa.

Contribution

It presents a novel parton-shower algorithm with a unique evolution variable and a weighting scheme, along with two independent implementations for major event generators.

Findings

Simplified analytic evolution structure.

Effective handling of negative splitting functions.

Public implementations in Pythia and Sherpa.

Abstract

We present a new parton-shower algorithm. Borrowing from the basic ideas of dipole cascades, the evolution variable is judiciously chosen as the transverse momentum in the soft limit. This leads to a very simple analytic structure of the evolution. A weighting algorithm is implemented, that allows to consistently treat potentially negative values of the splitting functions and the parton distributions. We provide two independent, publicly available implementations for the two event generators Pythia and Sherpa.