Multivariable evolution in parton showers with initial state partons

TL;DR

This paper extends parton shower models to include multiple scale variables, especially for initial state partons, improving the accuracy of simulations like Drell-Yan muon pair production.

Contribution

It introduces a multivariable evolution framework for initial state parton showers, enhancing the coordination with parton distribution functions and demonstrating advantages over traditional single-scale models.

Findings

Developed a three-scale variable example for parton showers.

Achieved better modeling of initial state radiation.

Provided results for Drell-Yan muon pair production.

Abstract

One can use more than one scale variable to define the family of surfaces in the space of parton splitting parameters that define the evolution of a parton shower. In an earlier paper, we developed this idea for electron-positron annihilation. Here, we use multiple scale variables for a parton shower with initial state partons. Then we need a more sophisticated analysis because the evolution of parton distribution functions must be coordinated with the parton shower evolution. We make the needed connections more precise than in our earlier work, even for the case of just one scale variable. Then we develop an example with three scale variables, which leads to advantages compared to the usual shower formulation with only one scale variable. We provide results for Drell-Yan muon pair production.