LePDF: Standard Model PDFs for High-Energy Lepton Colliders

TL;DR

This paper develops and provides first-principles derived Parton Distribution Functions for leptons, accounting for Standard Model interactions, to improve predictions for high-energy lepton collider experiments.

Contribution

It numerically solves DGLAP equations for LePDFs at double-log order and releases public PDFs including polarization effects for muons and electrons.

Findings

LePDFs differ significantly from the Effective Vector Approximation at small momentum fractions.

The work provides publicly available LePDFs for muons and electrons, facilitating collider physics analyses.

Polarization effects are incorporated into the LePDFs, enhancing their accuracy.

Abstract

The emission of collinear radiation off an elementary lepton can be factorised from the hard scattering process by introducing Parton Distribution Functions of a Lepton (LePDF), which, contrary to protons, can be derived from first principles. In case of multi-TeV lepton colliders, such as the muon colliders currently being proposed, the complete structure of Standard Model interactions must be taken into account. In this work we solve numerically the corresponding DGLAP equations at the double-log order and provide public files with LePDFs for both muons and electrons, including polarisation effects. We discuss several interesting aspects of the resulting PDFs and compare them with the Effective Vector Approximation, showing that the latter fails to describe well the vector bosons PDFs at small momentum fractions, unless it is extended to higher orders.