On the normalization of unintegrated parton densities

TL;DR

This paper critiques existing definitions of unintegrated parton densities, proposes a modified normalization approach, and demonstrates that the new method resolves previous issues by integrating transverse momentum up to infinity.

Contribution

It introduces a modified KMRW UPDFs model that satisfies normalization conditions without the issues of previous definitions.

Findings

The modified UPDFs obey the normalization condition with infinite transverse momentum integration.

Previous issues with KMRW UPDFs are addressed and resolved.

The new approach improves the theoretical consistency of UPDFs.

Abstract

Recently, the definitions of the Kimber-Martin-Ryskin-Watt (KMRW) unintegrated parton densities (UPDFs) have been discussed by several groups. In the first part of this manuscript, we remind the issues encountered with these definitions and discuss the proposed solutions. In our opinion, none of these solutions is fully satisfactory. We observe that these issues seem to be related to the normalization condition where the UPDFs are related to the collinear PDFs by an integration over transverse momentum cut off by the factorization scale. Then, we build a modified version of the angular-ordering KMRW UPDFs, obeying the normalization condition with the transverse momentum integrated up to infinity and show that the usual issues are absent.