An FONLL prescription with coexisting flavor number PDFs

TL;DR

This paper introduces a new FONLL-based method for incorporating heavy quark mass effects into PDFs, allowing for multiple heavy quark flavors and flexible theoretical accuracy, with practical code implementations.

Contribution

It proposes a novel prescription that explicitly uses coexisting PDFs with different active flavor numbers, improving the treatment of heavy quark effects in PDFs.

Findings

Allows simultaneous treatment of charm and bottom quark effects.

Generalizes to any fixed-order or resummed accuracy.

Provides code for deep inelastic scattering observables.

Abstract

We present a new prescription to account for heavy quark mass effects in the determination of parton distribution functions (PDFs) based on the FONLL scheme. Our prescription makes explicit use of the freedom to choose the number of active flavors at a given scale and, thus, use coexisting PDFs with different active flavor number. This new prescription is perturbatively equivalent to the former but improves the implementation in two ways. First, it can be naturally generalized to account simultaneously for multiple heavy quark effects, such as charm and bottom effects, which can both be relevant at the same scale due to the small mass difference. Second, it can be trivially generalized to use at any fixed-order or collinear resummed accuracy, while previous prescriptions required ad-hoc expansions of the DGLAP evolution kernels for each coefficient. We supplement the paper with codes for the computation of deep inelastic scattering observables in this new prescription.