We systematically explore the parametrization dependence of the Parton Distribution Functions (PDFs) to better quantify the true uncertainty from global QCD analyses. To achieve this, we employ a novel technique that automates the generation of polynomial parametrizations for PDFs using B\'ezier curves. This technique is implemented in a C++ module, named Fant\^omas, which is now included within the xFitter program. As an example, we examine the charged pion PDF. Our analysis reveals that the sea and gluon distributions in the pion are strongly correlated, and PDF solutions featuring a vanishing gluon and a large quark sea are still experimentally allowed.
@article{arxiv.2511.15657,
title = {Fant\^omas: An analysis of parton distributions in a pion with B\'ezier parametrizations},
author = {Lucas Kotz and Aurore Courtoy and Pavel Nadolsky and Fredrick Olness and Maximiliano Ponce-Chavez},
journal= {arXiv preprint arXiv:2511.15657},
year = {2025}
}
Comments
6 pages, 2 figures. Talk presented at the 32nd International Workshop on Deep Inelastic Scattering and Related Subjects (DIS 2025), Capetown, South Africa, 24-28 March 2025. To appear in the proceedings