Response to "Parton distributions need representative sampling"

TL;DR

This paper defends the NNPDF4.0 methodology against criticism, clarifying misconceptions about sampling and uncertainties, and demonstrating the robustness of the PDF results despite claims of inaccuracies.

Contribution

It provides a detailed rebuttal to criticisms of NNPDF4.0, clarifies the relationship between PDF central values and data fit minima, and demonstrates the validity of the methodology.

Findings

NNPDF4.0 sampling is faithful and robust.

The central PDF value does not always match the data fit minimum.

Similar PDFs with low probability are found in the NNPDF methodology.

Abstract

We respond to the criticism raised by Courtoy et al., in which the faithfulness of the NNPDF4.0 sampling is questioned and an under-estimate of the NNPDF4.0 PDF uncertainties is implied. We list, correct, and clarify in detail a number of inaccurate or misleading claims that are made in this Reference. Specifically, we explain and explicitly demonstrate why the central value of the PDF distribution does not generally coincide with the absolute minimum of the $\chi^{2}$ to the data. We examine some PDFs that have been constructed in the above study and claimed to be "good solutions": we show that similar PDFs are found with the NNPDF methodology, but with very low probability.