The Role of Different Schemes in the QCD Analysis and Determination of the Strong Coupling

TL;DR

This study performs a Next-to-Leading Order QCD analysis to evaluate how different schemes affect the determination of parton distribution functions and the strong coupling constant, showing scheme-dependent improvements in fit quality and parameter precision.

Contribution

It introduces a comparative analysis of the Thorne-Roberts and RT OPT schemes in NLO QCD, demonstrating improved accuracy and reduced uncertainties in PDFs and the strong coupling constant.

Findings

RT OPT scheme reduces PDF uncertainties, especially for gluons.

Switching schemes improves fit quality by up to 0.7%.

Strong coupling constant uncertainty decreases by up to 1.6%.

Abstract

In this article, we present a Next-to-Leading Order (NLO) QCD analysis to study the role and influence of different schemes on simultaneous determination of the Parton Distribution Functions (PDFs) and strong coupling, $\alpha_s(M^2_Z)$. We perform our analysis based on three different data sets, HERA I and II combined data, H1-ZEUS charm combined data, and H1 and ZEUS beauty production cross sections data, in two different Thorne-Roberts (TR or RT) and Thorne-Roberts Optimal (RT OPT) schemes. We show in going from RT scheme to RT OPT scheme, in addition of reduction the uncertainty of some PDFs, specially for the gluon distribution, we get $\sim 0.4$~\% and $\sim 0.7$~\%~improvement in the fit quality and $\sim 0.9$~\% and $\sim 1.6$~\%~improvement for the strong coupling, $\alpha_s(M^2_Z)$, without and with heavy flavor contributions, respectively.