Strong Coupling Constant Determination from the new CTEQ-TEA Global QCD Analysis

TL;DR

This paper provides a new, precise determination of the strong coupling constant $oldsymbol{ ext{α}_s}$ from a comprehensive global QCD analysis incorporating recent high-precision LHC data, critically examining uncertainties and correlations.

Contribution

It introduces a robust framework for $oldsymbol{ ext{α}_s}$ extraction, addressing systematic uncertainties and proposing the concept of data-clustering safety for uncertainty estimates.

Findings

$oldsymbol{ ext{α}_s(M_Z)}=0.1183^{+0.0023}_{-0.0020}$ at 68% credibility

Demonstrates weak correlation between $oldsymbol{ ext{α}_s}$ and PDF functional forms

Highlights importance of data-clustering safety in uncertainty assessment

Abstract

We present a new determination of the strong coupling constant $\alpha_s$ from a global QCD analysis CT25 of parton distribution functions (PDFs) that incorporates high-precision experimental measurements from the Run-2 of the Large Hadron Collider together with a large sample of other measurements over a wide interval of energies. This work addresses two objectives: providing an up-to-date determination of $\alpha_s$ using NNLO calculations and a sensitive nucleon data set within a self-consistent framework, and critically assessing the robustness of the $\alpha_s(M_Z)$ extraction in light of systematic uncertainties as well as correlations of $\alpha_s(M_Z)$ with the functional forms of PDFs and other model parameters. In regard to the uncertainty assessment, we demonstrate that some commonly used criteria, including the dynamical tolerance and Bayesian hierarchical models, may produce significantly different or even unstable estimates for the net $\alpha_s$ uncertainty, and we introduce a concept of \textit{data-clustering safety} that the replicable uncertainty estimates must satisfy. Based on this in-depth examination of the CT25 global hadronic data set using a combination of analysis methods, and after demonstrating a weak correlation between $\alpha_s$ and the functional forms of CT25 PDF parametrizations, we find $\alpha_s(M_Z)=0.1183^{+0.0023}_{-0.0020}$ at the 68\% credibility level.