Speaker
Description
The strong coupling $\alpha_s(Q^2)$ represents one of the fundamental parameters of the Standard Model, and its precise determination is required a variety of phenomenological applications. We present an updated determination of $\alpha_s(m_Z)$ from the global NNPDF4.0 analysis carried out at approximated N$^3$LO (aN$^3$LO) accuracy, which also accounts for NLO QED corrections and the photon PDF, as well as for missing higher order uncertainties (MHOUs) for all processes considered. Our analysis is performed by means of two independent methodologies, the Correlated Replica Method and the Theory Covariance Method, yielding consistent results, and is extensively validated by closure tests where the underlying physical law is known. The latter provide the first closure test validation of $\alpha_s(m_Z)$ extractions from hadron collider data, and identify a number of potential pitfalls which may affect related determinations. In the baseline determination carried out at aN$^3$LO$_{\rm QCD}\otimes {\rm NLO}_{\rm QED}$ accuracy, we find $\alpha_s(m_Z)=0.1194 \pm 0.0007$ , consistent with the PDG average at the one-sigma level. We assess the perturbative convergence of our results, the role of QED corrections, the impact of MHOUs, and study their dependence on the input dataset. We also compare our determination with other recent extractions from PDF fits and from hadron collider data. Our result, with a total uncertainty of 0.6\%, provides one of the most precise determinations of the strong coupling obtained in the context of PDF fits.
