Determining the strong coupling: status and challenges

Understand

The `XIIIth Quark Confinement and the Hadron Spectrum' conference (Confinement 2018) contained a `Round Table Discussion' on the status of the determinations of the strong coupling $\alpha_s(m_Z)$ as well as prospects for future improvements.

• In this contribution, we summarize the different aspects of the discussion.
• In particular, we cover $\alpha_s$ determinations from inclusive observables, such as the hadronic decays of the $Z$ boson and the $\tau$ lepton; from global fits of parton distribution functions (PDFs); from high-energy collider observables, and from event shapes; as well as from various observables computed by lattice QCD, specifically from the QCD static energy.
• There is overall good agreement between these various determinations, but there are also outliers, differing from the world average by up to $-5\%$.