Speaker
Description
The strong coupling, $\alpha_s(m_Z)$, is a fundamental parameter of the Standard Model and its precise determination is of central importance to particle physics. It is ubiquitous in the description of hadron collider physics: its uncertainty directly affects the control of initial parton states, e.g. in $pp$-collisions at the LHC, and limits precision studies of Higgs boson production and decay rates. The high energy physics community has set the ambitious goal to reach per mille precision over the next 10-20 years.
A significant milestone is the precision result, $\alpha_s(m_Z)=0.11876(58)$, recently published by the ALPHA collaboration. It was obtained by combining two complementary methods to first determine the $\Lambda$-parameter in 3-flavour QCD, without relying on perturbation theory at low energies. Perturbation theory is used in the matching to 5-flavour QCD across the charm and bottom thresholds, with uncertainties estimated both perturbatively and non-perturbatively. The total error of 5 per mille is still statistics dominated and leaves some room for further improvement.