Mattia Dalla Brida - High-precision determination of $\alpha_s$ from lattice QCD

Friday Jun 12, 2026, 11:00 AM → 1:00 PM Europe/Rome

Aula F (Via Della Vasca Navale 84)

The QCD coupling, $\alpha_s$, is a fundamental parameter of the Standard Model. It enters virtually every theoretical prediction for processes at the LHC and plays a central role in our understanding of electroweak vacuum stability, grand unified theories (GUTs), and searches for new coloured sectors beyond the Standard Model. Its current precision, approximately 0.8\% at the Z-boson mass scale, is expected to become a limiting factor for several precision measurements at future collider experiments. Achieving a determination well below the percent level is therefore highly desirable.
   
In this talk, I will present a recent determination of $\alpha_s$ that, for the first time, reaches a precision of about 0.5\% with fully controlled uncertainties. The result is based on a non-perturbative determination of the three-flavour QCD $\Lambda$-parameter, $\Lambda^{(3)}_{\rm QCD}$, obtained using lattice QCD methods. The effects of the charm and bottom quarks are subsequently incorporated through perturbative decoupling.   

I will discuss in detail the two independent strategies that have been pursued to determine $\Lambda^{(3)}_{\rm QCD}$, as well as the accuracy of perturbative decoupling in the inclusion of charm and bottom quark effects. 

By removing an important source of theoretical uncertainty, this determination of $\alpha_s$ has the potential to significantly improve the precision of analyses at current and future high-energy experiments. It will strengthen the prospects for uncovering subtle signatures of new physics and enable more stringent tests of the Standard Model.