The strong coupling αs is the most important parameter of Quantum Chromodynamics (QCD) therefore it is essential to determine it with high precision. This work presents an improved approach for extracting αs comparing the numerical results of lattice QCD simulations to the perturbative expansion of the QCD static energy. We apply R-improvement to its 3-loop fixed-order prediction, enabling the subtraction of the u=1/2 renormalon and the corresponding summation of large logarithms. We also perform resummation of large ultra-soft logs to N³LL accuracy using renormalization group equations. A new and more flexible parametrization of the renormalization scale has been implemented, allowing us to extend perturbation theory to distances of the order of 0.5 fm. Perturbative uncertities are estimated randomly varying the parameters that specify the renormalization scale. Performing R-evolution in different subtraction schemes such as the MSR, the PS mass, and the RS mass, we show that the extracted value of αs is strongly correlated to the prediction for the leading renormalon normalization. Finally, we combine Lattice data from different simulations into a single dataset, thus simplifying the fitting procedure. Using this approach, we determine the strong coupling with a precision comparable to that of the world average.
José Manuel Mena Valle (Salamanca): A precise αs determination from the R-improved QCD Static Energy
