# Subproject B2: Lattice computation of input parameters of perturbative QCD

Project leader:

Prof. Dr. Ulrich Wolff, Institute of Physics, Humboldt-University of Berlin

In order to test QCD as the theory of strong interactions its predictions have to be worked out and compared with experiments. At high energies this is done using perturbation theory. Here a variety of experimental results is expressed in terms of only a few quantities, namely the energy-dependent strong coupling constant and the quark mass parameters. By now lattice discretisation and numerical simulations are well established as the tools of choice for the extraction of e.g. the mass spectrum or certain matrix elements.

If we can master QCD on all energy scales these aspects can be connected by calculating the high-energy parameters in terms of of the spectral parameters instead of treating them as adjustable input to perturbation theory. This problem, which due to the existence of different energy scales is very sophisticated, is addressed in the project B2.

This is done with the use of a special finite-size-scaling technique, which -- including improvement -- has been developed by the ALPHA collaboration over the last decade. It has been refined by experiences made in the quenched and two-flavor approximations. In the present stage we have first results for the scale evolution with four flavors and will now move to make the calculation fully realistic.

The next goals of the project are:

- Finalization of the over-all scale setting at two flavors
- Refined continuum extrapolation of the running coupling and quark-masses in the massless four flavor scheme
- Over-all scale setting four 2+1+1 flavors
- Controlled approximate inclusion of heavy quarks
- Lambda parameter and light quark masses in the five flavor theory

Last Change: June, 15^{th} 2011