QCD Parameters

• Applicant: Professor Dr. Hubert Spiesberger
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 261334331

Goal of this project is a timely determination of the fundamental parameters of quantum chromodynamics (QCD). New experimental measurements with high precision and new results from calculations of higher orders in perturbative QCD allow us to test our understanding of the theory of the strong interaction with higher accuracy and with more reliability. The higher precision also allows one to discover indirect hints for new physics from the observation of discrepancies between present day's experiments and theoretical predictions. Obviously, such an ambitious goal requires a precise knowledge of the parameters of the underlying theory. One of the most important parameters, the strong coupling constant, alphas, was and still is subject of extensive investigations. One of the most precise determinations of alphas relies on the knowledge of the total decay rate of tau leptons. Despite of the fact that higher-order corrections from perturbative QCD have been calculated to order alphas^4, different prescriptions for the resummation of leading logarithms by an application of the renormalization group equation can lead to differing results. The precision of such calculations is therefore not fully understood. In the proposed research project we want to study an approach to QCD adapted from similar investigations in the Standard Model of electroweak interactions. Instead of using alphas as expansion parameter of the perturbative series we want to use the decay rate of the $\tau$ lepton. This way, the perturbative expansion would become independent of the renormalization schemes and renormalization scales. Subject of the proposed research will also be other important parameters of QCD, in particular the masses of the u and d quarks, and the gluon condensate. Many previous attempts to determination quark masses were based on QCD sum rules, or on lattice QCD. Each of these approaches have their pro's and con's and it is important to perform alternative calculations in order to establish a consistent picture. The authors of this research proposal have developped, partly in collaboration with other groups of researchers, their own techniques for the application of QCD sum rules. With the help of these techniques it will be possible to extract precise information about QCD parameters and compare experimental results with theoretical predictions. The research program described in this proposal is planned for a collaboration between members of the University of Mainz and the group of Professor C. A. Dominguez at the University of Cape Town. Both groups work in the same field of the application of QCD to low-energy particle physics. The young South African scientists participating in the project come from population groups which were under-privileged under the Apartheid Regime.

• DFG Programme: Research Grants
• International Connection: South Africa
• Participating Persons: Professor Dr. Cesareo Dominguez; Professor Dr. Karl Schilcher