Nonperturbative QCD in Heavy-Quark Systems

The project aims at the theoretical analysis of the effects of strong interactions in weak processes with hadrons containing the heavy beauty quark b. Weak interactions of the b quark give a possibility to probe a fundamental property of nature - the difference between matter and antimatter, known as CP violation. They also allow a measurement of the unknown parameters of the Standard Model describing the mixing between the heavy and the light quarks, and open a window to physics beyond the Standard Model. In order to test the Standard Model in b- physics experiments, one needs to separate the relatively simple weak interactions of the b quark from its complicated strong interactions. The latter are related to the confinement of the b quark in a hadron and are the subject of nonperturbative quantum chromodynamics (QCD). The nonperturbative QCD effects pose the main difficulty for the theoretical description of weak processes with beauty hadrons. At the same time, experiments on weak decays of heavy hadrons provide important information on the hadron structure and on QCD in the nonperturbative domain. In spite of the great progress in the theoretical study of nonperturbative QCD effects in heavy-quark systems, a dramatic increase of the oncoming data demands a higher accuracy of the theoretical predictions. The novel feature of this project is the combination of several methods for nonperturbative QCD. The basis for our analysis is provided by the recently demonstrated correspondence between QCD sum rules and effective constituent-quark models, which opens two promising possibilities: 1. This correspondence can give a firm QCD basis for the constituent quark picture, which is essentially the only method to treat the full hadron spectrum and excited states. 2. It prompts the improvements of QCD sum rules and, in particular, it opens a possibility to find the optimal choice of the QCD sum-rule parameters for heavy-quark systems. The results from the optimised QCD sum-rule analysis will be used to control the chiral and heavy-quark extrapolations necessary for treating beauty hadrons in lattice QCD. As a result, we expect considerable improvements of the predictions from all these methods.

The project aims at the theoretical analysis of the effects of strong interactions in weak processes with hadrons containing the heavy beauty quark b. Weak interactions of the b quark give a possibility to probe a fundamental property of nature - the difference between matter and antimatter, known as CP violation. They also allow a measurement of the unknown parameters of the Standard Model describing the mixing between the heavy and the light quarks, and open a window to physics beyond the Standard Model. In order to test the Standard Model in b- physics experiments, one needs to separate the relatively simple weak interactions of the b quark from its complicated strong interactions. The latter are related to the confinement of the b quark in a hadron and are the subject of nonperturbative quantum chromodynamics (QCD). The nonperturbative QCD effects pose the main difficulty for the theoretical description of weak processes with beauty hadrons. At the same time, experiments on weak decays of heavy hadrons provide important information on the hadron structure and on QCD in the nonperturbative domain. In spite of the great progress in the theoretical study of nonperturbative QCD effects in heavy-quark systems, a dramatic increase of the oncoming data demands a higher accuracy of the theoretical predictions. The novel feature of this project is the combination of several methods for nonperturbative QCD. The basis for our analysis is provided by the recently demonstrated correspondence between QCD sum rules and effective constituent-quark models, which opens two promising possibilities: 1. This correspondence can give a firm QCD basis for the constituent quark picture, which is essentially the only method to treat the full hadron spectrum and excited states. 2. It prompts the improvements of QCD sum rules and, in particular, it opens a possibility to find the optimal choice of the QCD sum-rule parameters for heavy-quark systems. The results from the optimised QCD sum-rule analysis will be used to control the chiral and heavy-quark extrapolations necessary for treating beauty hadrons in lattice QCD. As a result, we expect considerable improvements of the predictions from all these methods.