B-Meson Properties from Modified Sum Rule Analyses

We introduce two approaches to analyses of Borel sum rules. In the first method, we analyze the sum rules in the limit M2 → ∞. Here, the sum rules become very sensitive to the chosen threshold s0. We fix the threshold by setting the daughter sum rule equal to the meson mass in this limit. The second method introduces a Borel mass dependent threshold s0(M 2). We choose functions s0(M 2) such, that the corresponding sum rule is not dependent on M2 anymore. The relevant hadronic parameter is extracted at the most stable function s0(M 2). The two methods differ in the notion of quark-hadron duality. Whereas the first method emphasizes errors coming from the simple duality ansatz, the second method is constructed such as to extract hadronic properties from the region where the duality approximation is fulfilled best. We use these modifications of the sum rule approach to extract values for the B-meson decay constant fB, the semi-leptonic form factor f+(0) at zero momentum transfer and the strong coupling gB∗Bπ. The results coincide with other sum rule analyses.