A review of ‖ Vub‖ and ‖ Vcb‖ determinations

Abstract

Publisher Summary This chapter presents the status of experimental determinations of | V ub | and | V cb | elements in the Cabibbo–Kobayashi–Maskawa (CKM) mixing matrix. Such measurements, with small and well understood uncertainties, represent a key goal for the present heavy flavor physics program. The smallest quark mixing element,| V ub |, provides a bound on the upper vertex of one of the triangles representing the unitarity property of the CKM matrix and | V cb | represent the overall normalization. The statistical interpretation of these results will depend not only on the level of accuracy achieved but also on the possibility of properly defining probability density functions for their values. The determination of | V cb | is reaching a precision better than 1%. New approaches start allowing a determination of most of the input parameters directly from the data. The tests of operator product expansion (OPE) through moment analyses are also becoming available. The increasing ingenuity of experimentalists and phenomenologists in devising methods to measure | V ub | has brought individual accuracies to approach 15%. The overall consistency is encouraging for the perspectives of bringing | V ub | and | V cb | toward the domain of precision physics. Averaging inclusive and exclusive results can improve numerical accuracy because of partly uncorrelated uncertainties. A deeper understanding of the sources of systematic uncertainties and thorough checks of consistency to the level of the anticipated total accuracy will be required to validate the new frontier of accuracy.