Model-independent determination of |Vub|

The decay distribution of the kinematic variable ξu in inclusive charmless semileptonic decays of B mesons is unique. The novel method for a model-independent determination of |Vub| is described. To appear in Proceedings of the 3rd International Conference on B Physics and CP Violation Taipei, Taiwan, December 3-7, 1999 MODEL-INDEPENDENT DETERMINATION OF |Vub| CHANGHAO JIN School of Physics, University of Melbourne, Victoria 3010, Australia E-mail: [email protected] The decay distribution of the kinematic variable ξu in inclusive charmless semileptonic decays of B mesons is unique. The novel method for a model-independent determination of |Vub| is described. 1 Problems and Solutions The fundamental Cabibbo-Kobayashi-Maskawa (CKM) matrix element |Vub| has been determined from inclusive charmless semileptonic decays of B mesons, B → Xulν. However, there are experimental and theoretical problems that obstruct a precise determination of |Vub|. Experimentally, it is very difficult to separate signals from the rare B → Xulν decay from large B → Xclν background. Theoretically, QCD uncertainties arise in calculations that relate the measured quantity to |Vub|. The potential theoretical uncertainties from perturbative and nonperturbative QCD can be comparable. The solutions for the problems are provided by a novel method. It has been proposed to use the kinematic cut on the variable ξu = (q 0 + |q|)/MB (q is the momentum transfer to the lepton pair) above the kinematic limit for B → Xclν, ξu > 1−MD/MB, to separate B → Xulν signal from B → Xclν background. Most of B → Xulν events pass the above cut. This kinematic requirement provides a very efficient way for background suppression. |Vub| can then be extracted from the weighted integral of the measured ξu spectrum via the sum rule for inclusive charmless semileptonic decays of B mesons with little theoretical uncertainty. The sum rule is derived from the lightcone expansion and beauty quantum number conservation. Thus a modelindependent determination of |Vub| can be achieved, minimizing the overall (experimental and theoretical) error.