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T: Fachverband Teilchenphysik

T 42: Bottom-Quark: Produktion 1

T 42.1: Vortrag

Donnerstag, 1. März 2012, 16:45–17:00, ZHG 004

Semi-inclusive measurements of semileptonic B decays at Belle — •Phillip Urquijo — Universität Bonn, Bonn, Deutschland

Semileptonic B decays provide a precise environment for measuring the CKM parameters |V_ub| and |V_cb|, and for understanding the non-perturbative interactions of the b quark in the B meson. They are also a large background to measurements of rare leptonic B and semileptonic B_s decays. Much of the inclusive semileptonic B width is described by precise measurements of B → D^(*)ℓ ν decays. The remaining components are from higher multiplicity decays of B → D^(*) nπ ℓ ν, where n > 0 (referred to as D^** modes) and to a lesser extent B → D_s/Λ ℓ ν X, and Cabibbo suppressed modes. The sum of the exclusive modes does not saturate the full inclusive width, with 10-15% unaccounted for. This discrepancy is often assumed to be due to unmeasured resonant and non-resonant B → D^(*) nπ ℓ ν modes. The branching fractions of all D^** resonances have large uncertainties, with many modes still unmeasured due to limited kinematic phase space. Almost all semileptonic B decays involve a transition to D^(*)0, D^(*)+, and possibly D_s^(*)0 mesons, hence the relative abundance of these mesons in semileptonic B decays instructs us about the hadronic structure of semileptonic B decays. This study uses a new technique of characterising the semileptonic width by reconstructing semi-inclusive modes B → D_(s)^(*) X ℓ ν. This measurement is based on a data sample that contains 772 million B B pairs, collected by the Belle detector at KEKB.