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T: Fachverband Teilchenphysik

T 94: Flavour Physics VI

T 94.2: Vortrag

Freitag, 20. März 2026, 09:15–09:30, KH 01.011

Search for B → D^(*) η ℓ ν at Belle II — •David Giesegh, Thomas Kuhr, and Thomas Lück — LMU Munich, Germany

Even though semileptonic B meson decays have been a field of intensive study over the past decades, there are still unresolved questions. One of these is the so-called gap problem, which describes a discrepancy between measurements of the inclusive semileptonic branching fraction and the sum of exclusive semileptonic branching fractions. This difference could be attributed to one or several as of yet unobserved decays, an example for which is B → D^(*) η ℓ ν, which is allowed within the Standard Model and commonly used in MC simulations of generic B meson decays to fill the gap.

In the analysis presented here we aim to measure this branching fraction for the first time using data collected by the Belle II Experiment. We leverage Belle II’s well known initial state kinematics to derive the angle between the decaying B meson and its visible daughters, which is used for signal extraction. Additionally, MVA methods are employed for candidate selection and background suppression, which is especially important in the reconstruction of η candidates. In the talk we will discuss the current status and future outlook of this analysis.

Keywords: Semileptonic B Decays; Flavour Physics; Belle II