Erlangen 2026 – scientific programme

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T: Fachverband Teilchenphysik

T 94: Flavour Physics VI

T 94.6: Talk

Friday, March 20, 2026, 10:15–10:30, KH 01.011

R(D) and R(D*) Measurement using an Inclusive Tagging Method — •Fabio Novissimo¹, Tia Crane², Thomas Lück¹, and Thomas Kuhr¹ — ¹Ludwig-Maximilians-Universität München (LMU), München, Germany — ²DESY - Universität Hamburg

Lepton flavour universality (LFU) is a fundamental symmetry of the Standard Model (SM). This symmetry states that the three generations of leptons (electrons, muons and tauons), couple with equal strength to the W boson. Any deviation from this symmetry is a clear sign of new physics. In this regard, the semileptonic decays of B mesons are an invaluable portal for LFU tests. More specifically, the measurement of the ratios R(D) and R(D*) defined as

are two great ways to probe this symmetry, since the ratios allow many uncertainties to cancel and are predicted with a very high precision in the SM. Latest averaged results show that there is a 3.8σ tension with the SM prediction, making this measurements very relevant. The analysis presented in this talk aims to obtain an even more precise measurement of the ratios R(D) and R(D*) using Belle II data, and adopts an inclusive tagging approach, which allows increased statistics at the expenses of higher background levels. This talk will provide an overview of the analysis, as well as the current status and future outlook.

Keywords: Lepton flavour universality; B physics; Belle II; semileptonic