SMuK 2023 – wissenschaftliches Programm

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T: Fachverband Teilchenphysik

T 129: Flavor X

T 129.4: Vortrag

Donnerstag, 23. März 2023, 18:15–18:30, HSZ/0304

Measurement of R(D^(*)) using B → D^(*)τν events with semileptonic tagging and leptonic τ decays — Florian Bernlochner, Jochen Dingfelder, Peter Lewis, and •Alina Manthei for the Belle II collaboration — Physikalisches Institut der Rheinischen Friedrich-Wilhelms-Universität Bonn

The Belle II experiment at the SuperKEKB asymmetric-energy collider, where electrons and positrons are collided at the Υ(4S) resonance, collects a large number of events with BB pairs. The analysis of semitauonic decays of these B mesons allows for tests of lepton flavour universality. Existing experimental results on the ratios of the branching fractions R(D) =B(B→ D τ⁻ ν) / B( B → Dℓ⁻ν) and R(D^*) =B(B→ D^* τ⁻ ν) / B(B^* → Dℓ⁻ν⁻), where ℓ denotes an electron or muon, are in tension with the Standard Model (SM) predictions, which might hint at physics beyond the SM, such as the presence of charged Higgs bosons or leptoquarks. A combined analysis of R(D) and R(D^*) with measurements from Belle, BaBar and LHCb yields a divergence from the SM prediction of >3σ. Thus, further investigations of these decays with the recently collected Belle II data are necessary. In order to exploit kinematic constraints in the BB decay, the second B meson in the event is reconstructed in semileptonic decay modes, a technique denoted as semileptonic tagging. In this talk, a signal extraction strategy for such a measurement will be presented and the current status and plans for the analysis will be outlined.