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T: Fachverband Teilchenphysik

T 73: Flavour Physics IV

T 73.8: Talk

Thursday, April 3, 2025, 18:00–18:15, VG 1.103

Improving R(D^(*)) with hadronic FEI and leptonic tau decays with Belle II Run 1 data. — •Agrim Aggarwal, Florian Bernlochner, Markus Prim, Felix Metzner, and Ilias Ilias Tsaklidis — Physikalisches Institut der Rheinischen Friedrich-Wilhelms-Universität Bonn, Bonn, Germany

An important postulate of the Standard Model, which has been challenged by experimental measurements, is the assumption that all leptons couple identically to the electroweak gauge bosons. In this work, the expected precision of ratios R(D^*) = B(B → D^(*) τ ν_τ) / B(B → D^(*) ℓ ν_ℓ) are studied, a crucial test of lepton flavour universality, at Belle II. The Long Shutdown Run 1 (LS1) data at Belle II which corresponds to the total integrated luminosity of 365   fb⁻¹ is used. A technique known as hadronic tagging is employed to fully reconstruct one of the B mesons and furthermore the leptonic decays of τ lepton is considered. The ratios of interest are extracted using a two-dimensional binned maximum likelihood fit with a revised signal extraction strategy, implemented via pyhf, that enables a conceptually safer treatment of the systematic uncertainties handled using the package SysVar developed in Bonn.

Keywords: Lepton Flavour Universality; Belle II; New physics; revised signal extraction strategy; ratios $\mathrm{R}(D^{*})$