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T: Fachverband Teilchenphysik

T 63: Flavorphysik II

T 63.3: Vortrag

Mittwoch, 27. März 2019, 16:30–16:45, S15

Test of lepton flavour universality using the branching fraction ratio R_φ — •Simon Nieswand, Sarah Beranek, Christoph Langenbruch, Stefan Schael, and Eluned Smith — I. Physikalisches Institut, RWTH Aachen University

The LHCb detector at the LHC is designed for the search for New Physics (NP) beyond the Standard Model (SM) in heavy flavour decays. Particularly interesting are rare decays of b-hadrons that proceed via b → s transitions. In the SM, these flavour changing neutral currents are forbidden at tree-level. They can only occur at loop-level and can be influenced by heavy non-SM particles. Therefore, the branching fractions of decays like B_s⁰ → φ ℓ⁺ℓ⁻ are sensitive probes for NP.

Especially clean theory predictions are available for the ratios of rare semileptonic b → s decays with muons and electrons in the final state. Due to lepton universality, these ratios should be close to unity in the SM. The LHCb collaboration observed interesting tensions with the SM predictions for the ratios R_K^* and R_K corresponding to 2.4−2.5 and 2.6 standard deviations (σ), respectively. Therefore, it is interesting to study further rare B decays for a similar behavior.

In this talk the analysis strategy to measure the branching fraction ratio R_φ=B(B_s⁰ → φµ⁺µ⁻)/B(B_s⁰ → φ e⁺ e⁻) and the current status of the on-going analysis of the combined Run 1 and Run 2 LHCb data sample will be presented.