Karlsruhe 2024 – scientific programme

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T: Fachverband Teilchenphysik

T 73: Flavour physics 3

T 73.5: Talk

Wednesday, March 6, 2024, 17:00–17:15, Geb. 30.41: HS 4

Inclusive analysis of untagged B → Xℓ⁺ℓ⁻ decays at Belle II — •Arul Prakash Sivagurunathan, Sviatoslav Bilokin, and Thomas Kuhr — Ludwig-Maximilians-Universität München

In recent years various deviations from the standard model expectation were observed in b → sℓ⁺ℓ⁻ measurements, dominated by exclusive studies. The combined deviations, while being large, are still not above the 5σ discovery threshold, partially owing to theoretical uncertainties. Precision measurements of inclusive B → Xℓ⁺ℓ⁻ decays can provide invaluable complementary information to scrutinize anomalies observed in their exclusive decay counterparts. However, limited tagging efficiency, small Standard Model signal and very high background rate make these measurements extremely challenging, with no results being published so far.

In our work, we will evaluate the chances of a 5σ result with data from the Belle and Belle II experiments. We will apply machine learning algorithms to tackle background rejection. We will finally compute the lepton flavour universality ratio R(X) = B(B → Xµ⁺µ⁻)/B(B → Xe⁺e⁻) which will be key to constrain potential New Physics contributions.

Keywords: Belle II; Rare decays; Penguin decays; Lepton flavour universality