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T: Fachverband Teilchenphysik

T 72: Flavour Physics IV

T 72.2: Talk

Thursday, March 19, 2026, 16:30–16:45, KH 01.011

Multivariate analysis of the rare decays B_(s)⁰ → µ⁺ µ⁻ in Run 3 at the LHCb experiment — Johannes Albrecht, Lukas Bertsch, Mick Mulder, •Katharina Popp, and Jan Peter Wagner — TU Dortmund University, Dortmund, Germany

Studies of the rare B_(s)⁰ → µ⁺ µ⁻ decays are core to the physics programme of the LHCb experiment, as they provide sensitivity to physics beyond the Standard Model. While the decay B_s⁰ → µ⁺ µ⁻ has been observed in the previous analyses using data from Run 2 of the LHC, the process B⁰ → µ⁺ µ⁻ is still to be observed. With the LHCb Upgrade I detector in Run 3, an upgraded strategy is required for the search for these processes. A major challenge arises from the amount of background events caused by random combinations of muons from b-hadron decays, which superimpose the signal processes. Thereby, a powerful tool for the suppression of combinatorial background is provided by considering the isolation of the final state muon tracks with respect to other tracks in the event. This aspect has already proven useful in previous analyses, where a combination of Boosted Decision Trees has been utilised. For the analysis with Run 3 data, the existing strategy for the suppression of combinatorial background is revisited and improvements are pursued, in order to enhance the signal significance of the decay B⁰ → µ⁺ µ⁻.

Keywords: Rare decays; LHCb Run 3; B physics; Flavour changing neutral currents