In this seminar I will present the first simultaneous test of muon-electron universality in 𝐵+→𝐾+ℓ+ℓ− and 𝐵0→𝐾∗0ℓ+ℓ− decays, known as 𝑅(𝐾) and 𝑅(𝐾∗), in two regions of di-lepton invariant mass squared.
The analysis operates at a higher signal purity compared with previous analyses and implements a data-driven treatment of residual hadronic backgrounds. The analysis uses the full LHCb Run 1 and 2 data recorded in 2011-2012 and 2015-2018, corresponding to an integrated luminosity of 9 fb−1. This analysis is the most sensitive lepton universality test in rare b-decays and the results obtained supersede the previous LHCb measurements of 𝑅(𝐾) and 𝑅(𝐾∗0).
