Search for B⁺_c→π⁺μ⁺μ⁻ decays and measurement of the branching fraction ratio B(B⁺_c→ψ(2S)π⁺)/B(B⁺_c→J/ψπ⁺)

The first search for nonresonant B⁺_c→π⁺μ⁺μ⁻ decays is reported. The analysis uses proton-proton collision data collected with the LHCb detector between 2011 and 2018, corresponding to an integrated luminosity of 9 fb⁻¹. No evidence for an excess of signal events over background is observed and an upper limit is set on the branching fraction ratio B(B⁺_c→π⁺μ⁺μ⁻)/B(B⁺_c→J/ψπ⁺)<2.1×10−4 at 90% confidence level. Additionally, an updated measurement of the ratio of the B⁺_c→ψ(2S)π⁺ and B⁺_c→J/ψπ⁺ branching fractions is reported. The ratio B(B⁺_c→ψ(2S)π⁺)/B(B⁺_c→J/ψπ⁺) is measured to be 0.254±0.018±0.003±0.005, where the first uncertainty is statistical, the second systematic, and the third is due to the uncertainties on the branching fractions of the leptonic J/ψ and ψ(2S) decays. This measurement is the most precise to date and is consistent with previous LHCb results.