Measurement of the ratio of the production cross sections times branching fractions of B_c^± → J/ψπ^± and B^± → J/ψK^± and B(B_c^± → J/ψπ^±π^±π^∓ / B(B_c^± → J/ψπ^±) in pp collisions at √s = 7 TeV

The ratio of the production cross sections times branching fractions (σ (B_c^±) B(B_c^± → J/ψπ^±) / (σ (B^±) B(B^± → J/ψK^±) is studied in proton-proton collisions at a center-of-mass energy of 7 TeV with the CMS detector at the LHC. The kinematic region investigated requires B_c^± and B^± mesons with transverse momentum p_π > 15 GeV and rapidity |y| < 1.6. The data sample corresponds to an integrated luminosity of 5.1 fb^-1. The ratio is determined to be [0.48 ± 0.05 (stat) ± 0.03(syst) ± 0.05 (τ_Bc)]%. The B_c^± → J/ψπ^±π^±π^∓ decay mode is also observed in the same data sample. Using a model-independent method developed to measure the efficiency given the presence of resonant behaviour in the three-pion system, the ratio of the branching fractions B(B_c^± → J/ψπ^±π^±π^∓) /B(B_c^± → J/ψπ^±) is measured to be 2.55 ± 0.80(stat) ± 0.33(syst)_-0.01 ^+0.04 (τ_Bc), consistent with the previous LHCb result.