Measurement of the ratio of branching fractions and difference in CP asymmetries of the decays B+ → J/ψπ+ and B+ → J/ψK+

The ratio of branching fractions and the difference in CP asymmetries of the decays B+ → J/ψπ+ and B+ → J/ψK+ are measured using a data sample of pp collisions collected by the LHCb experiment, corresponding to an integrated luminosity of 3 fb−1 at centre-of-mass energies of 7 and 8 TeV. The results are B(B+ → J/ψπ+) B(B+ → J/ψK+) = (3.83 ± 0.03 ± 0.03) × 10−2 , A CP(B + → J/ψπ+) − ACP(B + → J/ψK+) = (1.82 ± 0.86 ± 0.14) × 10−2 , where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of ACP(B+ → J/ψK+) provides the most precise estimate to date of CP violation in the decay B+ → J/ψπ+, A CP(B + → J/ψπ+) = (1.91 ± 0.89 ± 0.16) × 10−2 .