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/psi pi(+) and B+ -> J/psi K+ 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/psi pi(+))/B(B+ -> J/psi K+) = (3.83 +/- 0.03 +/- 0.03) x 10(-2), A(CP)(B+ -> J/psi pi(+)) - A(CP)(B+ -> J/psi K+) = (1.82 +/- 0.86 +/- 0.14) x 10(-2), where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of A(CP)(B+ -> J/psi K+) provides the most precise estimate to date of CP violation in the decay B+ -> J/psi pi(+) A(CP)(B+ -> J/psi pi(+)) = (1.91 +/- 0.89 +/- 0.16) x 10(-2).