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^+)-𝒜^CP(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 𝒜^CP(B^+→ J/ψ K^+) 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.