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

Abstract

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

$$ \frac{\mathrm{\mathcal{B}}\left({B}^{+}\to J/\psi {\pi}^{+}\right)}{\mathrm{\mathcal{B}}\left({B}^{+}\to J/\psi {K}^{+}\right)}=\left(3.83\pm 0.03\pm 0.03\right)\times {10}^{-2}, $$

$$ {\mathcal{A}}^{\mathrm{CP}}\left({B}^{+}\to J/\psi {\pi}^{+}\right)-{\mathcal{A}}^{\mathrm{CP}}\left({B}^{+}\to J/\psi {K}^{+}\right)=\left(1.82\pm 0.86\pm 0.14\right)\times {10}^{-2}, $$

where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of ${\mathcal{A}}^{\mathrm{CP}}\left({B}^{+}\to J/{\psi K}^{+}\right)$ provides the most precise estimate to date of CP violation in the decay B ⁺ → J/ψπ ⁺,

$$ {\mathcal{A}}^{\mathrm{CP}}\left({B}^{+}\to J/{\psi \pi}^{+}\right)=\left(1.91\pm 0.89\pm 0.16\right)\times 1{0}^{-2}. $$