Measurement of the ratio of branching fractions and difference in $CP$ asymmetries of the decays $B^+\to J/\psi\pi^+$ and $B^+\to J/\psi K^+$

TL;DR

This paper measures the ratio of branching fractions and the difference in CP asymmetries between two B meson decays using LHCb data, providing the most precise estimate of CP violation in these processes to date.

Contribution

It presents the first precise measurement of the ratio of branching fractions and CP asymmetry difference for B+ decays to J/psi pi+ and K+ using 3 fb^-1 of LHCb data.

Findings

Branching fraction ratio is (3.83 ± 0.03 ± 0.03)×10^-2.

CP asymmetry difference is (1.82 ± 0.86 ± 0.14)×10^-2.

Most precise CP violation estimate in B+→J/ψπ+ decay to date.

Abstract

The ratio of branching fractions and the difference in $CP$ asymmetries of the decays $B^+\to J/\psi \pi^+$ and $B^+\to J/\psi K^+$ are measured using a data sample of $pp$ collisions collected by the LHCb experiment, corresponding to an integrated luminosity of $3~{{\,\mbox{fb}^{-1}}}$ at centre-of-mass energies of 7 and $8~\mathrm{\,Te\kern -0.1em V}$. The results are \begin{equation*} {\mathcal{B}(B^+\to J/\psi \pi^+)\over\mathcal{B}(B^+\to J/\psi K^+)}=(3.83\pm0.03\pm0.03)\times10^{-2}\,, \end{equation*} \begin{equation*} \mathcal{A}^{CP}(B^+\to J/\psi \pi^+)-\mathcal{A}^{CP}(B^+\to J/\psi K^+)=(1.82\pm0.86\pm0.14)\times10^{-2}, \end{equation*} where the first uncertainties are statistical and the second are systematic. Combining this result with a recent LHCb measurement of $\mathcal{A}^{CP}(B^+\to J/\psi K^+)$ provides the most precise estimate to date of $CP$ violation in the decay $B^+\to J/\psi \pi^+$, \begin{equation*} \mathcal{A}^{CP}(B^+\to J/\psi \pi^+) =(1.91\pm0.89\pm0.16)\times10^{-2}. \end{equation*}