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

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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 $3 {{\, fb^{-1}}}$ at centre-of-mass energies of 7 and $8 \mathrm{\,TeV}$. 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*}

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Feynman diagrams for $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ ( K ^+ )$ decays at the tree (left) and one-loop (right) levels.

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Invariant mass distributions of (left) $ B ^- \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^- $ and (right) $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ $ candidates with the result of the fit superimposed, for data collected at (top) 7 TeV and (bottom) 8 TeV.

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Invariant mass distributions of (left) $ B ^- \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^- $ and (right) $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ candidates with the result of the fit superimposed, for data collected at (top) 7 TeV and (bottom) 8 TeV, where the $ B ^\pm \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^\pm $ contributions are neglected.

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Animated gif made out of all figures.

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Tables and captions

Signal yields and raw charge asymmetries determined from the fits, which are described in the text. The uncertainties are statistical.

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Relative systematic uncertainties ($\%$) for $\mathcal{R}_{\pi/K}$ and absolute systematic uncertainties ($\times10^{-2}$) for $\Delta {\mathcal{A}}^{\mathcal{C}_{P} } $. The uncertainties are quoted separately for the 7 and 8 TeV data. The dashes indicate negligible uncertainties (zero after rounding to two decimal places).

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Created on 09 December 2018.Citation count from INSPIRE on 09 December 2018.