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Measurements of the branching fractions and $C P$ asymmetries of $B^{\pm} \to J / \psi \pi^{\pm}$ and $B^{\pm} \to \psi(2S) \pi^{\pm}$ decays

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Abstract

A study of B+ to J/psi pi+ and B+ to psi(2S) pi+ decays is performed with data corresponding to 0.37 fb-1 of proton-proton collisions at sqrt(s)=7 TeV. Their branching fractions are found to be B(B+ to J/psi pi+) = (3.88 +- 0.11 +- 0.15) x 10^{-5} and B(B+ to psi(2S) pi+) = (2.52 +- 0.26 +- 0.15) x 10^{-5}, where the first uncertainty is related to the statistical size of the sample and the second quantifies systematic effects. The measured CP asymmetries in these modes are ACP(J/psi pi) = 0.005 +- 0.027 +- 0.011 and ACP(psi(2S) pi) = 0.048 +- 0.090 +- 0.011 with no evidence of direct CP violation seen.

Figures and captions

Distribution of $\cos(\theta^*_h)$ versus the invariant mass of $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ $ candidates. The curved structure contains misidentified $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^+ $ decays which separate from the $ B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^+ $ vertical band for $\cos(\theta^*_h)<0$. The partially reconstructed background, $B\rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K\pi$ enters top left.

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Distributions of $ B ^\pm \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} h^{\pm}$ invariant mass, overlain by the total fitted PDF (thin line). Pion-like events, with DLL$_{K\pi}<6$ are reconstructed as $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^\pm $ and enter in the top plots. All other events are reconstructed as $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^\pm $ and are shown in the bottom plots on a logarithmic scale. $ B ^- $ decays are shown on the left, $ B ^+ $ on the right. The dark [red] curve shows the $ B ^\pm \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^\pm $ component, the light [green] curve represents $ B ^\pm \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^\pm $. The partially reconstructed contributions are shaded. In the lower plots these are visualised with a dark (light) shade for $ B ^0_ s $ ( $ B ^+$ or $ B ^0$ ) decays. In the top plots the shaded component are contributions from $ B \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} K ^\pm \pi$ (dark) and $ B \rightarrow { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu} \pi ^\pm \pi$ (light).

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Distributions of $ B ^\pm \rightarrow \psi {(2S)} h^{\pm}$ invariant mass. See the caption of Fig. 2 for details. The partially reconstructed background in the pion-like sample is present but negligible yields are found.

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Animated gif made out of all figures.

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Tables and captions

Signal shape parameters from the $ B ^\pm \rightarrow \psi h^{\pm}$ fits.

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Raw fitted yields. The labels `D' and `U' refer to the two polarities of the LHCb dipole.

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Summary of systematic uncertainties. The statistical fit errors are included for comparison.

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Created on 27 April 2024.