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Measurement of $C P$ observables in $B^\pm \to D^{(*)} K^\pm$ and $B^\pm \to D^{(*)} \pi^\pm$ decays using two-body $D$ final states

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Abstract

Measurements of $C P$ observables in $B^\pm \rightarrow D^{(*)} K^\pm$ and $B^\pm \rightarrow D^{(*)} \pi^\pm$ decays are presented, where $D^{(*)}$ indicates a neutral $D$ or $D^*$ meson that is an admixture of meson and anti-meson states. Decays of the $D^*$ meson to the $D\pi^0$ and $D\gamma$ final states are partially reconstructed without inclusion of the neutral pion or photon. Decays of the $D$ meson are reconstructed in the $K^\pm \pi^\mp$, $K^+ K^-$, and $\pi^+ \pi^-$ final states. The analysis uses a sample of charged $B$ mesons produced in proton-proton collisions and collected with the LHCb experiment, corresponding to integrated luminosities of 2.0, 1.0, and 5.7 fb$^{-1}$ taken at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The measurements of partially reconstructed $B^\pm \to D^* K^\pm$ and $B^\pm \to D^* \pi^\pm$ with $D \to K^\mp \pi^\pm$ decays are the first of their kind, and a first observation of the $B^\pm \to (D \pi^0)_{D^*} \pi^\pm$ decay is made with a statistical significance of 6.1 standard deviations. All $C P$ observables are measured with world-best precision, and in combination with other LHCb results will provide strong constraints on the CKM angle $\gamma$.

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Legend indicating the invariant-mass fit components shown in Figs. ???$-$???.

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Invariant-mass distribution of selected $ B ^\pm \rightarrow [ K ^\pm \pi ^\mp ]_{D}h^{\pm}$ candidates. The result of the fit is shown by the solid navy line, and each component is listed in a legend provided in Fig. ???.

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Invariant-mass distribution of $ B ^\pm \rightarrow [ K ^\mp \pi ^\pm ]_D h^\pm$ candidates with the fit result overlaid. A legend is provided in Fig. ???.

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Invariant-mass distribution of $ B ^\pm \rightarrow [ K ^+ K ^- ]_D h^\pm$ candidates with the fit result overlaid. A legend is provided in Fig. ???.

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Invariant-mass distribution of $ B ^\pm \rightarrow [\pi ^+ \pi ^- ]_D h^\pm$ candidates with the fit result overlaid. A legend is provided in Fig. ???.

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Confidence regions for the (top row) $ B ^- \rightarrow D K ^- $ , (second row) $ B ^- \rightarrow D \pi ^- $ , (third row) $ B ^- \rightarrow D^* K ^- $ , and (fourth row) $ B ^- \rightarrow D^* \pi ^- $ fundamental parameters. The $ B ^- \rightarrow D h^-$ with $D \rightarrow K ^0_{\mathrm{S}} h^+ h^-$ contours from Ref. \cite{LHCb-PAPER-2020-019} are also overlaid.

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Animated gif made out of all figures.

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Tables and captions

The nine $ C P$ observables measured using $ B ^- \rightarrow D h^-$ decays, defined in terms of $B$ meson decay widths. Where indicated, $h^+h^-$ represents an average of the $D \rightarrow K ^+ K ^- $ and $D \rightarrow \pi ^+ \pi ^- $ modes. The $R$ observables represent partial width ratios and double ratios. The $A$ observables represent $ C P$ asymmetries.

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The 19 $ C P$ observables measured using $ B ^- \rightarrow D^* h^-$ decays, defined in terms of $B$ meson decay widths. Where indicated, $h^+h^-$ represents an average of the $D \rightarrow K ^+ K ^- $ and $D \rightarrow \pi ^+ \pi ^- $ modes. The $R$ observables represent partial width ratios and double ratios. The $A$ observables represent $ C P$ asymmetries. The $R_{K/\pi}^{K\pi,\gamma /\pi ^0 }$ observable is an average over the $D^* \rightarrow D \pi ^0 $ and $D^* \rightarrow D\gamma $ modes.

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Yields for the 24 signal modes.

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Statistical correlation matrix for $ B ^\pm \rightarrow D h^\pm$ observables.

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Systematic correlation matrix for $ B ^\pm \rightarrow D h^\pm$ observables.

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Statistical correlation matrix for $ B ^\pm \rightarrow D^* h^\pm$ observables.

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Systematic correlation matrix for $ B ^\pm \rightarrow D^* h^\pm$ observables.

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Supplementary Material [file]

Supplementary material full pdf

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Created on 19 February 2021.