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Measurement of CP asymmetries and branching fraction ratios of B$^{−}$ decays to two charm mesons

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Abstract

The $CP$ asymmetries of seven $B^-$ decays to two charm mesons are measured using data corresponding to an integrated luminosity of $9\text{ fb}^{-1}$ of proton-proton collisions collected by the LHCb experiment. Decays involving a $D^{*0}$ or $D^{*-}_s$ meson are analysed by reconstructing only the $D^0$ or $D^-_s$ decay products. This paper presents the first measurement of $\mathcal{A}^{CP}(B^- \rightarrow D^{*-}_s D^0)$ and $\mathcal{A}^{CP}(B^- \rightarrow D^{-}_s D^{*0})$, and the most precise measurement of the other five $CP$ asymmetries. There is no evidence of $CP$ violation in any of the analysed decays. Additionally, two ratios between branching fractions of selected decays are measured.

Figures and captions

Illustration of (left) tree, (centre) loop and (right) annihilation diagram contributions to the decay $ B ^- \rightarrow D ^- D ^0 $ in the SM. Similar diagrams, with the $ d $ quark replaced by an $ s $ quark, apply to the decay $ B ^- \rightarrow D ^-_ s D ^0 $ . These diagrams also apply to decays with excited charm mesons.

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Invariant-mass distribution of (top row) $ B ^- \rightarrow D ^-_ s D ^0 $ candidates, (middle row) $ B ^- \rightarrow D ^- D ^0 $ candidates and (bottom row) $ B ^- \rightarrow D ^{*-} D ^0 $ candidates, separated by charge into (left) $ B ^- $ and (right) $ B ^+ $ candidates. The fitted model described in the text is also drawn. The invariant-mass distributions of $ B \rightarrow D ^{**} D $ decays where the fitted yield is less than zero are not drawn.

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Animated gif made out of all figures.

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Tables and captions

Predictions in the SM (first four columns) and world average measurements (final column) of $ C P$ asymmetries for $ B ^- $ decays to two charm mesons in percent.

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Values of $ {\mathcal{A}}_{\mathrm{ raw}}$ , $ {\mathcal{A}}_{\mathrm{ P}}$ and $ {\mathcal{A}}_{\mathrm{ D}}$ in percent, averaged over all $ D ^0$ decay modes and data-taking periods. The uncertainties on $ {\mathcal{A}}_{\mathrm{ raw}}$ are statistical and systematic, respectively. The first uncertainty on $ {\mathcal{A}}_{\mathrm{ P}}$ contains all sources of uncertainty except that on $ {\mathcal{A}}^{ C P } ( B ^+ \rightarrow { J \mskip -3mu/\mskip -2mu\psi } K ^+ )$, which is the second uncertainty.

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Systematic uncertainties on the raw asymmetries in percent, averaged over all $ D ^0$ decay modes.

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Systematic uncertainties on the corrections for $ {\mathcal{A}}^{ C P }$ in percent, averaged over all $ D ^0$ decay modes.

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Relative systematic uncertainties on branching fraction ratios, in percent, averaged over all $ D ^0$ decay modes.

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Total correlations between the measured $ {\mathcal{A}}^{ C P }$ .

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$R( D ^- D ^0 / D ^-_ s D ^0 )/10^{-2}$ for each $ D ^0$ decay mode, for Run 1 and Run 2 and the combined measurement. The first uncertainty is statistical and the second is systematic.

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$R( D ^{*-} D ^0 / D ^- D ^0 )$ for each $ D ^0$ decay mode, for Run 1 and Run 2 and the combined measurement. The first uncertainty is statistical and the second is systematic.

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Supplementary Material [file]

Supplementary material full pdf

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supplementary.pdf contains supplementary tables for LHCb-PAPER-2023-007.

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Created on 02 May 2024.