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Measurement of the Charm-mixing parameter $y_{C\!P}$

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Information

Abstract

A measurement of the charm-mixing parameter $y_{CP}$ using $D^0 \to K^+ K^-$, $D^0 \to \pi^+ \pi^-$, and $D^0 \to K^- \pi^+$ decays is reported. The $D^0$ mesons are required to originate from semimuonic decays of $B^-$ and $\overline{B}^0$ mesons. These decays are partially reconstructed in a data set of proton-proton collisions at center-of-mass energies of 7 and 8 TeV collected with the LHCb experiment and corresponding to an integrated luminosity of 3 fb$^{-1}$. The $y_{CP}$ parameter is measured to be $(0.57 \pm 0.13(\rm{stat.}) \pm 0.09(\rm{syst.}))\%$, in agreement with, and as precise as, the current world-average value.

Figures and captions

Distribution of $ D ^0$ mass for candidates passing the selection with fit projections overlaid: (top) $ D ^0 \rightarrow K^+K^-$ decays, (center) $ D ^0 \rightarrow \pi^+\pi^-$ decays, and (bottom) $ D ^0 \rightarrow K^-\pi^+$ decays.

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Ratio of decay-time acceptances from simulation for (top) $ D ^0 \rightarrow K^+K^-$ over $ D ^0 \rightarrow K^-\pi^+$ decays and (bottom) $ D ^0 \rightarrow \pi^+\pi^-$ over $ D ^0 \rightarrow K^-\pi^+$ decays.

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Acceptance-corrected signal-yield ratio of (top) $ D ^0 \rightarrow K^+K^-$ over $ D ^0 \rightarrow K^-\pi^+$ decays and (bottom) $ D ^0 \rightarrow \pi^+\pi^-$ over $ D ^0 \rightarrow K^-\pi^+$ decays as a function of $ D ^0$ decay time, with fit projection overlaid.

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Animated gif made out of all figures.

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Tables and captions

Signal yields of the selected candidates.

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Measured values of $\Delta_\Gamma$ and $ y_{ C P }$ . The first uncertainty is statistical, the second is systematic.

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Created on 30 May 2020.