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

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## 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. Fig1.pdf [27 KiB] HiDef png [263 KiB] Thumbnail [219 KiB] 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. Fig2.pdf [18 KiB] HiDef png [114 KiB] Thumbnail [61 KiB] 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. Fig3.pdf [18 KiB] HiDef png [140 KiB] Thumbnail [138 KiB] Animated gif made out of all figures. PAPER-2018-038.gif Thumbnail

## Tables and captions

 Signal yields of the selected candidates. Table_1.pdf [44 KiB] HiDef png [76 KiB] Thumbnail [36 KiB] tex code Measured values of $\Delta_\Gamma$ and $y_{ C P }$ . The first uncertainty is statistical, the second is systematic. Table_2.pdf [51 KiB] HiDef png [31 KiB] Thumbnail [16 KiB] tex code

Created on 30 May 2020.