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Measurements of indirect CP asymmetries in $D^0\to K^-K^+$ and $D^0\to\pi^-\pi^+$ decays

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Abstract

A study of indirect CP violation in $D^0$ mesons through the determination of the parameter $A_\Gamma$ is presented using a data sample of $pp$ collisions, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected with the LHCb detector and recorded at the centre-of-mass energy of 7 TeV at the LHC. The parameter $A_\Gamma$ is the asymmetry of the effective lifetimes measured in decays of $D^0$ and $\bar{D}^0$ mesons to the CP eigenstates $K^-K^+$ and $\pi^-\pi^+$. Fits to the data sample yield $A_\Gamma(KK)=(-0.35\pm0.62\pm0.12)\times 10^{-3}$ and $A_\Gamma(\pi\pi)=(0.33\pm1.06\pm0.14)\times 10^{-3}$, where the first uncertainties are statistical and the second systematic. The results represent the world's best measurements of these quantities. They show no difference in $A_\Gamma$ between the two final states and no indication of CP violation.

Figures and captions

Fit of $\Delta m$ for one of the eight subsets, containing the $\overline{ D }{} ^0 \rightarrow K ^- K ^+ $ candidates with magnet polarity down for the earlier run period.

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(Top) Fit of decay time to $\overline{ D }{} ^0 \rightarrow K ^- K ^+ $ and corresponding pull plot for candidates with magnet polarity down for the earlier run period, where pull is defined as $({\rm data}-{\rm model})/{\rm uncertainty}$, and (middle and bottom) ratio of $\overline{ D }{} ^0$ to $ D ^0$ data and fit model for decays to $ K ^- K ^+ $ and $\pi ^- \pi ^+ $ for all data, respectively.

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ratio-KK-noPull.pdf
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ratio-pipi-noPull.pdf

Fits of $\ln(\chi^2_{\rm IP} )$ for $\overline{ D }{} ^0 \rightarrow K ^- K ^+ $ candidates for decay-time bins (left to right) $0.25-0.37 {\rm ps} $, $0.74-0.78 {\rm ps} $, and $1.55-1.80 {\rm ps} $.

KK_Dow[..].pdf [29 KiB]
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KK_Down_D0_D0bar_40000_FirstHalf_D0_lnIPChi2_bin0_nopull.pdf
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KK_Down_D0_D0bar_40000_FirstHalf_D0_lnIPChi2_bin10_nopull.pdf
KK_Dow[..].pdf [30 KiB]
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KK_Down_D0_D0bar_40000_FirstHalf_D0_lnIPChi2_bin20_nopull.pdf

Animated gif made out of all figures.

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Tables and captions

Systematic uncertainties, given as multiples of $10^{-3}$. The first column for each final state refers to the unbinned fit method and the second column to the binned fit method.

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tex code
Table_1.pdf

Supplementary Material [file]

Supplementary material full pdf

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Supplementary.pdf

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Created on 17 August 2019.Citation count from INSPIRE on 23 August 2019.