# Measurement of $CP$ asymmetry in $D^0 \rightarrow K^- K^+$ and $D^0 \rightarrow \pi^- \pi^+$ decays

Abstract : Time-integrated $CP$ asymmetries in $D^0$ decays to the final states $K^- K^+$ and $\pi^- \pi^+$ are measured using proton-proton collisions corresponding to $3\mathrm{\,fb}^{-1}$ of integrated luminosity collected at centre-of-mass energies of $7\mathrm{\,Te\kern -0.1em V}$ and $8\mathrm{\,Te\kern -0.1em V}$. The $D^0$ mesons are produced in semileptonic $b$-hadron decays, where the charge of the accompanying muon is used to determine the initial flavour of the charm meson. The difference in $CP$ asymmetries between the two final states is measured to be \begin{align} \Delta A_{CP} = A_{CP}(K^-K^+)-A_{CP}(\pi^-\pi^+) = (+0.14 \pm 0.16\mathrm{\,(stat)} \pm 0.08\mathrm{\,(syst)})\% \ . \nonumber \end{align} A measurement of $A_{CP}(K^-K^+)$ is obtained assuming negligible $CP$ violation in charm mixing and in Cabibbo-favoured $D$ decays. It is found to be \begin{align} A_{CP}(K^-K^+) = (-0.06 \pm 0.15\mathrm{\,(stat)} \pm 0.10\mathrm{\,(syst)}) \% \ ,\nonumber \end{align} where the correlation coefficient between $\Delta A_{CP}$ and $A_{CP}(K^-K^+)$ is $\rho=0.28$. By combining these results, the $CP$ asymmetry in the $D^0\rightarrow\pi^-\pi^+$ channel is $A_{CP}(\pi^-\pi^+)=(-0.20\pm0.19\mathrm{\,(stat)}\pm0.10\mathrm{\,(syst)})\%$.
Document type :
Journal articles

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Submitted on : Tuesday, May 13, 2014 - 2:04:55 PM
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### Citation

R. Aaij, Y. Amhis, S. Barsuk, M. Borsato, O. Callot, et al.. Measurement of $CP$ asymmetry in $D^0 \rightarrow K^- K^+$ and $D^0 \rightarrow \pi^- \pi^+$ decays. Journal of High Energy Physics, Springer, 2014, 7, pp.041. ⟨10.1007/JHEP07(2014)041⟩. ⟨in2p3-00990286⟩

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