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Search for $CP$ violation in $D^{\pm}\rightarrow K^0_S K^{\pm}$ and $D^{\pm}_{s}\rightarrow K^0_S \pi^{\pm}$ decays

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Abstract

A search for \CP violation in Cabibbo-suppressed $D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}$ and $D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}$ decays is performed using $pp$ collision data, corresponding to an integrated luminosity of 3 fb$^{-1}$, recorded by the LHCb experiment. The individual $CP$-violating asymmetries are measured to be \begin{eqnarray*} \mathcal{A}_{CP}^{D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}} & = & (+0.03 \pm 0.17 \pm 0.14) \% \mathcal{A}_{CP}^{D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}} & = & (+0.38 \pm 0.46 \pm 0.17) \%, \end{eqnarray*} assuming that $CP$ violation in the Cabibbo-favoured decays is negligible. A combination of the measured asymmetries for the four decay modes $D^{\pm}_{(s)}\rightarrow K^0_{\mathrm{S}} K^{\pm}$ and $D^{\pm}_{(s)}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}$ gives the sum \[ \mathcal{A}_{CP}^{D^{\pm}\rightarrow K^0_{\mathrm{S}} K^{\pm}} + \mathcal{A}_{CP}^{D^{\pm}_{s}\rightarrow K^0_{\mathrm{S}} \pi^{\pm}} = (+0.41 \pm 0.49 \pm 0.26) \%. \] In all cases, the first uncertainties are statistical and the second systematic. The results represent the most precise measurements of these asymmetries to date and show no evidence for CP violation.

Figures and captions

Invariant mass distributions for the a) $ D ^+ _{(s)} \rightarrow K ^0_{\rm\scriptscriptstyle S} \pi ^+ $ , b) $ D ^- _{(s)} \rightarrow K ^0_{\rm\scriptscriptstyle S} \pi ^- $ , c) $ D ^+ _{(s)} \rightarrow K ^0_{\rm\scriptscriptstyle S} K ^+ $ and d) $ D ^- _{(s)} \rightarrow K ^0_{\rm\scriptscriptstyle S} K ^- $ decay candidates for data taken in the magnetic polarity {\it Up} configuration at $\sqrt{s}=8$ TeV. The data are shown as black points and the total fit function by a blue line. The contributions from the signal and the low-mass, cross-feed and combinatorial backgrounds are indicated by red (dotted), green (full), magenta (dash-dotted) and black (multiple-dot-dashed) lines, respectively. The bottom figures are the normalised residuals (pull) distributions.

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Invariant mass distributions for the a) $ D ^+ _{(s)} \rightarrow \phi \pi ^+ $ and b) $ D ^- _{(s)} \rightarrow \phi \pi ^- $ decay candidates for data taken in the magnet polarity {\it Up} configuration at $\sqrt{s}=8$ TeV. The data are shown as black points and the total fit function by a blue line. The contributions from the signal and the low-mass and combinatorial backgrounds are indicated by red (dotted), green (full) and black (multiple-dot-dashed) lines, respectively. The bottom figures are the normalised residuals (pull) distributions.

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Tables and captions

Signal yields.

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Measured asymmetries (in %) for the decay modes $ D ^\pm \rightarrow K ^0_{\rm\scriptscriptstyle S} \pi ^\pm $ , $ D ^{\pm}_ s \rightarrow K ^0_{\rm\scriptscriptstyle S} \pi ^\pm $ , $ D ^{\pm}_ s \rightarrow K ^0_{\rm\scriptscriptstyle S} K ^\pm $ and $ D ^{\pm}_ s \rightarrow \phi \pi ^\pm $ and the calculated $ C\!P$ asymmetries. The results are reported separately for $\sqrt{s}=7$ TeV and $\sqrt{s}=8$ TeV data and the two magnetic polarities ({\it Up} and {\it Down}). The combined results are given in the final column. The quoted uncertainties are statistical only.

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Systematic uncertainties (absolute values in %) on the $ C\!P$ asymmetries for $\sqrt{s}=7$ and $8$ TeV data. The total systematic uncertainty is the sum in quadrature of the individual contributions.

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Supplementary Material [file]

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Created on 17 December 2018.Citation count from INSPIRE on 18 December 2018.