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Measurement of $CP$ asymmetries in $D^{\pm}\rightarrow \eta^{\prime} \pi^{\pm}$ and $D_s^{\pm}\rightarrow \eta^{\prime} \pi^{\pm}$ decays

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Abstract

A search for $CP$ violation in $D^{\pm}\rightarrow \eta^{\prime} \pi^{\pm}$ and $D^{\pm}_{s}\rightarrow \eta^{\prime} \pi^{\pm}$ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of $3$ fb$^{-1}$, recorded by the LHCb experiment at centre-of-mass energies of $7$ and $8$ TeV. The measured $CP$-violating charge asymmetries are $A_{CP}(D^{\pm} \rightarrow \eta^{\prime} \pi^{\pm})=(-0.61\pm 0.72 \pm 0.53 \pm 0.12)\%$ and $A_{CP}(D^{\pm}_{s}\rightarrow \eta^{\prime} \pi^{\pm})=(-0.82\pm 0.36 \pm 0.22 \pm 0.27)\%$, where the first uncertainties are statistical, the second systematic, and the third are the uncertainties on the $A_{CP}(D^{\pm} \rightarrow K^0_S \pi^{\pm})$ and $A_{CP}(D^{\pm}_{s}\rightarrow \phi \pi^{\pm})$ measurements used for calibration. The results represent the most precise measurements of these asymmetries to date.

Figures and captions

Distribution of (a) $m(\pi ^+ \pi ^- \gamma)$ for $ D^{\pm}_{(s)} \rightarrow \eta'\pi ^\pm $ candidates. The grey solid area represents the signal region, while the black hatched area represents the $m(\pi ^+ \pi ^- \gamma)$ sideband. Distribution of (b) $m(\eta'\pi ^\pm )$ for $ D^{\pm}_{(s)} \rightarrow \eta'\pi ^\pm $ candidates in the $m(\pi ^+ \pi ^- \gamma)$ sideband.

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Mass distribution of $\eta^\prime\pi^\pm$ candidates, combined over all kinematic bins, $pp$ centre-of-mass energies, and hardware trigger selections, for (a) positively and (b) negatively charged $ D^{\pm}_{(s)}$ candidates. Points with errors represent data, while the curves represent the fitted model (solid), the $ D ^{\pm}_ s \rightarrow\phi_{3\pi}\pi ^\pm $ (dashed) and $ D ^\pm \rightarrow\phi_{3\pi}\pi ^\pm $ (long-dashed) components, and the sum of all background contributions (dotted), including combinatorial background. Residuals divided by the corresponding uncertainty are shown under each plot.

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Top: $ K ^0_{\mathrm{ \scriptscriptstyle S}} \pi ^\pm $ mass distribution for (a) positively and (b) negatively charged $ D ^\pm$ candidates. Bottom: $\phi \pi ^\pm $ mass distribution for (c) positively and (d) negatively charged $ D ^{\pm}_ s $ candidates. The signal regions are enclosed within the vertical dashed lines. The mass distributions are combined over all kinematic bins, $pp$ centre-of-mass energies, and hardware trigger selections.

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$\Delta\mathcal{A}_{\mathcal{C}_{P} }$ results for (a) $ D ^\pm \rightarrow\eta^\prime\pi ^\pm $ and (b) $ D ^{\pm}_ s \rightarrow\eta^\prime\pi ^\pm $ decays, as a function of $pp$ centre-of-mass energy and trigger selection. Uncertainties are statistical only. A shaded band representing the $68.3\%$ confidence intervals obtained from the weighted average over all the samples is shown to guide the eye.

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Tables and captions

Systematic uncertainties (absolute values in %) on $\Delta \mathcal{A}_{ C\!P }$ . The total systematic uncertainty is the sum in quadrature of the individual contributions.

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Supplementary Material [file]

Supplementary material full pdf

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This ZIP file contains supplemetary material for the publication LHCb-PAPER-2016-041. The files are: Supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps : The figures in variuous formats

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