Measurement of CP asymmetries in $ {D}_{(s)}^{+}\to \eta {\pi}^{+} $ and $ {D}_{(s)}^{+}\to {\eta}^{\prime }{\pi}^{+} $ decays

Searches for CP violation in the decays $ {D}_{(s)}^{+}\to \eta {\pi}^{+} $ and $ {D}_{(s)}^{+}\to {\eta}^{\prime }{\pi}^{+} $ are performed using pp collision data corresponding to 6 fb$^{−1}$ of integrated luminosity collected by the LHCb experiment. The calibration channels $ {D}_{(s)}^{+}\to \phi {\pi}^{+} $ are used to remove production and detection asymmetries. The resulting CP-violating asymmetries are$ {\displaystyle \begin{array}{l}{\mathcal{A}}^{CP}=\left({D}^{+}\to \eta {\pi}^{+}\right)=\left(0.34\pm 0.66\pm 0.16\pm 0.05\right)\%,\\ {}{\mathcal{A}}^{CP}=\left({D}_s^{+}\to \eta {\pi}^{+}\right)=\left(0.32\pm 0.51\pm 0.12\right)\%,\\ {}\begin{array}{l}{\mathcal{A}}^{CP}=\left({D}^{+}\to {\eta}^{\prime }{\pi}^{+}\right)=\left(0.49\pm 0.18\pm 0.06\pm 0.05\right)\%,\\ {}{\mathcal{A}}^{CP}=\left({D}_s^{+}\to {\eta}^{\prime }{\pi}^{+}\right)=\left(0.01\pm 0.12\pm 0.08\right)\%,\end{array}\end{array}} $where the first uncertainty is statistical, the second is systematic and the third, relevant for the D$^{+}$ channels, is due to the uncertainty on $ {\mathcal{A}}^{CP}=\left({D}^{+}\to \phi {\pi}^{+}\right) $. These measurements, currently the most precise for three of the four channels considered, are consistent with the absence of CP violation. A combination of these results with previous LHCb measurements is presented.[graphic not available: see fulltext]