Measurement of CP asymmetries in D⁺_(s) → ηπ⁺ and D⁺_(s) → η′π⁺ decays

Searches for CP violation in the decays D⁺_(s) → ηπ⁺ and D⁺_(s) → η′π⁺ are performed using pp collision data corresponding to 6 fb⁻¹ of integrated luminosity collected by the LHCb experiment. The calibration channels D⁺_(s) → ϕπ⁺ are used to remove production and detection asymmetries. The resulting CP-violating asymmetries are

A^CP = (D⁺ → ηπ⁺) = (0.34 ± 0.66 ± 0.16 ± 0.05)%,
A^CP = (D⁺_s → ηπ⁺) = (0.32 ± 0.51 ± 0.12)%,
A^CP = (D⁺ → η′π⁺) = (0.49 ± 0.18 ± 0.06 ± 0.05)%,
A^CP = (D⁺_s → η′π⁺) = (0.01 ± 0.12 ± 0.08)%,

where the first uncertainty is statistical, the second is systematic and the third, relevant for the D⁺ channels, is due to the uncertainty on A^CP = (D⁺ → ϕπ⁺) . 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.