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
ACP (D+ → ηπ+) = (0.34 ± 0.66 ± 0.16 ± 0.05)%,
ACP (D+s → ηπ+) = (0.32 ± 0.51 ± 0.12)%,
ACP (D+ → η′π+) = (0.49 ± 0.18 ± 0.06 ± 0.05)%,
ACP (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 ACP (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.