Search for CP violation in the decays $D^+_{(s)} to K_S^0pi^+$ and $D^+_{(s)} to K_S^0K^+$

We have searched for CP violation in the charmed meson decays $D^{+}_{(s)}to K^0_Spi^+$ and $D^{+}_{(s)}to K^0_S K^+$ using 673 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No evidence for CP violation is observed. We report the most sensitive CP asymmetry measurements to date for these decays: $A_{CP}^{D^+to K^0_Spi^+}=(-0.71pm0.19pm0.20)%$, $A_{CP}^{D^+_sto K^0_Spi^+}=(+5.45pm2.50pm0.33)%$, $A_{CP}^{D^+to K^0_S K^+}=(-0.16pm0.58pm0.25)%$, and $A_{CP}^{D^+_sto K^0_S K^+}=(+0.12pm0.36pm0.22)%$, where the first uncertainties are statistical and the second are systematic.