Measurements of $A_{CP}(B^0\to K^{+}{\pi }^{-})$ and $A_{CP}(B_s\to {\pi }^{+}{K}^{-})$ at LHCb

The LHCb experiment is designed to perform flavour physics measurements at the Large Hadron Collider. Using data collected during the 2010 run, we reconstruct a sample of $H_b\to h^{+}{h}^{\mathrm{\prime }-}$ decays, where $H_b$ can be either a $B^0$ meson, a $B_s^0$ meson or a ${\mathrm{\Lambda }}_b$ baryon, while $h$ and $h^{\mathrm{\prime }}$ stand for $\pi$, $K$ or $p$. We provide preliminary values of the direct $\mathcal{C}\mathcal{P}$ asymmetries of the neutral $B^0$ and $B_s^0$ mesons $A_{CP} (B^0\rightarrow K^+\pi^-) = -0.074 \pm 0.033$(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})$ \pm 0.008$(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})$$and$A_{CP}(B_s^0\rightarrow\pi^+K^-)=0.15 \pm 0.19$(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})$ \pm 0.02$(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.})$$.