Study of CP-violating asymmetries in $B^0\to {\pi }^{+}{\pi }^{-},$ $K^{+}{\pi }^{-}$ decays

We present a measurement of the time-dependent CP-violating asymmetries in neutral B decays to the ${\pi }^{+}{\pi }^{-}\mathrm{CP}$ eigenstate, and an updated measurement of the charge asymmetry in $B^0\to K^{+}{\pi }^{-}$ decays. In a sample of 33 million ${\rm Y}\mathrm{}\left(4S\right)\mathrm{}\to B\overline{B}$ decays collected with the BABAR detector at the SLAC PEP-II asymmetric B factory, we find ${65}_{-11}^{+12\mathrm{}}$ ${\pi }^{+}{\pi }^{-}$ and $217\pm 18$ $K^{+}{\pi }^{-}$ candidates and measure the asymmetry parameters $S_{\pi \pi }{=0.03\mathrm{}}_{-0.56}^{+0.53\mathrm{}}\pm 0.11,$ $C_{\pi \pi }=-{0.25}_{-0.47}^{+0.45\mathrm{}}\pm 0.14,$ and ${\mathcal{A}}_{K\pi }=-0.07\pm 0.08\pm 0.02,$ where the first error is statistical and the second is systematic.