Evidence for $C\!P$ violation in $B^{\pm} \to \pi^{\pm} \pi^{+} \pi^{-}$ and $B^{\pm} \to K^{+} K^{-} \pi^{\pm}$ decays

The charmless three-body decays $B^{\pm} \to \pi^{\pm} \pi^{+} \pi^{-}$ and $B^{\pm} \to K^{+} K^{-} \pi^{\pm}$ are reconstructed using 1.0 fb$^{-1}$ of data collected by LHCb in 2011. Using the decay $B^{\pm} \to J/\psi K^{\pm}$ as a control channel to determine the production and detection asymmetries, the inclusive charge asymmetries of the two modes are measured to be \begin{eqnarray} A_{C\!P}(B^{\pm} \to \pi^{\pm} \pi^{+} \pi^{-})= +0.120 \pm 0.020 ({\rm{stat}}) \pm 0.019 ({\rm{syst}})\pm 0.007 (J/\psi K^{\pm}) \, ,\nonumber \\ A_{C\!P}(B^{\pm} \to K^{+} K^{-} \pi^{\pm})= -0.153 \pm 0.046 ({\rm{stat}}) \pm 0.019 ({\rm{syst}}) \pm 0.007 (J/\psi K^{\pm})\, ,\nonumber \end{eqnarray} where the first uncertainty is statistical, the second is the experimental systematic uncertainty, and the third is the systematic uncertainty due to the $B^{\pm} \to J/\psi K^{\pm}$ reference mode. The charge asymmetries are measured at the level of 4.2 standard deviations for $B^{\pm} \to \pi^{\pm} \pi^{+} \pi^{-}$ and 3.0 standard deviations for $B^{\pm} \to K^{+} K^{-} \pi^{\pm}$. For both decay modes this is the first evidence of direct $C\!P$ violation. Larger asymmetries in localised regions of the phase space are apparent.