Evidence for Direct $CP$ Violation in the Measurement of the Cabbibo-Kobayashi-Maskawa Angle $\gamma$ with $B^{\mp }\to D^{(*)}{K}^{(*)\mp }$ Decays

We report the measurement of the Cabibbo-Kobayashi-Maskawa $CP$-violating angle $\gamma$ through a Dalitz plot analysis of neutral $D$-meson decays to $K_S^0{\pi }^{+}{\pi }^{-}$ and $K_S^0{K}^{+}{K}^{-}$ produced in the processes $B^{\mp }\to D{K}^{\mp }$, $B^{\mp }\to D^{*}{K}^{\mp }$ with $D^{*}\to D{\pi }^0$, $D\gamma$, and $B^{\mp }\to D{K}^{*\mp }$ with $K^{*\mp }\to K_S^0{\pi }^{\mp }$, using 468 million $B\overline{B}$ pairs collected by the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at SLAC. We measure $\gamma =(68\pm 14\pm 4\pm 3)°$ (modulo 180°), where the first error is statistical, the second is the experimental systematic uncertainty, and the third reflects the uncertainty in the description of the neutral $D$ decay amplitudes. This result is inconsistent with $\gamma =0$ (no direct $CP$ violation) with a significance of 3.5 standard deviations.

Figure 1

Contours at 39.3% (dark) and 86.5% (light) two-dimensional C.L. in the (a) ${\mathsf{z}}_{\mp }$, (b) ${\mathsf{z}}_{\mp }^{*}$, and (c) ${\mathsf{z}}_{s\mp }$ planes, corresponding to one- and two-standard deviation regions (statistical only), for $B^{-}$ (solid lines) and $B^{+}$ (dotted lines) decays.

Figure 2

$1-\mathrm{C}.\mathrm{L}.$ as a function of $\gamma$ for $B^{\mp }\to D{K}^{\mp }$, $B^{\mp }\to D^{*}{K}^{\mp }$, and $B^{\mp }\to D{K}^{*\mp }$ decays separately, and their combination, including statistical and systematic uncertainties. The dashed (upper) and dotted (lower) horizontal lines correspond to the one- and two-standard deviation intervals, respectively.