First Flavor-Tagged Determination of Bounds on Mixing-InducedCPViolation inBs0→J/ψϕDecays

This Letter describes the first determination of bounds on the $CP$-violation parameter $2{\beta }_s$ using $B_s^0$ decays in which the flavor of the bottom meson at production is identified. The result is based on approximately 2000 $B_s^0\to J/\psi \varphi$ decays reconstructed in a $1.35{\mathrm{fb}}^{-1}$ data sample collected with the CDF II detector using $p\overline{p}$ collisions produced at the Fermilab Tevatron. We report confidence regions in the two-dimensional space of $2{\beta }_s$ and the decay-width difference $\Delta \Gamma$. Assuming the standard model predictions of $2{\beta }_s$ and $\Delta \Gamma$, the probability of a deviation as large as the level of the observed data is 15%, corresponding to 1.5 Gaussian standard deviations.