First Flavor-Tagged Determination of Bounds on Mixing-Induced $CP$ Violation in $B_s^0\to J/\psi \varphi$ Decays

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.

Figure 1

Invariant ${\mu }^{+}{\mu }^{-}{K}^{+}{K}^{-}$ mass distribution with the fit projection overlaid. The vertical lines indicate the mass sideband regions.

Figure 2

Feldman-Cousins confidence region in the $2{\beta }_s-\Delta \Gamma$ plane, where the standard model favored point is shown with error bars [9]. The intersection of the horizontal and vertical dotted lines indicates the reflection symmetry in the $2{\beta }_s-\Delta \Gamma$ plane.