Measurements of Direct $CP$ Violating Asymmetries in Charmless Decays of Strange Bottom Mesons and Bottom Baryons

We report measurements of direct $CP$—violating asymmetries in charmless decays of neutral bottom hadrons to pairs of charged hadrons with the upgraded Collider Detector at the Fermilab Tevatron. Using a data sample corresponding to $1{\mathrm{fb}}^{-1}$ of integrated luminosity, we obtain the first measurements of direct $CP$ violation in bottom strange mesons, $A_{CP}(B_s^0\to K^{-}{\pi }^{+})=+0.39\pm 0.15(\mathrm{stat})\pm 0.08(\mathrm{syst})$, and bottom baryons, $A_{CP}({\Lambda }_b^0\to p{\pi }^{-})=+0.03\pm 0.17(\mathrm{stat})\pm 0.05(\mathrm{syst})$ and $A_{CP}({\Lambda }_b^0\to p{K}^{-})=+0.37\pm 0.17(\mathrm{stat})\pm 0.03(\mathrm{syst})$. In addition, we measure $CP$ violation in $B^0\to K^{+}{\pi }^{-}$ decays with $3.5\sigma$ significance, $A_{CP}(B^0\to K^{+}{\pi }^{-})=-0.086\pm 0.023(\mathrm{stat})\pm 0.009(\mathrm{syst})$, in agreement with the current world average. Measurements of branching fractions of $B_s^0\to K^{+}{K}^{-}$ and $B^0\to {\pi }^{+}{\pi }^{-}$ decays are also updated.

Figure 1

Mass distribution of the 13 502 reconstructed candidates. The charged-pion mass is assigned to both tracks. The total projection and projections of each signal and background component of the likelihood fit are overlaid on the data distribution. Signals and multibody $B$ backgrounds are shown stacked on the combinatorial background component.

Figure 2

Joint kaonness distribution for the positive (abscissa) and negative (ordinate) final state particles in $B^0\to K^{+}{\pi }^{-}$ decays as determined from the calibration data of charm decays (top left). Dipion mass as a function of $\alpha$ for simulated ${\Lambda }_b^0\to p{K}^{-}$ decays (top right). Mass of $D^0\to h^{+}{h}^{\prime -}$ candidates with pion assignment to both final state particles (bottom left). Same quantity as a function of $\alpha$ for simulated $D^0\to h^{+}{h}^{\prime -}$ decays (bottom right).