Observation of the ${\Xi }_b^0$ Baryon

The observation of the bottom, strange baryon ${\Xi }_b^0$ through the decay chain ${\Xi }_b^0\to {\Xi }_c^{+}{\pi }^{-}$, where ${\Xi }_c^{+}\to {\Xi }^{-}{\pi }^{+}{\pi }^{+}$, ${\Xi }^{-}\to \Lambda {\pi }^{-}$, and $\Lambda \to p{\pi }^{-}$, is reported by using data corresponding to an integrated luminosity of $4.2{\mathrm{fb}}^{-1}$ from $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded with the Collider Detector at Fermilab. A signal of ${25.3}_{-5.4}^{+5.6}$ candidates is observed whose probability of arising from a background fluctuation is $3.6\times {10}^{-12}$, corresponding to 6.8 Gaussian standard deviations. The ${\Xi }_b^0$ mass is measured to be $5787.8\pm 5.0(\mathrm{stat})\pm 1.3(\mathrm{syst})\mathrm{MeV}/c^2$. In addition, the ${\Xi }_b^{-}$ baryon is observed through the process ${\Xi }_b^{-}\to {\Xi }_c^0{\pi }^{-}$, where ${\Xi }_c^0\to {\Xi }^{-}{\pi }^{+}$, ${\Xi }^{-}\to \Lambda {\pi }^{-}$, and $\Lambda \to p{\pi }^{-}$.

Figure 1

(a) The ${\Xi }^{-}{\pi }^{+}$ and (b) the ${\Xi }^{-}{\pi }^{+}{\pi }^{+}$ mass distributions. The mass ranges used for the ${\Xi }_c^0$ and ${\Xi }_c^{+}$ samples are indicated by the shaded areas.

Figure 2

(a) The ${\Xi }_c^0{\pi }^{-}$ and (b) the ${\Xi }_c^{+}{\pi }^{-}$ mass distributions. A projection of the likelihood fit is overlaid as a dashed line.