Observation of the Xi_b^0 Baryon

The observation of the bottom, strange baryon ${\mathrm{\Xi }}_b^0$ through the decay chain ${\mathrm{\Xi }}_b^0\to {\mathrm{\Xi }}_c^{+}{\pi }^{-}$, where $\Xi_c^+ \rightarrow \Xi^- , \pi^+ , \pi^+$,$\Xi^- \rightarrow \Lambda , \pi^-$,and$\Lambda \rightarrow p , \pi^-$, is reported using data corresponding to an integrated luminosity of 4.2 fb${}^{-1}$ from $p\bar{p}$ collisions at $\sqrt{s}=1.96$ 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 ${\mathrm{\Xi }}_b^0$ mass is measured to be $5787.8\pm 5.0(\text{stat})\pm 1.3(\text{syst})$ MeV/$c^2$. In addition, the ${\mathrm{\Xi }}_b^{-}$ baryon is observed through the process $\Xi^-_b \rightarrow \Xi_c^0 , \pi^-$,where$\Xi_c^0 \rightarrow \Xi^-, \pi^+$,$\Xi^- \rightarrow \Lambda , \pi^-$,and$\Lambda \rightarrow p , \pi^-$.